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Plain Language Summary Iceland hosts a predominantly rifting plate boundary that is offset by two ∼east-west trending, horizontally sliding (transform-faulting) segments, one in the north and the other in the south. The southern segment, known as the South Iceland Seismic Zone (SISZ), is seismically productive and is flanked by diverging volcanic arms. The SISZ has hosted several moderate to large earthquakes on north-south faults that cut across it. However, the westernmost end of the SISZ, also known as Hjalli-Ölfus, differs from the rest of the SISZ as it seems to host earthquakes in an ∼east-northeast direction, similar to its western, rifting neighbor, namely, the Reykjanes Peninsula. The activity in Hjalli-Ölfus also seems to be responsive to volcanic/magmatic activity in the Hengill volcano to its north. This suggests the existence of multiple stress fields—volcanic, tectonic, or both—acting on the Hjalli-Ölfus segment. Here, we study earthquakes in Hjalli-Ölfus from January 1991 to December 1999, including a magnitude 5.1 earthquake in November 1998, to identify possible stress changes along the segment over time. Results indicate that magmatic deformation and seismic activity near the Hengill volcano directly influence the seismic productivity of Hjalli-Ölfus, and that this seismicity is similar to that of the Reykjanes Peninsula., Hjalli-Ölfus is the westernmost segment of the east-west transform South Iceland Seismic Zone (SISZ), which is the eastward extension of the ∼ENE-trending transtensional Reykjanes Peninsula (RP). Historically, the area has shown an interactive behavior with the Hengill volcanic system to the north and the central SISZ to the east. We analyzed the state of stress and faulting mechanisms in Hjalli-Ölfus between July 1991 and December 1999, in connection with the Hengill inflation episode (Feigl et al., 2000, https://doi. org/10.1029/2000JB900209) and the 13th November 1998 Mw 5.1 Hjalli-Ölfus earthquake. We find that this region predominantly hosted oblique-normal and left-lateral strike-slip events (4–10 km-depth), with most nodal planes oriented along ∼ENE or ∼WSW directions (75° ± 15° or 255° ± 15°). We identify 5 stages of stress evolution from January 1991 to December 1999 over which Hjalli-Ölfus experiences both spatial and temporal shifts in stress-states. The Hengill inflation likely loaded both the fissure zone and western Ölfus, culminating in the Mw 5.4 (Hengill) and Mw 5.1 (Hjalli-Ölfus) earthquakes. Following these events, the maximum compressive stress (SHmax) orientation near the location of the Mw 5.1 earthquake showed a ∼5°–7° counterclockwise swing, compared to SHmax before June 1998. The average SHmax (∼40° ± 1°) and minimum principal stress (sigma3 ∼ 130° ± 1°) are comparable to geological trends in the RP. We conclude that Hjalli-Ölfus shows clockwise SHmax rotation upon loading, while a stress-drop reverses the rotation. We also posit that the region, especially the western end, behaves like the RP during interseismic periods., Icelandic Research Fund (IRF) (Rannís). Grant Number:152432-053

Publisher´s version / Útgefin grein, The 23-day long eruption of the ice-covered Katla volcano in 1918 began on October 12 and was over by November 4. Seismicity preceding and accompanying the onset had already started by 11:30 on October 12, while the eruption broke through the glacier around 3 PM. The plume rose to 14–15 km on the first day. The eruption caused widespread tephra fall, accompanied by lightning and thunder. Tephra fall from the intense first phase (October 12–14) was reported from Höfn, 200 km east of Katla, Reykjavík, 150 km to the west and Akureyri, 240 km to the north. The initial phase was followed by more sporadic activity for a week, and a second intense phase (October 22–24), with heavy tephra fall in populated areas east and south of the volcano. Skaftártunga (25–35 km east of Katla), was the worst hit farming district, with reported tephra thickness of 6.5–10 cm in total, collecting into drifts tens of cm thick. The Vík village suffered almost continuous tephra fall for 13 hours on October 24 and 25, leaving a 2 to 4 cm thick tephra layer on the ground. Tephra reached Reykjavík four times but minor tephra fallout («1 mm) occurred. Tephra also reached northern, western and eastern Iceland. In addition to producing the 0.9–1.0 km3 tephra layer, which may as freshly fallen have been 1.1–1.2 km3, the eruption was accompanied by a jökulhlaup that flooded the Mýrdalssandur plain and neighbouring areas. The jökulhlaup on October 12 had two separate phases. The first phase is considered to have flowed supraglacially down the lower parts of the Kötlujökull outlet glacier into the Leirá, Hólmsá and Skálm rivers (northern fork), and the Sandvatn and Múlakvísl rivers (southern fork). It was much more widespread than the second phase which emerged from below the glacier snout and was confined to the western part of Mýrdalssandur. That phase carried huge icebergs and massive sediment load onto the sandur plain.

Open Access funding enabled and organized by Projekt DEAL., Analyzing video data from an uncrewed aerial vehicle (UAV) of two short-lived dome building events at Anak Krakatau volcano (Indonesia), we determine vertical and horizontal movements of the dome surface prior to explosions, as well as initial eruption velocities and mass eruption rates via automated feature tracking and other photogrammetric methods. Initial eruption velocities and mass eruption rates are estimated as a proxy for eruptive strength. Eruptive strength is found to correlate with deformation magnitude, i.e., larger pre-explosion surface displacements are followed by both higher initial eruption velocities and mass fluxes. In accord with other studies, our observations can be explained by an overpressure underneath the dome’s surface. We assume that the dome seals the underlying vent efficiently, meaning that pre-explosion pressure build-up controls both deformation magnitude and eruptive strength. We support this assumption by a simple numerical model indicating that pre-explosion pressure increases between 8 and 16 MPa. The model further reveals that the two events vary significantly with respect to the importance of lateral visco-elastic flow for pressurization and deformation. The video sequences also show considerable variations in the gas release and associated deformation characteristics. Both constant and accelerating deformation is observed. Our case study demonstrates that photogrammetric methods are suitable to provide quantitative constraints on both effusive and explosive activity. Future work can build on our or similar approaches to develop automated monitoring strategies that would enable the observation and analysis of volcanic activity in near real time during a volcanic crisis., We would like to thank M. Rietze, who kindly provided us with the video sequences used in this study. He also supplied all the additional information on the video acquisition without which the processing of the films would not have been possible. TD is supported by the Icelandic Research Fund grant Nr. 206527-051. Additionally, we would like to thank Michael R. James for acting as associate editor and for providing us with helpful comments on the manuscript. Likewise, we are grateful to Richard Herd and an anonymous reviewer for their constructive comments and suggestions., Pre-print (óritrýnt handrit)

Publisher's version (útgefin grein), Oldoinyo Lengai, located in the Gregory Rift in Tanzania, is a world-famous volcano owing to its uniqueness in producing natrocarbonatite melts and because of its extremely high CO2 flux. The volcano is constructed of highly peralkaline [PI = molar (Na2O + K2O)/Al2O3 > 2–3] nephelinite and phonolites, both of which likely coexisted with carbonate melt and a CO2-rich fluid before eruption. Results of a detailed melt inclusion study of the Oldoinyo Lengai nephelinite provide insights into the important role of degassing of CO2-rich vapor in the formation of natrocarbonatite and highly peralkaline nephelinites. Nepheline phenocrysts trapped primary melt inclusions at 750–800 °C, representing an evolved state of the magmas beneath Oldoinyo Lengai. Raman spectroscopy, heating-quenching experiments, low current EDS and EPMA analyses of quenched melt inclusions suggest that at this temperature, a dominantly natritess-normative, F-rich (7–14 wt%) carbonate melt and an extremely peralkaline (PI = 3.2–7.9), iron-rich nephelinite melt coexisted following degassing of a CO2 + H2O-vapor. We furthermore hypothesize that the degassing led to re-equilibration between the melt and liquid phases that remained and involved 1/ mixing between the residual (after degassing) alkali carbonate liquid and an F-rich carbonate melt and 2/ enrichment of the coexisting nephelinite melt in alkalis. We suggest that in the geological past similar processes were responsible for generating highly peralkaline silicate melts in continental rift tectonic settings worldwide., This study was financially supported by project NRDIO ( National Research, Development, and Innovation Office of Hungary ) K-119535 (to M. Berkesi and T. Guzmics) and by the Betta Üzletlánc Ltd. to Guzmics. In addition, M. Berkesi acknowledges to the ELTE Institutional Excellence Program (1783-3/2018/FEKUTSRAT) supported by the Hungarian Ministry of Human Capacities . We thank Toshiaki Tsunogae for his editorial handling, and Alan Cooper and an anonymous reviewer for their constructive comments that helped to improve the manuscript.

Publisher's version (útgefin grein), Since the mid-1970s radio-echo soundings have been conducted on Iceland's temperate glaciers. Since then, low-frequency radar technology has furthered the study of most of the island's ice caps. Their masses and volumes have been quantified and detailed subglacial topographic maps produced which demarcate glacial drainage basins and identify subglacial lakes and volcanoes. Even internal tephra layers have been charted. The resulting data have been used to force and validate models of past and future glacier evolution. Many practical applications in glacier hydrology have come into being, including hydropower management, road and bridge planning and the prediction of catastrophic flood paths from subglacial eruption sites. Finally, emerging landscapes can now be foreseen in places where glaciers may soon disappear. These achievements would not have been possible without the advances in RES technology., The work was supported by The National Power Company of Iceland, The Road and Coastal Administration of Iceland, The Parliament Financial Committee and the Research Fund of Eggert V. Briem. Special thanks to our colleague Eyjólfur Magnússon who processed the digital RES and for fruitful discussion on the paper content. We are grateful to Philip Vogler for improving the English text of the manuscript.

Publisher's version (útgefin grein), In this paper, we give an overview of changes in area, length, surface elevation and mass balance of glaciers in mainland Norway since the 1960s. Frontal advances have been recorded in all regions except the northernmost glaciers in Troms and Finnmark (Storsteinsfjellbreen, Lyngen and Langfjordjokelen). More than half of the observed glaciers, 27 of 49, had marked advances in the 1990s. The glaciological mass-balance values for the period 1962-2018, where 43 glaciers have been measured, show great inter-annual variability. The results reveal accelerated deficit since 2000, the most negative decade being 2001-2010. Some years with a positive mass balance (or less negative) after 2010s can be attributed to variations in large-scale atmospheric circulation. A surface elevation change and geodetic mass balance were calculated for a sample of 131 glaciers covering 817 km in the '1960s' and 734 km in the '2010s', giving an area reduction of 84 km, or 10%. The sample covers many of the largest glaciers in Norway, and they had an overall change in surface elevation of -15.5 m for the ~50 year period. Converted to a geodetic mass balance this gives a mean mass balance of -0.27 ± 0.05 m w.e. a-1, The dataset of Norwegian glaciers would not be possible without all the observers who helped collecting them. We thank colleagues at NVE, our front position observers and personnel from hydropower companies. We thank Rune V. Engeset, NVE, for providing input to the manuscript. We thank John Brittain, NVE, for English corrections. We thank two anonymous reviewers for input to the manuscript, and editor C. Schneider for handling the manuscript. Statkraft is thanked for partly funding the laser scannings. We thank Trygve Snøtun and Goeffrey D. Corner for providing information on length change advances and records. Torgeir Ferdinand Klingenberg helped digitising some of the glacier outlines. We thank Etienne Berthier for providing Pléiades (@CNES & Airbus D&S) imagery of Svartisen 2016 and processing the data resulting in orthophotos and DTMs. We thank the Norwegian Mapping Authority (Kartverket) for proving orthophotos through norgeibilder.no, a valuable source for glacier status. The work is a contribution to the CryoClim, Svali and Copernicus Glacier Service projects, and internal NVE project ‘Massebalanse’.

Real-time monitoring of volcanic ash plumes with the aim to estimate the mass eruption rate is crucial for predicting atmospheric ash concentration. Mass eruption rates are usually assessed by 0D and 1D plume models, which are fast and require only a few observational input parameters, often only the plume height. A model’s output, however, depends also on the plume height data handling strategy (sampling rate, gap reconstruction methods and statistical treatment), especially in long-term eruptions with incomplete plume height records. Representing such an eruption, we used Eyjafjallajökull 2010 to test the sensitivity of six simple and two explicitly wind-affected plume models against 22 data handling strategies. Based on photogrammetric measurements, the wind deflection of the plume was determined and used to re-calibrate radar height data. The resulting data was then subjected to different data handling strategies, before being used as input for the plume models. The model results were compared to the erupted mass measured on the ground, allowing us to assess the prediction accuracy of each combination of data handling strategy and model. Combinations that provide highest prediction accuracies vary, depending on data coverage, eruptive strength, and fragmentation style. However, for this type of moderate to weak eruption, the most important factor was found to be the prevailing windspeed. When windspeeds exceed 20 m/s, most combinations of strategies and models provide predictions that underestimate the erupted mass by more than 40%. Under such conditions, the optimal choice of data handling strategy and plume model is of particularly relevance., The geo-referencing and photo analysis was conducted under the EU Framework 7 FutureVolc project (2012–2016). This work contributes to project MAXI-Plume, supported by the Icelandic Research Fund (Rannís), grant Nr. 206527-051. TD was supported by the IRF (Rannís) Postdoctoral project grant 206527–051., Pre-print (óritrýnt handrit)

Pre-print version (óritrýnt handrit), Juvenile pyroclasts, especially in the ash size range, provide important information on primary fragmentation processes, i.e., initial explosive magma fragmentation, and on the state of the magma both prior to and at the point of fragmentation and quenching. There exists an extensive body of literature focusing on the quantification of juvenile particle morphology (shape), internal textures, and surface features spanning several decades; however, a standardized method has yet to emerge for comparative studies. No community-wide consensus currently exists (i) regarding the most representative size fraction(s) to be examined, (ii) on sample preparation procedures (such as whether to use whole-particle silhouettes or 2D cross-sections), (iii) on imaging techniques and image acquisition parameters, or (iv) on the optimal morphometric parameters to measure. Lack of a standardized method precludes robust comparison between different studies and laboratories. We propose here a preliminary “best practices” and workflow for characterization of juvenile pyroclasts, for comparative studies of primary fragmentation. If the community follows such a standardized method, it will become possible to accumulate a large volume of consistent data on juvenile pyroclasts from a range of eruption styles, fragmentation mechanisms, and magma compositions. This will ultimately allow deeper insights into the full panoply of magma-to-pyroclast processes that drive particle-producing volcanic eruptions. One or more “fragmentation diagrams” may eventually be developed to allow different types of magmatic and phreatomagmatic explosive eruptions to be distinguished based on their products.

Pre-print (óritrýnt handrit), The morphological and textural features of juvenile pyroclasts record crucial details on magma conditions at the time of fragmentation. Their study is therefore essential to better understand the dynamics of explosive eruptions. Unfortunately, the absence of a standardized protocol of investigation hinders data reproducibility and comparison among different laboratories. Here we focus on morphometric parameters, 2D crystallinity and 2D vesicularity resulting from cross-section analysis of juvenile particles using backscattered electron imaging, and address the following questions: (i) how to prepare polished epoxy grain mounts, (ii) which pixel density to be used, (iii) how to facilitate image preparation and image analysis, (iv) which sample size is necessary to obtain statistically robust results, and (v) what is the optimum size fraction for analysis. We test juvenile particles in grain size bins ranging from 2–1 mm (− 1 to 0ɸ) to 88–63 µm (+ 3.5 to + 4ɸ), using samples from the 1977 Ukinrek eruption. We find that the required resolution ranges from 75 000 to 10 000 pixels per particle, depending on the size fraction, higher than previously postulated. In the same size ranges, less than 50 grains per size fraction and sample are needed to get robust averages. Based on theoretical, empirical, and practical considerations, we propose 0.71–0.5 mm (+ 0.5 to + 1ɸ) as the optimum size fraction to be analyzed as particle cross-sections in standardized comparative studies of magma fragmentation. We provide a detailed guide for preparing polished epoxy grain mounts and introduce a software package (PASTA) for semi-automated image preparation, image processing, and measurement of morphological and textural parameters., This study was funded by a Discovery Grant to PSR from the Natural Sciences and Engineering Research Council of Canada (NSERC) (RGPIN-2015–06782). TD is supported by the Icelandic Research Fund (Rannís), grant Nr. 206527–051.

Due to poor preservation and lack of proximal tephra thickness data, no comprehensive isopach map has existed for the tephra layer from the major eruption of the Katla volcano in 1918. We present such a map obtained by combining existing data on the thickness of the 1918 tephra in soil profiles with newly acquired data from the 590 km2 Mýrdalsjökull ice cap which covers the Katla caldera and its outer slopes. A tephra thickness of 20–30 m on the ice surface proximal to the vents is inferred from photos taken in 1919. The greatest thicknesses presently observed, 30–35 cm, occur where the layer outcrops in the lowermost parts of the ablation areas of the Kötlujökull and Sólheimajökull outlet glaciers. A fallout location within the Katla caldera is inferred for the presently exposed tephra in both outlet glaciers, as estimates of balance velocities imply lateral transport since 1918 of ∼15 km for Kötlujökull, ∼11 km for Sólheimajökull and about 2 km for the broad northern lobe of Sléttjökull. Calculations of thinning of the tephra layer during this lateral transport indicate that the presently exposed tephra layers in Kötlujökull and Sólheimajökull were respectively over 2 m and about 1.2 m thick where they fell while insignificant thinning is inferred for the broad northern lobe of Sléttjökull. The K1918 layer has an estimated volume of 0.95±0.25 km3 (corresponding to 1.15±0.30×1012 kg) whereof about 50% fell on Mýrdalsjökull. About 90% of the tephra fell on land and 10% in the sea to the south and southeast of the volcano. The volume estimate obtained contains only a part of the total volume erupted as it excludes water-transported pyroclasts and any material that may have been left on the glacier bed at the vents. While three main dispersal axes can be defined (N, NE and SE), the distribution map is complex in shape reflecting tephra dispersal over a period of variable wind directions and eruption intensity. In terms of airborne tephra, Katla 1918 is the largest explosive eruption in Iceland since the silicic eruption of Askja in 1875., MTG, ÞH: University of Iceland Research Fund, Chief of Police in South Iceland, The Icelandic Road Authority. MHJ: EU Marie Sklodowska-Curie fellowship JG: Landsvirkjun, Fræðslusjóður Suðurlands TJ: GOSVÁ program on volcanic hazard assessment in Iceland

A 3 day exercise simulating unrest and a large explosive eruption at Katla volcano, Iceland, was conducted in January 2016. A large volume of simulated data based on a complex, but realistic eruption scenario was compiled in advance and then transmitted to exercise participants in near-real time over the course of the exercise. The scenario was designed to test the expertise and procedures of the local institutions in charge of warning and responding to volcanic hazards, namely the volcano observatory, national civil protection, and the local university-science sector, as well as their interactions with the European science community and the London Volcanic Ash Advisory Centre. This exercise was the first of this magnitude and scope in Iceland and has revealed many successful developments introduced since the 2010 Eyjafjallajökull and 2011 Grímsvötn eruptions. Following the exercise, 90% of participants said that they felt better prepared for a future eruption. As with any exercise, it also identified areas where further development is required and improvements can be made to procedures. Seven key recommendations are made to further develop capability and enhance the collaboration between the volcano observatory, volcano research institutions and civil protection authorities. These recommendations cover topics including notification of responders, authoritative messaging, data sharing and media interaction, and are more broadly applicable to volcanic institutions elsewhere. Lessons and suggestions for how to run a large-scale volcanic exercise are given and could be adopted by those planning to rehearse their own response procedures., This work was funded by the European Community’s FP7 Programme grant 308377 (Project FUTUREVOLC).

Publisher's version, Supercritical fluids exist in the roots of many active high-temperature geothermal systems. Utilization of such supercritical resources may multiply energy production from geothermal systems; yet, their occurrence, formation mechanism, and chemical properties are poorly constrained. Flow-through experiments at 260°C and 400-420°C were performed to study the chemical and mineralogical changes associated with supercritical fluid formation near shallow magmatic intrusions by conductive heating and boiling of conventional subcritical geothermal fluids. Supercritical fluids formed by isobaric heating of liquid geothermal water had similar volatile element concentrations (B, C, and S) as the subcritical water. In contrast, mineral-forming element concentrations (Si, Na, K, Ca, Mg, and Cl) in the supercritical fluid were much lower. The results are consistent with the observed mineral deposition of quartz, aluminum silicates, and minor amount of salts during boiling. Similar concentration patterns have been predicted from geochemical modeling and were observed at Krafla, Iceland, for the IDDP-1 supercritical fluid discharge. The experimental results confirm previous findings that supercritical fluids may originate from conductive heating of subcritical geothermal reservoir fluids characterized by similar or lower elemental concentrations with minor input of volcanic gas., We would like to thank Ríkey Kjartansdóttir, Andri Ísak Thórhallsson, and Helgi Arnar Alfreðsson for their valuable help. This work was funded by the Swiss National Science Foundation (CRSII2_1418431/1, Sinergia COTHERM), Georg (11-04-003), and The Energy Research Fund of Landsvirkjun in 2018 and 2019.

Publisher's version (útgefin grein)., The extensive lava piles of Iceland contain a unique record of geomagnetic field variations spanning the past ~ 16 Ma. Since the 1950s, palaeomagnetic data have been obtained from over 9400 Icelandic lavas. We have compiled all palaeomagnetic data currently available and developed a publicly accessible database (http://www.icepmag.org). The data within the database are primarily palaeodirections, with a relatively smaller number of palaeointensity data (8936 entries contain direction only, 218 intensity only, and 337 both direction and intensity). In addition, the database contains a wide range of metadata, including geochronological information, site details, and laboratory methods. The search interface of the database allows users to search for data using a range of customisable filters (e.g. by publication, geological age, location, laboratory method, palaeomagnetic statistics) and to quickly visualise and download the matching search results. The data within the database have significant potential for understanding long-term palaeomagnetic field variations at high latitude, the behaviour of excursions and reversals, and geological mapping on Iceland.[Figure not available: see fulltext.]., This project was completed as part of a Master’s programme at the University of Iceland Faculty of Earth Sciences and no funding was received.

Publisher's version (útgefin grein), The 2017 Surtsey Underwater volcanic System for Thermophiles, Alteration processes and INnovative concretes (SUSTAIN) drilling project at Surtsey volcano, sponsored in part by the International Continental Scientific Drilling Program (ICDP), provides precise observations of the hydrothermal, geochemical, geomagnetic, and microbiological changes that have occurred in basaltic tephra and minor intrusions since explosive and effusive eruptions produced the oceanic island in 1963-1967. Two vertically cored boreholes, to 152 and 192m below the surface, were drilled using filtered, UV-sterilized seawater circulating fluid to minimize microbial contamination. These cores parallel a 181m core drilled in 1979. Introductory investigations indicate changes in material properties and whole-rock compositions over the past 38 years. A Surtsey subsurface observatory installed to 181m in one vertical borehole holds incubation experiments that monitor in situ mineralogical and microbial alteration processes at 25-124 °C. A third cored borehole, inclined 55° in a 264° azimuthal direction to 354m measured depth, provides further insights into eruption processes, including the presence of a diatreme that extends at least 100m into the seafloor beneath the Surtur crater. The SUSTAIN project provides the first time-lapse drilling record into a very young oceanic basaltic volcano over a range of temperatures, 25-141 °C from 1979 to 2017, and subaerial and submarine hydrothermal fluid compositions. Rigorous procedures undertaken during the drilling operation protected the sensitive environment of the Surtsey Natural Preserve., Funding for this project was provided by the International Continental Scientific Drilling Program (ICDP) through a grant to the SUSTAIN project (led by Marie D. Jackson); a grant of excellence from the Icelandic Research Fund, ICFRANNÍS (the IceSUSTAIN consortium led by Magnús T. Gudmundsson); the Bergen Research Foundation and K.G. Jebsen Centre for Deep Sea Research at the University of Bergen, Norway (led by Steffen Leth Jørgensen); the German Research Foundation (DFG) (led by Wolfgang Bach and Bernd Zimanowski); and DiSTAR, Federico II, University of Naples, Federico II, Italy (led by Piergiulio Cappelletti). The University of Utah, USA (Marie D. Jackson), and the two Icelandic power companies Reykjavík Energy and Landsvirkjun contributed additional funds. In kind support by several Icelandic institutions and companies contributed greatly to the success of the project, as did the dedicated work of several volunteers. The logistical support provided by the Icelandic Coast Guard was instrumental in carrying out the drilling operation. Norðurflug Helicopters and the Vestmannaeyjar Rescue Group provided critical logistical support. Jeremy Fisher and Rowan McGuire contributed to this article. The DOSECC drilling team, Steve Cole, Justin Blouin, A. J. Vecchiarelli, Matthew Lyon, and Michael Vinson, did excellent work. Hjalti Franzson provided guidance, and Þorsteinn Jónsson, Bjarni Kristinsson, Gísli Sighvatsson, and Sveinbjörn Steinþórsson contributed to the logistical operation on Surtsey. Unpublished borehole temperature measurements were made during the annual Surtsey Research Society expedition in July 2018.

Publisher's version (útgefin grein), Ostracods in Icelandic freshwaters have seldom been researched, with the most comprehensive record from the 1930s. There is a need to update our knowledge of the distribution of ostracods in Iceland as they are an important link in these ecosystems as well as good candidates for biomonitoring. We analysed 25,005 ostracods from 44 lakes, 14 springs, and 10 cave pools. A total of 16 taxa were found, of which seven are new to Iceland. Candona candida (Müller, 1776) is the most widespread species, whereas Cytherissa lacustris (Sars, 1863) and Cypria ophtalmica (Jurine, 1820) are the most abundant, showing great numbers in lakes. Potamocypris fulva (Brady, 1868) is the dominant species in springs. While the fauna of lakes and springs are relatively distinct from each other, cave pools host species that are common in both lakes and springs. Icelandic non-marine ostracods include mostly generalist species, as well as species adapted to cold climates and resemble those of other north European countries while sharing very few species with the North American Arctic. Iceland is experiencing impacts from climate change and a booming tourism. It is possible to use selected freshwater ostracods as biomonitoring tools by constructing a detailed database of these species., Many thanks to the University of Iceland Research Fund and Watanabe Trust Fund for providing financial assistance that made this project possible. We thank Doriane Combot for kindly providing the ostracod samples from cave pools, and all the staff at the Natural History Museum of Kópavogur that provided assistance with the sampling over the years. We are also thankful to the reviewers for their valuable insight and comments that helped this research reach a higher quality. The authors declare no competing financial interests.

Publisher's version (útgefin grein), Andisols are carbon-rich soils that persist in volcanic regions with cool climates. They are the main soil type in Iceland, where there are also large areas of premature or degraded mineral soils with the possible potential to become andisols. This study examines soils from vegetated and unvegetated sites to look at the earliest indicators of andisol formation and soil organic carbon accumulation. Soils from 12 sites in the southern Icelandic highlands, which are characterised by harsh climate, shallow soils and limited vegetation cover, were sampled at four depths (0–5 cm, 5–10 cm, 10–20 cm and 20–30 cm). Three sites were sparsely vegetated gravels (M1–M3) and nine were fully vegetated, including 8 grassland sites (G1–G8) with mosses and dwarf shrubs, and a sandy fluvial wetland (S) with grasses, mosses and dwarf shrubs. Soils with vegetative cover were characterised as weak or structureless ranging from loamy sand to silty clay loam, while soils at the sparsely vegetated sites were structureless and sandy. The soil depth is greater in the vegetated sites, indicating greater soil development. On average, the bulk density of soils (0.75–1.16 g cm−3) was lower at vegetated sites than sparsely vegetated sites (0.90–1.17 g cm−3). The average carbon (%C), nitrogen (%N) and the overall soil organic matter (%SOM) of vegetated sites were higher (1.60%C, 0.10%N, 4.9%SOM) than for sparsely vegetated sites (0.27%C, 0.02%N, 1.81%SOM) with lower pH at the vegetated sites (pH < 7.2) than the sparsely vegetated (pH > 7.2), indicating the difference in soil development. Silandic allophanic material is present throughout the study area: all soils had >10% amounts of amorphous clay minerals (allophane, ferrihydrite or aluminium-humus complexes) and high aluminium and iron percentages. Strong associations between pyrophosphate-extractable Fe and Al and the soil C, indicative of Al and Fe complexed with humus or allophane and ferrihydrite clays of vegetated sites were observed. The %C, %SOM, Fe/Al associations, soil structure and soil depth all suggest that there is gradient of increasing soil genesis from sparsely vegetated to vegetated sites. Although the soils at the vegetated sites may be considered to be andisols, they are still immature, while the less developed soils at the sparsely vegetated sites are vitrisols (, The research was financed by Landsvirkjun and we specially wish to thank Hákon Aðalsteinsson, of Lansvirkjun, for his interest and support of this project. We would also like to thank María Svavarsdóttir, Höskuldur Þorbjarnarson, Olga Kolbrún Vilmundardóttir, Eydís S. Eiríksdóttir, and Friðþór Sófus Sigurmundsson of the University of Iceland, Brita Berglund of the Agricultural University of Iceland and Joe Jephson.

Post-print, Glaciovolcanic deposits at Tongariro and Ruapehu volcanoes, New Zealand, represent diverse styles of interaction between wet-based glaciers and andesitic lava. There are iceconfined lavas, and also hydroclastic breccia and subaqueous pyroclastic deposits that formed during effusive and explosive eruptions into meltwater beneath the glacier; they are rare among globally reported products of andesitic glaciovolcanism. The apparent lack of hydrovolcanically fragmented andesite at ice-capped volcanoes has been attributed to a lack of meltwater at the interaction sites because either the thermal characteristics of andesite limit meltwater production or meltwater drains out through leaky glaciers and down steep volcano slopes. We used published field evidence and novel, dynamic andesite-ice experiments to show that, in some cases, meltwater accumulates under glaciers on andesitic volcanoes and that meltwater production rates increase as andesite pushes against an ice wall. We concur with models for eruptions beneath ice sheets showing that the glacial conditions and pre-eruption edifice morphology are more important controls on the style of glaciovolcanism and its products than magma composition and the thermal properties of magmas. Glaciovolcanic products can be useful proxies for paleoenvironment, and the range of andesitic products and the hydrological environments in which andesite erupts are greater than hitherto appreciated., R.P. Cole received funding from the Geological Soci-ety of New Zealand Wellman Research Award and the University of Otago Polar Environments Research Theme. The New Zealand Department of Conserva-tion provided logistical assistance in the field. Brent Pooley and Luke Easterbrook assisted with making the experimental apparatus. Matteo Demurtas helped Cole in using MatLab. Kelly Russell, John Smellie, and Alison Graettinger provided constructive reviews.

In 2012, the eruption of deep-sea volcano Havre produced an abundance of fine ash at a depth of ~ 1000 m below sea level. In this study the 2D shapes of Havre ash grains retrieved from the seafloor were compared quantitatively with those of particles generated in a suite of different fragmentation experiments, which used remelted rhyolitic rock and pumice from the eruption site. A new statistical data analysis technique, denoted as Dendrogrammatic Analysis of Particle Morphology (DAPM) is introduced. It is designed to compare large numbers of morphometric data sets containing shape information for a set of ash particles to group them by morphological similarities and to visualize these clusters in a dendrogram. Further steps involve t tests and equivalence tests and reveal morphometric differences as well as matching features. The DAPM suggests that the majority of Havre ash was thermohydraulically produced by induced fuel coolant-interaction. A subset of ash particles features an elongated tube morphology. Their morphometry matches that of particles that were experimentally produced by a combination of shearing and quenching, and we infer that the natural particles were formed by synextrusive ash-venting., This study was supported by MARSDEN grant U001616; Havre samples were obtained with NSF funding EAR1447559. T.D. is supported by the Icelandic Research Fund (Rannís) Grant Nr. 206527-051. R.J.C. was funded by Australian Research Council grants DP110102196 and DE150101190, and by US National Science Foundation grant OCE1357443.

Publisher's version (útgefin grein), We synthesize the current understanding of glacier activity on Svalbard from the end of the Late Pleistocene (12,000 yrs. before present) to the end of the Little Ice Age (c. 1920 AD). Our glacier history is derived from the SVALHOLA database, the first compilation of Holocene geochronology for Svalbard and the surrounding waters, including over 1,800 radiocarbon, terrestrial cosmogenic nuclide and optically stimulated luminescence ages. Data have been categorized by geological setting, uniformly (re-)calibrated, quality assessed and ultimately used to constrain glacier fluctuations (deglaciation, ice free conditions, glacier re-advances and ice marginal positions). We advance existing knowledge by mapping the extent and distribution of ice-cover during the Holocene glacial maximum and the glacial minimum, as well as present retreat rates (and percentages) within Early Holocene fjord-systems. Throughout the Holocene, Svalbard glaciers have responded to a varying combination of climatic, environmental and dynamic driving factors which influence both the extent and behavior of ice margins. We discuss the complexities of glacier systems and their dynamics in response to changes in climate. This review provides a holistic state of the art of Holocene glaciers on Svalbard, suitable for orienting future works which address gaps in our current knowledge., Fianancial support has been provided by the Svalbard Environmental Protection Fund (16/35; to WRF), the Carlsberg Foundation (CF14-0756 to AS), The University Center in Svalbard (UNIS) (research grant to ÓI), and Arctic Research and Studies funded by the Ministries for Foreign Affairs of Norway and Iceland (2017-ARS-79772 to AS & WRF). We are grateful for extensive support from the UNIS Library (Berit Jakobsen and Catherine Fjeldstad). Constructive comments from and discussions with Skafti Brynjólfsson, Kelly Hogan, Anna L.C. Hughes, Sofia Kjellman, Nicolaj K. Larsen and Anne Sofie Søndergaard have improved this manuscript. We are also thankful for anonymous reviews as well as constructive comments from Managing Editor, Professor Negri.

Publisher's version (útgefin grein), Volcanic ash in the atmosphere is a hazard to aviation. To predict which areas of airspace are most likely to be affected by the presence of ash, Volcanic Ash Advisory Centers (VAACs) use observations and atmospheric dispersion models. These models are initialized with, among other parameters, a mass eruption rate (MER), which quantifies the emission rate into the atmosphere at the source. This influences the predicted spatial–temporal evolution and concentration of the ash cloud. Different models are available to estimate MER from the volcanic plume height and some models also include the weather conditions (e.g., wind speed). The REFIR software tool uses time-series of plume height estimated from observations and weather data to provide estimates of MER through time. Here we present an updated version of REFIR that can now be used also to calculate MER for past eruptions and produce output parameters in a format suitable for use with the NAME dispersion model (UK Met Office—London VAAC). We also investigate how uncertainty in input parameters is propagated through to dispersion model output. Our results show that a +/−1 km uncertainty on a 6 km high plume can result in the affected area ranging by a factor of three between the minimum and maximum estimates. Additionally, we show that using wind-affected plume models results in affected areas that are five times larger than using no-wind-affected models. This demonstrates the sensitivity of MER to the type of plume model chosen (no-wind- vs. wind-affected)., We thank Larry Mastin, Arnau Folch, and an anonymous reviewer for their comments and suggestions that contributed to the improvement of the manuscript, and Lynn Russell for the editorial handling. We also thank Dr. Susan Loughlin (British Geological Survey), Dr. Susan Leadbetter (UK Met Office) and Dr. Claire Witham (UK Met Office) for their valuable suggestions. Fabio Dioguardi and John A. Stevenson have been supported from UK National Capability funding (BGS Innovation Flexible Fund). Fabio Dioguardi has also been supported by the European Union's Horizon 2020 project EUROVOLC (grant agreement no 731070). Tobias D?rig's work is supported by the Icelandic Research Fund (Rann?s) grant no. 206527-051. This work is published with permission of the Executive Director of British Geological Survey (UKRI)

Publisher's version (útgefin grein), The Ölfus seismic belt lies at the western end of the ~E‐W sinistral transform shear zone in South Iceland, called the South Iceland Seismic Zone (SISZ), where most seismicity and surface faulting show ~N‐S dextral slip. Unlike the rest of SISZ, seismicity in west Ölfus is predominantly along the ~ENE‐WSW direction. Throughout recorded history, Ölfus has shown an interactive behavior with the Hengill volcanic system that lies northwest of the zone. For instance, the 13 November 1998 Mw 5.1 earthquake in the Hjalli area (west Ölfus) and its ~ENE trending aftershock sequence were likely triggered by the 4 June 1998 Mw 5.4 Hengill earthquake sequence. These events point to an interplay between conjugate ~N‐S and ~ENE‐WSW faults in the region. Relative relocations of earthquakes in Hjalli‐Ölfus from July 1991 to December 1999 (Icelandic Meteorological Office, 2017) are chiefly limited to 4‐ to 8‐km depth along the ~ENE direction with a few distributed on smaller ~N‐S faults. The foreshocks of the November 1998 earthquake occurred on a ~N‐S fault until a day prior to the mainshock when they shifted to the ~ENE direction. The subsequent aftershocks are also mainly restricted to the ~ENE direction. We find that the Mw 5.1 (Global Centroid Moment Tensor moment = 5.43 × 10E16 N‐m) Hjalli‐Ölfus earthquake ruptured a near‐vertical ~ENE fault area of 24–40 km2 with left‐lateral average slip of 5–8 cm. Multiple relocations of the mainshock using various constraints indicate that the event likely occurred close to the junction of the conjugate ~ENE‐WSW and ~N‐S faults., This study was part of the project titled “4D seismic of the South Iceland Seismic Zone: Strong earthquake forecasting” (152432‐053) funded by the Icelandic Research Fund (IRF) (Rannís). The authors thank Felix Waldhauser for sharing a more recent version of the hypoDD routine, which was then modified for the purposes of this study, and for advice on fine‐tuning the analyses. The authors thank Haukur Jóhannesson, Kristján Sæmundsson, Árni Hjartarson, Maryam Khodayar, Leó Kristjánsson, and Ágúst Guðmundsson for insightful discussions. The authors also thank Páll Einarsson and Bryndís Brandsdóttir for scientific discussion and for sharing seismic data from 1974 to 1987. The project facilitated the procurement of seismic data recorded by the SIL seismic network from the Icelandic Meteorological Office (IMO), and the raw version of this data can only be obtained directly from the agency.

Publisher's version (útgefin grein), Several cryptotephra layers that originate from Icelandic volcanic eruptions with a volcanic explosivity index (VEI) of ≤ 4 and tephra volumes of < 1 km3 have previously been identified in Northern Europe, albeit within a restricted geographical area. One of these is the Hekla 1947 tephra that formed a visible fall-out in southern Finland. We searched for the Hekla 1947 tephra from peat archives within the previously inferred fall-out zone but found no evidence of its presence. Instead, we report the first identification of Hekla 1845 and Hekla 1510 cryptotephra layers outside of Iceland, the Faroe Islands, Ireland and the UK. Additionally, Hekla 1158 tephra was found in Finland for the first time. Our results confirm that Icelandic eruptions of moderate size can form cryptotephra deposits that are extensive enough to be used in inter-regional correlations of environmental archives and carry a great potential for refining regional tephrochronological frameworks. Our results also reveal that Icelandic tephra has been dispersed into Finnish airspace at least seven times during the past millennium and in addition to a direct eastward route the ash clouds can travel either via a northerly or a southerly transport pathway., We thank Sami Jokinen for assistance with field work in Finland and Dr Maria Janebo for field assistance in Iceland. Professor Siwan Davies and Dr Gwydion Jones at Swansea University are thanked for their help with micromanipulator work. We are grateful to Dr Chris Hayward for support with EPMA at the University of Edinburgh. Financial support for field work and EPMA was received from the Finnish Cultural Foundation, Varsinais-Suomi Regional Fund and Suomen Tiedeseura. Maarit Kalliokoski acknowledges funding from the Nordic Volcanological Centre at the University of Iceland and the Doctoral Programme in Biology, Geography and Geology at the University of Turku.

Publisher's version (útgefin grein), The Negev Desert in southern Israel hosts a number of late Cenozoic lacustrine and palustrine sedimentary sequences that attest for past wetter conditions in what today constitutes one of the driest deserts on Earth. These sequences are of special importance because the Negev Desert forms part of the Levantine Corridor, which was probably the only continental bridge that enabled initial out-of-Africa expansion of our genus Homo. Yet, the paleoclimatic significance of these sequences still remains unknown, mainly due to their uncertain (late Pliocene to early Pleistocene) age. Here we present a combined sedimentologic, paleontologic and magnetostratigraphic study of one of these sedimentary sequences, the so-called Kuntila Lake sediments, which was carried out at the 30 m-thick Kuntila Gate section in the Nahal Paran basin, southern Israel. Sedimentological evidence and ostracod faunas indicate that these sediments accumulated in a long-lasting lacustrine basin that underwent periodic lake-level variations. Magnetostratigraphic measurements enable the recognition of a normal (N1) and a reverse (R1) polarity zone in the lower and upper halves, respectively, of the Kuntila Gate section. Correlation of N1 to the Olduvai Subchron (1.778–1.945 Ma) appears as the most likely option in view of previously published 10Be ages derived for the uppermost part of the Kuntila Member in nearby sections. The large errors associated with these ages, however, suggest that correlation of N1 to Subchron C2An.1n (2.582–3.032 Ma) is also possible. Although our results do not resolve the age of the Arava Formation, they unequivocally relate the Kuntila Lake sediments with a long period of enhanced climatic variability because the tops of both subchrons are associated with 400 kyr eccentricity maxima. The inferred wetter conditions in the Negev Desert concurred, regardless of the age correlation, with periods of lake expansion in East Africa and clusters of short-lived expansions of the savannah throughout much of the Sahara. This would have facilitated the biogeographic connection between Africa and Eurasia, greening the path for the initial out-of-Africa dispersal of Homo. Further research on the Kuntila Lake sediments will be necessary to better determine the timing, extent and significance of such biogeographic connection., This study was funded by project CGL2012-30875 of the Ministerio de Economía y Competitividad of Spain and by Internal Funds of the University of Haifa.

Publisher's version (útgefin grein), The CarbFix method was upscaled at the Hellisheiði geothermal power plant to inject and mineralize the plant’s CO2 and H2S emissions in June 2014. This approach first captures the gases by their dissolution in water, and the resulting gas-charged water is injected into subsurface basalts. The dissolved CO2 and H2S then react with the basaltic rocks liberating divalent cations, Ca2+, Mg2+, and Fe2+, increasing the fluid pH, and precipitating stable carbonate and sulfide minerals. By the end of 2017, 23,200 metric tons of CO2 and 11,800 metric tons of H2S had been injected to a depth of 750 m into fractured, hydrothermally altered basalts at >250 °C. The in situ fluid composition, as well as saturation indices and predominance diagrams of relevant secondary minerals at the injection and monitoring wells, indicate that sulfide precipitation is not limited by the availability of Fe or by the consumption of Fe by other secondary minerals; Ca release from the reservoir rocks to the fluid phase, however, is potentially the limiting factor for calcite precipitation, although dolomite and thus aqueous Mg may also play a role in the mineralization of the injected carbon. During the first phase of the CarbFix2 injection (June 2014 to July 2016) over 50% of injected carbon and 76% of sulfur mineralized within four to nine months, but these percentages increased four months after the amount of injected gas was doubled during the second phase of CarbFix2 (July 2016 – December 2017) at over 60% of carbon and over 85% of sulfur. The doubling of the gas injection rate decreased the pH of the injection water liberating more cations for gas mineralization. Notably, the injectivity of the injection well has remained stable throughout the study period confirming that the host rock permeability has been essentially unaffected by 3.5 years of mineralization reactions. Lastly, although the mineralization reactions are accelerated by the high temperatures (>250 °C), this is the upper temperature limit for carbon storage via the mineral carbonation of basalts as higher temperatures leads to potential decarbonation reactions., This publication has been produced with support from the European Commission through the projects CarbFix (EC Project 283148), CO2-React (EC Project 317235), CarbFix2 (EC Project 764760), S4CE (EC Project 764810) in addition to Reykjavik Energy.

Publisher's version (útgefin grein), In the North Volcanic Zone of Iceland, we studied with the greatest possible detail the complete structural architecture and kinematics of the whole Theistareykir Fissure Swarm (ThFS), an N-S-trending, 70 km long active rift. We made about 7500 measurements along 6124 post-Late Glacial Maximum (LGM) extension fractures and faults, and 685 pre-LGM structures. We have collected the data over the last 6 years, through extensive field surveys and with the aid of drone mapping with centimetric resolution. In the southern sector of the study area, extension fractures and faults strike mainly N10°-20°, the opening direction is about N110°, and the dilation amount is in the range 0.1–10 m. In the central sector, faults and extension fractures strike mainly N00-10°, the opening direction is N90-100°, and the dilation amount is 0.1–9 m. In the northern sector, extension fractures and faults strike N30-40°, the opening direction is about N125°, and the dilation amount is 0.1–8 m. The variations in strike are attributable to two processes: the interaction with the WNW-ESE-striking Husavik-Flatey transform fault and Grímsey Oblique Rift (Grímsey lineament), and the structural inheritance of older NNE- to NE-striking normal faults. Most extension fractures show a minor strike-slip component: a systematic right-lateral component can be accounted for by the interaction with the WNW-ESE-striking fault zones and the regional, oblique opening of the rift. We regard dyke propagation as a possible cause for the more complex strike-slip components measured at several other fractures. Cumulated dilation and fracture frequency decrease along the rift with distance away from the Theistareykir volcano, situated in the central sector of the ThFS. This is interpreted as a decrease in the number of dykes that are capable of reaching great distances after being injected from the magma chamber., We wish to acknowledge the reviewers DT and SS for their constructive insights and suggestions on an earlier version of the manuscript. Funding. This work was a contribution to the International Lithosphere Program ? Task Force II. Funding for fieldwork were from ILP and from the MIUR project ACPR15T4_00098 ? Argo3D (http://argo3d.unimib.it/). Furthermore, this study has been carried out in the framework of the Project MIUR ? Dipartimenti di Eccellenza 2018-2022, and European Space Agency project no. 38829. Finally, this effort was also an outcome of GeoVires, the Virtual Reality Lab for Earth Sciences hosted at the Department of Earth and Environmental Sciences, University of Milan Bicocca (Italy). Agisoft Metashape was also acknowledged for photogrammetric data processing.

Publisher's version (útgefin grein), Glacier runoff and melt from volcanic and geothermal activity accumulates in glacier dammed lakes in glaciated areas around the world. These lakes eventually drain, creating hazardous subglacial floods that are usually only confirmed after they exit the glacier and reach local river systems, which can be many tens of kilometres from the flood source. Once in the river systems, they travel rapidly to populated areas. Such delayed detection represents a potentially lethal shortcoming in early-warning. Here we demonstrate how to advance early-warning potential through the analysis of four such floods in a glaciated region of Iceland. By comparing exceptional multidisciplinary hydrological, GPS and seismic ground vibration (tremor) data, we show that array analysis of seismic tremor can be used for early location and tracking of the subglacial flood front. Furthermore the timing and size of the impending flood can be estimated, prior to it entering the river system. Advanced warnings of between 20 to 34 hours are achieved for large (peak discharge of more than 3000 m3/s, accumulation time of ~ 5.25 years) to small floods (peak discharges from 210 to 380 m3/s, accumulation times of ~ 1.3 years) respectively., The data were collected and analyzed within the framework of FutureVolc, which received funding from the European Union’s Seventh Programme for research, technological development and demonstration under grant agreement No. 308377. We thank Martin Möllhoff, Heiko Buxel for technical support, Tómas Jóhannesson for fruitful discussion, Benedikt G. Ófeigsson for assistance with GPS processing and Aoife Braiden and Vilhjálmur Kjartansson for assistance in the field.

Roughness can be used to characterize the morphologies of a lava flow. It can be used to identify lava flow features, provide insight into eruption conditions, and link roughness pattern across a lava flow to emplacement conditions. In this study, we use both the topographic position index (TPI) and the one-dimensional Hurst exponent (H) to derive lava flow unit roughness on the 2014&ndash, 2015 lava field at Holuhraun using both airborne LiDAR and photogrammetric datasets. The roughness assessment was acquired from four lava flow features: (1) spiny lava, (2) lava pond, (3) blocky surface, and (4) inflated channel. The TPI patterns on spiny lava and inflated channels show that the intermediate TPI values correspond to a small surficial slope indicating a flat and smooth surface. Lava pond is characterized by low to high TPI values and forms a wave-like pattern. Meanwhile, irregular transitions patterns from low to high TPI values indicate a rough surface that is found in blocky surface and flow margins. The surface roughness of these lava features falls within the H range of 0.30 &plusmn, 0.05 to 0.76 &plusmn, 0.04. The roughest surface is the blocky, and inflated lava flows appear to be the smoothest surface among these four lava units. In general, the Hurst exponent values in the 2014&ndash, 2015 lava field at Holuhraun has a strong tendency in 0.5, both TPI and Hurst exponent successfully derive quantitative flow roughness.

Publisher's version (útgefin grein), Dissolved Fe (DFe) samples from the GEOVIDE voyage (GEOTRACES GA01, May-June 2014) in the North Atlantic Ocean were analyzed using a seaFAST-pico™ coupled to an Element XR sector field inductively coupled plasma mass spectrometer (SF-ICP-MS) and provided interesting insights into the Fe sources in this area. Overall, DFe concentrations ranged from 0:09 ± 0:01 to 7:8 ± 0:5 nmol L-1. Elevated DFe concentrations were observed above the Iberian, Greenland, and Newfoundland margins likely due to riverine inputs from the Tagus River, meteoric water inputs, and sedimentary inputs. Deep winter convection occurring the previous winter provided iron-to-nitrate ratios sufficient to sustain phytoplankton growth and lead to relatively elevated DFe concentrations within subsurface waters of the Irminger Sea. Increasing DFe concentrations along the flow path of the Labrador Sea Water were attributed to sedimentary inputs from the Newfoundland Margin. Bottom waters from the Irminger Sea displayed high DFe concentrations likely due to the dissolution of Fe-rich particles in the Denmark Strait Overflow Water and the Polar Intermediate Water. Finally, the nepheloid layers located in the different basins and at the Iberian Margin were found to act as either a source or a sink of DFe depending on the nature of particles, with organic particles likely releasing DFe and Mn particle scavenging DFe., This research has been supported by the French National Research Agency ANR GEOVIDE (grant no. ANR-13-BS06-0014), the RPDOC BITMAP (grant no. ANR-12-PDOC-0025-01), the French National Center for Scientific Research (grant no. CNRS-LEFE-CYBER), the LabexMER (grant no. ANR-10-LABX-19), and Ifremer (Institut français de recherche pour l'exploitation de la mer).

Publisher's version (útgefin grein), The Holuhraun–Bárdarbunga (Iceland) eruption lasted approximately 6 months. Magma propagated laterally through a 40 km long dyke, while Bárdarbunga caldera was collapsing. This event was intensely monitored, providing an opportunity to investigate the relationships between eruption dynamics and erupted products. Whole rock and melt inclusion data do not show chemical variations of magma during the eruption. Nevertheless, zoning patterns in clinopyroxene suggest temporal variations of intensive parameters during crystallization. We investigated the chemical zoning of clinopyroxene using a data driven approach, on major and trace elements analyses from lava flow lobes emplaced during the eruption. We applied hierarchical clustering (HC) to identify compositional groups based on major and trace element chemistry. This analysis identifies five compositional groups, which can be associated with specific petrographic features. One cluster represents the chemistry of hourglass sectors, two constitute the oscillatory zoned mantle of the crystals, one cluster corresponds to a seldom present bright rim (in back scattered electron images) in the outer portions of the crystals, and a last one represents most of the outer rims. HC applied to trace elements also identifies five compositional clusters, which highlight progressively more evolved clinopyroxene compositions from the core to the rim of the crystals. Two of the clusters identified with trace elements corresponds to major element clusters. All together the data suggest that the chemical zoning in the inner portions of the clinopyroxene crystals was generated by crystallization in the magma reservoir and interaction between hot magma propagating through the dyke and unerupted magma cooling within the dyke. The fraction of zones produced by interaction with colder portion of the magma residing within the dyke dropped during the eruption, potentially signaling the thermal maturation of the dyke. Some of the analyses reveal that relatively close to the eruption time (i.e., the outer portions of the crystals) the dyke intercepted a lens of low temperature magma with a chemical composition that is distinguishable from the 2014 to 2015 Bárdarbunga eruption. Our approach can provide insights on the evolution of deep processes occurring during long-lasting eruptions by combining the analysis mineral chemistry of erupted products with multiparametric monitoring signals., LC, LP, and GS appreciated the support for fieldwork of the Faculty of Science of the University of Geneva and the access provided by the Vatnajökull National Park. LC and TS received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Program (grant agreement no. 677493 – FEVER). LC and TS acknowledge the support of the Swiss National Science Foundation (grant no. 200021_184632). MP acknowledge the Università degli Studi di Perugia FRB2019 grant titled “ENGAGE – machinE learNinG Applications for Geological problEms.”

Publisher's version (útgefin grein), The volcanic fingerprint on the winter North Atlantic atmospheric circulation and climate is analyzed in six ensemble runs of ECHAM5/MPI-OM covering 800–2000 CE, both for equatorial and Northern Hemisphere (NH) eruptions. Large volcanic eruptions influence climate on both annual and decadal time scales due to dynamic interactions of different climate components in the Earth's system. It is well known that the North Atlantic Oscillation (NAO) tends to shift towards its positive phase during winter in the first 1–2 years after large tropical volcanic eruptions, causing warming over Europe, but other North Atlantic weather regimes have received less attention. Here we investigate the four dominant weather regimes in the North Atlantic: The negative and positive phase of NAO as well as the Atlantic Ridge, Scandinavian blocking. The volcanic fingerprint is detected as a change in the frequency of occurrence and anomalies in the wind and temperature fields as well as in the sea ice cover. We observe a strong significant increase in the frequency of Atlantic Ridge in the second year after equatorial eruptions that precede the NAO+ detected in year 3–5 as a result of a strong zonal wind anomalies in year 1–2. Evidence for a stronger polar vortex is detected in years 12–14 where NAO+ is detected both as a frequency increase and in the wind and temperature fields. A short-term response is also detected 2–4 years after NH eruptions. The longterm signal after NH eruptions indicate a weak polar vortex around a decade after an eruption. Although the signal after NH eruptions is weaker our results stress the need for further studies. The simulated atmospheric response recorded in ECHAM5 after volcanic eruptions suggest a more dynamic response than previously thought. The methodology used can also be applied to other forcing scenario, for example for future climate projections where the aim is to search for a long-term climate signal., Guðlaugsdóttir was supported by the Nordic Volcanological Centre (NordVulk) during this work

Post-print (lokagerð höfundar), Lava flows pose a hazard in volcanic environments and reset ecosystem development. A succession of dated lava flows provides the possibility to estimate the direction and rates of ecosystem development and can be used to predict future development. We examine plant succession, soil development and soil carbon (C) accretion on the historical (post 874 AD) lava flows formed by the Hekla volcano in south Iceland. Vegetation and soil measurements were conducted all around the volcano reflecting the diverse vegetation communities on the lavas, climatic conditions around Hekla mountain and various intensities in deposition of loose material. Multivariate analysis was used to identify groups with similar vegetation composition and patterns in the vegetation. The association of vegetation and soil parameters with lava age, mean annual temperature, mean annual precipitation and soil accumulation rate (SAR) was analysed. Soil carbon concentration increased with increasing lava age becoming comparable to concentrations found on the prehistoric lavas. The combination of a sub-Arctic climate, gradual soil thickening due to input of loose material and the specific properties of volcanic soils allow for continuing accumulation of soil carbon in the soil profile. Four successional stages were identified: initial colonization and cover coalescence (ICC) of Racomitrium lanuginosum and Stereocaulon spp. (lavas 600 years); and highland conditions/retrogression (H/R) by tephra deposition (70−860 years). The long time span of the SC stage indicates arrested development by the thick R. lanuginosum moss mat. The progression from SC into VPD was linked to age of the lava flows and soil depth, which was significantly deeper within the VPD stage. Birch was growing on lavas over 600 years old indicating the development towards birch woodland, the climax ecosystem in Iceland., The Icelandic Research Fund, Rannís, Grant of Excellence no. 152266-052 (Project: EMMIRS).

Publisher's version (útgefin grein), Meaningful forecasting of the atmospheric concentration and ground accumulation of volcanic ash during explo-sive eruptions requires detailed knowledge of the eruption source parameters. However, due to the large uncer-tainties in observations and limitations of current models used to make inferences from these, monitoring anongoing eruption and quantifying the mass eruption rate in real-time is a considerable challenge. Within theEU supersite project“FutureVolc”, an integrated approach has been applied to develop a quasi-autonomousmulti-parameter system, denoted“REFIR”, for monitoring volcanic eruptions in Iceland and assessing the erup-tion massflow rate by inverting the plume height information and taking account of these uncertainties. REFIRhas the capability to ingest and process streaming plume-height data provided by a multitude of ground basedsensors, including C–and X-band radars and web-cam based plume height tracking systems. These observationaldata are used with a suite of plume models that also consider the current wind and other atmospheric conditions,providing statistically assessed best estimates of plume height and mass eruption rate. Provided instrumentaldata is available, near real-time estimates are obtained (the delay corresponding to the scan rate of data-providing instruments, presently of the order of minutes). Using the Hekla 2000, and Eyjafjallajökull 2010 erup-tions in Iceland, the potential of REFIR is demonstrated and discussed through application to three scenarios. Thesystem has been developed to provide maximumflexibility. A setup script assists the user in adapting to localconditions, allowing implementation of REFIR for any volcanic eruption site worldwide. REFIR is designed to beeasily upgradable, allowing future extension of monitoring networks, learning from new events, and incorpora-tion of new technologies and model improvements. This article gives an overview of the basic structure, modelsimplemented, functionalities and the computational techniques of REFIR., The development of REFIR has been part of the FUTUREVOLC supersite project and was funded by the European Union's Seventh Programme for research, technological development and demonstration under grant agreement No 308377. TD's work was also funded by the project EVER-EST, as part of the EU's Horizon 2020 research and innovation programme under grant agreement no 674907.

Publisher's version (útgefin grein), The Holocene climatic optimum was a period 8–5 kyr ago when annual mean surface temperatures in Greenland were 2–3°C warmer than present-day values. However, this warming left little imprint on commonly used temperature proxies often used to derive the climate forcing for simulations of the past evolution of the Greenland ice sheet. In this study, we investigate the evolution of the Greenland ice sheet through the Holocene when forced by different proxy-derived temperature histories from ice core records, focusing on the effect of sustained higher surface temperatures during the early Holocene. We find that the ice sheet retreats to a minimum volume of ~0.15–1.2 m sea-level equivalent smaller than present in the early or mid-Holocene when forcing an ice-sheet model with temperature reconstructions that contain a climatic optimum, and that the ice sheet has continued to recover from this minimum up to present day. Reconstructions without a warm climatic optimum in the early Holocene result in smaller ice losses continuing throughout the last 10 kyr. For all the simulated ice-sheet histories, the ice sheet is approaching a steady state at the end of the 20th century., This work is supported by the Danish National Research Foundation under the Centre for Ice and Climate, University of Copenhagen and Villum Investigator Project IceFlow. Brice Noël and Michiel van den Broeke (IMAU, Utrecht University) are thanked for providing the RACMO2.3 Greenland SMB, precipitation and temperature data. B. Vinther is thanked for providing the Holocene accumulation reconstruction for the GRIP site. We are grateful for computing resources provided by the Danish Center for Climate Computing, a facility build with support of the Danish e-Infrastructure Corporation and the Niels Bohr Institute. Development of PISM is supported by NASA grants NNX13AM16G and NNX13AK27G. We thank the anonymous reviewers and Ralf Greve for their helpful suggestions which substantially improved the paper.

Publisher's version (útgefin grein), Lava flow thicknesses, volumes, and effusion rates provide essential information for understanding the behavior of eruptions and their associated deformation signals. Preeruption and posteruption elevation models were generated from historical stereo photographs to produce the lava flow thickness maps for the last five eruptions at Hekla volcano, Iceland. These results provide precise estimation of lava bulk volumes: V1947–1948 = 0.742 ± 0.138 km3, V1970 = 0.205 ± 0.012 km3, V1980–1981 = 0.169 ± 0.016 km3, V1991 = 0.241 ± 0.019 km3, and V2000 = 0.095 ± 0.005 km3 and reveal variable production rate through the 20th century. These new volumes improve the linear correlation between erupted volume and coeruption tilt change, indicating that tilt may be used to determine eruption volume. During eruptions the active vents migrate 325–480 m downhill, suggesting rough excess pressures of 8–12 MPa and that the gradient of this excess pressure increases from 0.4 to 11 Pa s−1 during the 20th century. We suggest that this is related to increased resistance along the eruptive conduit., Icelandic Research Fund. Grant Number: 152266‐052

Contiguous sampling of ice spanning key intervals of the deglaciation from the Greenland ice cores of NGRIP, GRIP and NEEM has revealed three new silicic cryptotephra deposits that are geochemically similar to the well‐known Borrobol Tephra (BT). The BT is complex and confounded by the younger closely timed and compositionally similar Penifiler Tephra (PT). Two of the deposits found in the ice are in Greenland Interstadial 1e (GI‐1e) and an older deposit is found in Greenland Stadial 2.1 (GS‐2.1). Until now, the BT was confined to GI‐1‐equivalent lacustrine sequences in the British Isles, Sweden and Germany, and our discovery in Greenland ice extends its distribution and geochemical composition. However, the two cryptotephras that fall within GI‐1e ice cannot be separated on the basis of geochemistry and are dated to 14358 ± 177 a b2k and 14252 ± 173 a b2k, just 106 ± 3 years apart. The older deposit is consistent with BT age estimates derived from Scottish sites, while the younger deposit overlaps with both BT and PT age estimates. We suggest that either the BT in Northern European terrestrial sequences represents an amalgamation of tephra from both of the GI‐1e events identified in the ice‐cores or that it relates to just one of the ice‐core events. A firm correlation cannot be established at present due to their strong geochemical similarities. The older tephra horizon, found within all three ice‐cores and dated to 17326 ± 319 a b2k, can be correlated to a known layer within marine sediment cores from the North Iceland Shelf (ca. 17179‐16754 cal a BP). Despite showing similarities to the BT, this deposit can be distinguished on the basis of lower CaO and TiO2 and is a valuable new tie‐point that could eventually be used in high‐resolution marine records to compare the climate signals from the ocean and atmosphere., European Research Council (TRACE project) under the European Union's Seventh Framework Programme (FP7/2007‐2013)/ERC. Grant Number: 259253 EU framework programme (FP7/2007‐2013)/ERC. Grant Number: 610055 EU COST INTIMATE action. Grant Number: ES0907

The 6-month long eruption at Holuhraun (August 2014–February 2015) in the Bárðarbunga-Veiðivötn volcanic system was the largest effusive eruption in Iceland since the 1783–1784 CE Laki eruption. The lava flow field covered ~84 km2 and has an estimated bulk (i.e., including vesicles) volume of ~1.44 km3. The eruption had an average discharge rate of ~90 m3/s making it the longest effusive eruption in modern times to sustain such high average flux. The first phase of the eruption (August 31, 2014 to mid-October 2014) had a discharge rate of ~350 to 100 m3/s and was typified by lava transport via open channels and the formation of four lava flows, no. 1–4,which were emplaced side by side. The eruption began on a 1.8 km long fissure, feeding partly incandescent sheets of slabby pāhoehoe up to 500 m wide. By the following day the lava transport got confined to open channels and the dominant lava morphology changed to rubbly pāhoehoe and ‘a’ā. The latter became the dominating morphology of lava flows no. 1–8. The second phase of the eruption (Mid-October to end November) had a discharge of ~100–50 m3/s. During this time the lava transport system changed, via the formation of a b1 km2 lava pond ~1 km east of the vent. The pond most likely formed in a topographical low created by a the pre-existing Holuhraun and the newHoluhraun lava flow fields. This pond became themain point of lava distribution, controlling the emplacement of subsequent flows (i.e. no. 5–8). Towards the end of this phase inflation plateaus developed in lava flowno. 1. These inflation plateaus were the surface manifestation of a growing lava tube system, which formed as lava ponded in the open lava channels creating sufficient lavastatic pressure in the fluid lava to lift the roof of the lava channels. This allowed new lava into the previously active lava channel lifting the channel roof via inflation. The final (third) phase, lasting from December to end-February 2015 had a mean discharge rate of ~50 m3/s. In this phase the lava transport was mainly confined to lava tubes within lava flows no. 1–2, which fed breakouts that resurfaced N19 km2 of the flow field. The primary lava morphology from this phase was spiny pāhoehoe, which superimposed on the ‘a’ā lava flows no. 1–3 and extended the entire length of the flow field (i.e. 17 km). Thismade the 2014–2015 Holuhraun a paired flow field,where both lava morphologies had similar length. We suggest that the similar length is a consequence of the pāhoehoe is fed from the tube systemutilizing the existing ‘a’ā lava channels, and thereby are controlled by the initial length of the ‘a’ā flows., The work was financed with crisis response funding from the Icelandic Government along with European Community's Seventh Framework Programme Grant No. 308377 (Project FUTUREVOLC) and along with the Icelandic Research fund, Rannis, Grant of Excellence No. 152266-052 (Project EMMIRS). Furthermore, Vinur Vatnajökuls are thanked for support.

A large rockslide was released from the inner Askja caldera into Lake Askja, Iceland, on 21 July 2014. Upon entering the lake, it caused a large tsunami that traveled about ∼3 km across the lake and inundated the shore with vertical runup measuring up to 60–80 m. Following the event, comprehensive field data were collected, including GPS measurements of the inundation and multibeam echo soundings of the lake bathymetry. Using this exhaustive data set, numerical modeling of the tsunami has been conducted using both a nonlinear shallow water model and a Boussinesq-type model that includes frequency dispersion. To constrain unknown landslide parameters, a global optimization algorithm, Differential Evolution, was employed, resulting in a parameter set that minimized the deviation from measured inundation. The tsunami model of Lake Askja is the first example where we have been able to utilize field data to show that frequency dispersion is needed to explain the tsunami wave radiation pattern and that shallow water theory falls short. We were able to fit the trend in tsunami runup observations around the entire lake using the Boussinesq model. In contrast, the shallow water model gave a different runup pattern and produced pronounced offsets in certain areas. The well-documented Lake Askja tsunami thus provided a unique opportunity to explore and capture the essential physics of landslide tsunami generation and propagation through numerical modeling. Moreover, the study of the event is important because this dispersive nature is likely to occur for other subaerial impact tsunamis., Nordic Centre of Excellence on Resilience and Societal Security (NORDRESS) Research Council of Norway -231252 Icelandic Avalanche and Landslide Fund Vatnajokull National Park

The evolution of hydrothermal alteration in glassy and variably palagonitized tuff, erupted as tephra in 1963 – 1964 on Surtsey, an island built in the offshore extension of Iceland’s southeast rift zone, is documented through a comparative petrographic study of samples from drill cores recovered in 1979 and 2017. Time-lapse alteration within the low-temperature meteoric to seawater dominated hydrothermal system of the volcano is characterized in terms of secondary mineral contents, alteration rates and alteration style with depth. Between 1979 and 2017 palagonitization and cementation by secondary minerals has progressed into previously poorly altered parts of the system, leading to increased consolidation of the basaltic tephra. Alteration rates range between 1.05 – 42.5 μm∙yr-1 for palagonitization of glass and 0.4 – 8.33 μm∙yr-1 for pseudomorphic olivine replacement by clay minerals over a temperature interval of 47 – 140°C. Five distinct zones of alteration style, distinguished through alteration mineralogy, development of authigenic phases over time, as well as degree of alteration are described. Alteration of basaltic tephra at Surtsey volcano is defined by an early stage of phillipsite and clay mineral formation, followed by a later stage of analcime and tobermorite formation as well as replacement of phillipsite below the water table in zone 2 between 65.4 and 138.4 m. Only minor advancement of alteration is detected in zone 3 between 138.4 – 150.3 m depth, where the primary tephra remains largely unpalagonitized and unconsolidated. In contrast, from 1979 to 2017 alteration has increased between 150.3 – 177.8 m depth, in zone 4, leading to rapid and extensive glass and olivine alteration. The quantification of these time-lapse hydrothermal alteration processes at Surtsey provides an important reference for studies of the evolution of young oceanic islands hosting hydrothermal systems., International Continental Scientific Drilling Program (ICDP); Icelandic Research Fund, ICF-RANNÍS; Bergen Research Foundation and K.G. Jebsen Centre for Deep Sea Research at the University of Bergen, Norway; German Research Foundation; DiSTAR, Federico II, University of Naples, Federico II, Italy; University of Utah, USA; Reykjavík Energy; Landsvirkjun, Pre-print

Publisher's version (útgefin grein), Lake Myvatn, Iceland, is one of the most biologically productive lakes in the northern hemisphere, despite seasonal ice cover. Hydrothermal and groundwater springs make up the dominant source to this lake, and we investigate their Mg isotope ratio to assess the effect of mid-ocean ridge hydrothermal springs, which are the primary modern sink of seawater magnesium. We also examine a time series in the only outflow from this lake, the Laxa River, to assess the effects of seasonal primary productivity on Mg isotopes. In the hydrothermal waters, there is a clear distinction between cold waters (largely unfractionated from primary basalt) and relatively hot waters, which exhibit over 1‰ fractionation, with consequences for the oceanic mass balance if the hydrothermal removal of Mg is not fully quantitative. The outflow Mg isotopes are similar to basalts (δ26Mg = −0.2 to −0.3) during winter but reach a peak of ∼0‰ in August. This fractionation corresponds to calcite precipitation during summer in Lake Myvatn, preferentially taking up light Mg isotopes and driving the residual waters isotopically heavy as observed, meaning that overall the lake is a CO2 sink., PP and the analyses were funded by NERC grant NE/I020571/2, and PP and MM are also supported by ERC Consolidator grant 682760 CONTROLPASTCO2.

Pre-print (óritrýnt handrit), Oceanic crust is a major transport medium of water into the mantle wedge and the convecting mantle. Yet, the water content of the oceanic crust remains uncertain. Active geothermal systems situated at on-land spreading centers provide a unique opportunity to study the hydration of the oceanic crust, with well constrained systems and boreholes reaching depths of >4 km. Here, we present hydrogen isotope data of geothermal fluids and altered basalt for three Icelandic geothermal systems: the meteoric water fed system at Krafla and the seawater fed systems at Reykjanes and Surtsey. The bulk rock δD values of altered and hydrated basalts from these localities, which exhibit significantly higher water contents (up to 8.9 wt.%) than magmatic (non-hydrated) basalts, vary greatly from −125 to −96 at Krafla, from −80 to −46 at Reykjanes and from −78 to −46 at Surtsey. The corresponding fluids have δD values of −84.1 to −81.1 at Krafla, −23.1 to −14.9 at Reykjanes and +2.1 to +4.3 at Surtsey. Comparison of isotope modeling results to the natural data reveals that hydration of the Icelandic crust and corresponding hydrogen isotopic characteristics are controlled by (1) the isotope composition of the source fluid, (2) isotope fractionation between the aqueous geothermal fluids and the alteration minerals formed, and (3) the type and quantity of alteration minerals formed. These factors in turn depend on the extent of fluid-rock interaction and temperature. Using the same modeling approach and expanding it to datasets available for the oceanic crust, we assessed the hydration state and δD values of the oceanic crust as a function of depth. We show that 1400 to 1650 Tg H2O/yr is added to the igneous oceanic crust upon alteration by seawater and that the upper part (, This project was financially supported by NordVulk, the International Continental Scientific Drilling Program (ICDP) through a grant to the SUSTAIN project, and the Icelandic Research Fund (project number: 163083-051). SAH acknowledges support from the Icelandic Research Fund (project number: 196139-051). HS Orka and Landsvirkjun kindly provided access to the drill cuttings. J. Cullen, T. Larson, R. Ólafsdóttir and Á.E. Sveinbjörnsdóttir are thanked for assistance during sample preparation and data acquisition. BIK is particularly grateful of being part of this project as without the project-related lab work she would have never met her future husband E.W. Marshall IV. We thank four anonymous reviewers for their constructive comments and suggestions to an earlier version of this manuscript. Louis Derry is thanked for careful editorial handling of this study.

Publisher's version (útgefin grein), Arctic hotspots, local areas of high biodiversity, are potential key sites for conservation of Arctic biodiversity. However, there is a need for improved understanding of their long-term resilience. The Arctic hotspot of Ringhorndalen has the highest registered diversity of vascular plants in the Svalbard archipelago, including several remarkable and isolated plant populations located far north of their normal distribution range. Here we analyze a lake sediment core from Ringhorndalen for sedimentary ancient DNA (sedaDNA) and geochemical proxies to detect changes in local vegetation and climate. Half of the plant taxa appeared already before 10,600 cal. yr BP, indicating rapid colonization as the ice retreated. Thermophilous species had a reoccurring presence throughout the Holocene record, but stronger signal in the early than Late Holocene period. Thus, thermophilous Arctic plant species had broader distribution ranges during the Early Holocene thermal maximum c. 10,000 cal. yr BP than today. Most of these thermophilous species are currently not recorded in the catchment area of the studied lake, but occur locally in favourable areas further into the valley. For example, Empetrum nigrum was found in >40% of the sedaDNA samples, whereas its current distribution in Ringhorndalen is highly restricted and outside the catchment area of the lake. Our findings support the hypothesis of isolated relict populations in Ringhorndalen. The findings are also consistent with main Holocene climatic shifts in Svalbard identified by previous studies and indicate an early warm and species-rich postglacial period until c. 6500 cal. yr BP, followed by fluctuating cool and warm periods throughout the later Holocene., The core-samplingfield campaign, subsequent sub-sampling ofsediments and macrofossils, ITRAX-scans, and radiocarbon datingwere funded by the Svalbard Environmental Protection Fund(project 16/35 to WRF). Financial support for molecular analysisandfield work was provided by the Svalbard Environmental Pro-tection Fund (project 14/118 to PBE) and Jan Christensen’sendowment (to LHV). IGA and PDH acknowledge support from theResearch Council of Norway (Grant 250963:“ECOGEN”). We thankJohannes Sand Bolstad forfield assistance, Kari Klanderud forproject administration, the wider ECOGEN research group inTromsø, including Dilli Rijal for pooling and cleaning of the PCRproducts and Youri Lammers for helping with bioinformatic ana-lyses and reference libraries. Bioinformatic analyses were per-formed on the Abel Cluster, owned by the University of Oslo andUninett/Sigma2, and operated by the Department for ResearchComputing at USIT, the University of Oslo IT-department.http://www.hpc.uio.no/. We thank Marie-Louise Siggaard-Andersen forassistance with the ITRAX-scanning of the sediment core as well asDr. Skafti Brynj olfsson and Dr. Marc Macias-Fauria for collaborationin the field.

Publisher's version (útgefin grein), Large volume effusive eruptions with relatively minor observed precursory signals are at odds with widely used models to interpret volcano deformation. Here we propose a new modelling framework that resolves this discrepancy by accounting for magma buoyancy, viscoelastic crustal properties, and sustained magma channels. At low magma accumulation rates, the stability of deep magma bodies is governed by the magma-host rock density contrast and the magma body thickness. During eruptions, inelastic processes including magma mush erosion and thermal effects, can form a sustained channel that supports magma flow, driven by the pressure difference between the magma body and surface vents. At failure onset, it may be difficult to forecast the final eruption volume; pressure in a magma body may drop well below the lithostatic load, create under-pressure and initiate a caldera collapse, despite only modest precursors., The research presented here has benefitted from extended visits of FS during a sabbatical term to, and discussion with scientists at, the University of Leeds, ISTerre University of Savoie Mont-Blanc, USGS Cascades Volcano Observatory, and Geological Survey of Japan. We acknowledge reviews by Philip Benson and Luca Caricchi that helped to significantly improve the paper, as well as reviews of an early version of the paper by two anonymous reviewers. Financial support from the H2020 project EUROVOLC funded by the European Commission is acknowledged (grant number 731070). F.S. acknowledges support from the University of Iceland Research Fund, and R.G. acknowledges partial support through NSF grant EAR-1464546. Fissure swarms, central volcanoes and caldera outlines shown in Fig. 1 are reproduced from publications referred to (refs. 42,76) with permissions from Elsevier, and we acknowledge the use of ArticDEM (ref. 77) to plot surface and ice topography shown in Fig. 1. COMET is the NERC Centre for the Observation and Modelling of Earthquakes, Volcanoes and Tectonics, a partnership between UK Universities and the British Geological Survey.

Publisher's version (útgefin grein), Arctic precipitation is predicted to increase in the coming century, due to a combination of enhanced northward atmospheric moisture transport and local surface evaporation from ice-free seas. However, large model uncertainties, limited long-term observations, and high spatiotemporal variability limit our understanding of these mechanisms, emphasizing the need for paleoclimate records of precipitation changes. Here we use lipid biomarkers in lake sediments to reconstruct precipitation seasonality in northern Spitsbergen, Svalbard. We measured the hydrogen isotopic ratios (δ2H) of n-alkanoic acids (C20–C30) from sedimentary leaf waxes in lake Austre Nevlingen, Spitsbergen. We interpret δ2H values of mid-chain (C22) and long-chain (C28) n-alkanoic acids to represent δ2H of lake and soil water, respectively. Austre Nevlingen lake water δ2H reflects amount-weighted mean annual precipitation δ2H. In contrast, soil water is mostly recharged by summer rainfall, and therefore reflects δ2H values of summer precipitation. Austre Nevlingen leaf wax δ2H values are 2H-depleted in the Early Holocene, suggesting high winter precipitation amounts. This coincides with high summer insolation, strong Atlantic water advection and reduced spring sea-ice cover in surrounding waters. Winter precipitation continued to dominate until c. 6 cal. kyr BP. After 6 cal. kyr BP, the trend in the biomarker record is not as clear. This could be related to colder conditions causing longer duration of seasonal lake-ice cover, thereby influencing the precipitation seasonality registered by the lake water. The Austre Nevlingen record suggests a close relationship between precipitation seasonality and regional ocean surface conditions, consistent with simulations suggesting that Arctic winter sea-ice loss will lead to increased local evaporation., Fieldwork, radiocarbon dates, and laboratory analyses were funded by the Carlsberg Foundation (grant number CF14-0756 to AS), the Nansen Foundation (to AS), and the Svalbard Environmental Protection Fund (grant number 17/101 to AS and 17/114 to LA). The 2015 fieldwork was partly funded by the University Centre in Svalbard (UNIS) Research Fund (grant to ÓI). Laboratory analyses and technician support were also funded by National Science Foundation Grant (grant number 1652274 to EKT) and a UB Center for Undergraduate Research and Creative Activities Grant (to SD). We thank Sveinn Brynjólfsson and Sara Mollie Cohen for field assistance, Mike Retelle for providing field equipment, Marie-Louise Siggaard-Andersen for assistance with the ITRAX-scanning, and Alexandra Rouillard for macrofossil identification and data discussion. Finally, we thank Willem van der Bilt and one anonymous reviewer for constructive comments that improved this manuscript.

Publisher's version (útgefin grein), Agriculture has been practiced in Iceland since settlement (landnám; AD 877). This has caused changes in vegetation communities, soil erosion, desertification and loss of carbon stocks. Little data exist regarding vegetation and ecosystems in the Icelandic highland before landnám and therefore the impact of land use over time is poorly understood. The objectives of the study are to examine the timing, nature and causes of land degradation in the highland of Northwest Iceland. Specifically, to determine the resilience of the pre-landnám highland environment to disturbances (i.e. climate cooling and volcanism) and whether land use pressure was of sufficient magnitude to facilitate ecosystem change. A sediment core was taken from the highland lake Galtaból. A chronology for the core was constructed using known tephra layers and radiocarbon dated plant macrofossils. Pollen analysis (vegetation), coprophilous fungal spores (proxy for grazing), and sediment properties (proxies for erosion) were used to provide a high-resolution, integrated vegetation and paleoenvironmental reconstruction. The pre-landnám environment showed resilience to climate cooling and repeated tephra fall. Soon after landnám the vegetation community changed and instability increased, indicated by changes in sediment properties. The pollen and spore record suggest introduction of grazing herbivores into the area after landnám. Following landnám, indicators of soil erosion appear in the sediment properties. Intensification of soil erosion occurred during the 17th century. The Galtaból record clearly demonstrates what can happen in landscapes without adequate management of natural resources and underestimation of landscape sensitivity. Introduction of land use resulted in changes in vegetation communities, loss of resilience and onset of increased soil erosion. Paleoenvironmental reconstructions may inform future decisions on management of the highland by providing baselines for natural variability in the pre-landnám environment., The authors would like to thank Þorsteinn Jónsson and Höskuldur Þorbjarnarson for assistance in the field. Jessica Lynn Till is thanked for proofreading the manuscript. We would like to thank Leone Tinganelli for his work on milling sediment samples for C and N analysis. The Blönduvirkjun hydropower plant kindly hosted us during fieldwork. The authors would like to thank three anonymous reviewers for their valuable comments and suggestions. The research was funded by the Landsvirkjun Energy Research Fund, the University of Iceland Research Fund, and the Icelandic Research Fund (grant no. 141842-051 ).

Publisher's version (útgefin grein)., The long-term supply sustainability of copper, zinc and lead was assessed. Copper will not run into physcal scarcity in the future, but increased demand and decreased resource quality will cause significant price increases. The copper price is suggested to increase significantly in the coming decades. A similar situation applies for zinc and lead with soft scarcity and increased prices for zinc. The total supply of copper reaches a maximum 2030–2045, zinc 2030–2050 and lead 2025-2030. The copper supply per person and year and decline after 2130, and the copper stock-in-use reaches a maximum in 2050 and decline afterwards. The zinc supply per person per year reach a maximum in 2100 and decline after 2100, and the zinc stock-in use shows a similar pattern. The lead supply per person reach a plateau in 1985, and decline after 2070, whereas the lead stock-in-use reach a plateau in 2080 and decline after 2100. For copper, zinc and lead, scarcity will mainly be manifested as increased metal price, with feedbacks on demand. The predicted price increase will cause recycling to increase in the future. The supply situation for copper would be much improved if the recycling of copper could be strongly promoted through policy means, as well as it would work well to limit the price increases predicted under business-as-usual. Considering the importance of these metals for society, it is essential to set adequate policies for resource efficiency and resource conservation for society., This study contributed to the SimRess project (Models, potential andlong-term scenarios for resource efficiency),funded by the GermanFederal Ministry for Environment and the German EnvironmentalProtection Agency (FKZ 3712 93 102). Dr. Ullrich Lorenz is projectofficer at the German Environmental Protection Agency (UBA). Onbehalf of all authors, the corresponding author states that there is noconflict of interest.

Publisher's version (útgefin grein)., To gain insights into crystal–melt separation processes during basalt differentiation, we have studied an 8-m-thick pāhoehoe lava lobe from the Hafnarhraun lava flow field in SW Iceland. The lobe has abundant melt segregations, porous cylindrical and sheet-like structures, generally interpreted as separated residual melts of a lava lobe. We divide these melt segregations into three types based on morphology and composition: vesicle cylinders (VC), type 1 horizontal vesicle sheets (HVS1), and type 2 horizontal vesicle sheets (HVS2). Remarkably, the studied VC are not simple residual melts generated by fractional crystallization, but their composition points to removal of plagioclase from the parental lava. HVS1 resemble VC, but have fractionated more olivine (ol) + plagioclase (plg) ± augite and have lost most, if not all, of their olivine phenocrysts. HVS2 are Fe-rich and evolved, corresponding to residual melts after 50–60% fractional crystallization of the lobe. We suggest that the Hafnarhraun VC formed in a two-stage process. Firstly, VC forming residual melt and vapor detached as rising diapirs from ol+plg+melt+vapor mush near the lava base, and later, these VC diapirs accumulated ol phenocrysts and minor plg microphenocrysts in the lava core. HVS1 represent accumulations of VC to the viscous base of the solidifying upper crust of the lobe, and HVS2 formed as evolved vapor-saturated residual melts seeped into voids within the upper crust. Such vapor-aided differentiation, here documented for the Hafnarhraun lava, may also apply to shallow crustal magma storage zones, contributing to the formation of evolved basalts., The Nordic Volcanological Center funded this work 2015–2017. We thank Robert A. Askew and Leó Kristjánsson for the aid in sampling, Atli Hjartarson and Guðmundur H. Guðfinnsson for the help in sample preparation and microprobe analyses, and Richard J. Brown for the editorial handling. Comments from Kaisa Nikkilä, Scott Rowland, and anonymous reviewer significantly improved the manuscript. Funding information: Open access funding provided by University of Helsinki including Helsinki University Central Hospital.

Publisher's version (útgefin grein)., New highway exposures and drilling reveal the stratigraphy and structure of the Middle Swedish end-moraine zone west of Billingen, Sweden. The material in the end moraines is primarily glaciomarine clay of Younger Dryas age that was deposited as varved clay in front of the retreating glacier and then pushed glaciotectonically to form push moraines during minor ice-margin oscillations during overall retreat during the Younger Dryas cold event. The moraines are composed of deformed and remobilized clay with some clayey diamicton and penecontemporaneously deposited and deformed sand. Between the moraines lie ‘intermoraine flats,’ composed of undeformed varved clay of Younger Dryas age and surface sands of Younger Dryas to early Holocene age. Based on estimations of moraine volume, sedimentation rate and ice-margin retreat rates, we calculate the overall ice-margin retreat and end-moraine construction to span 350–800 years within the Younger Dryas. Because the number of moraines in the Middle Swedish end-moraine zone varies across Sweden, we regard the individual oscillations west of Billingen to be driven by local physical and glaciologic factors rather than ice-sheet wide climate drivers. The study area is also the location of the early and final drainages of the Baltic Ice Lake. The final drainage of the Baltic Ice Lake took place several decades after the youngest moraine was formed. We consider it likely that the earlier, Allerød drainage of the Baltic Ice Lake (BIL) also took place at Billingen, despite the lack of clear local stratigraphic evidence. However, based on our model, a retreat driven solely by climate would not have exposed the outlet at Billingen, and we propose a dynamic break-up of the ice-margin likely centered on Valle Härad that was driven by the head difference between the BIL and the sea., This project was financed by the Swedish Geological Survey , grants SGU 60-1668/2008 and SGU 61-1538/2010 . Special thanks for help in the field to Ylva Ståhl and Nina Vallendin. Tore Påsse, Svante Björck and Bo Strömberg have helped tremendously over the years with discussion and material, and we thank them. We thank Matthew Bennett and an anonymous reviewer for providing helpful comments on the first version of the manuscript. Finally, the late Gustav Lind provided essential and glad help with the geophysical measurements in the Skara and Skånings-Åsaka end moraines.

Publisher's version (útgefin grein)., Studies of short-lived radiogenic isotope systems and noble gas isotopic compositions of plume-derived rocks suggest the existence of primordial domains in Earth's present-day mantle. Tungsten-182 anomalies together with high 3He/4He in Phanerozoic rocks from large igneous provinces and ocean island basalts demonstrate the preservation of early-formed (within the first 60 Ma of solar system history) mantle domains tapped by modern mantle plumes. It has proven difficult to link the evidence for primordial domains with geochemical evidence for more recent processes, such as recycling. The Greenland-Iceland plume system, starting with eruptions of the Paleocene North Atlantic Igneous Province, is later manifested in the mid-Miocene to modern volcanic products of Iceland. Here, we report Pb isotopic compositions, μ182W (deviations in 182W/184W of a sample from a laboratory reference standard in parts per million), and 3He/4He, as well as highly siderophile element concentrations and Re-Os isotopic systematics of basaltic samples erupted at different times during the ~60 Ma history of the Greenland-Iceland plume. Paleocene samples from Greenland, representing the early stage of the mantle plume, are characterized by variable 3He/4He ranging from 7 to 48 R/RA (measured 3He/4He normalized to the atmospheric ratio) and an average μ182W of −4.0 ± 3.6 (2SD), within modern upper mantle-like values of 0 ± 4.5. The basalts from Iceland can be divided into two groups based on their Pb isotope compositions. One group, consisting mostly of Miocene basalts, is characterized by 206Pb/204Pb ranging from ~18.4 to 18.5, 3He/4He ranging from 17.8 to 40.2 R/RA, and μ182W values ranging from +1.7 to −9.1 ± 4.5. The other group, consisting mainly of Pleistocene and Holocene basalts, is characterized by higher 206Pb/204Pb, ranging from ~18.7 to 19.2, 3He/4He ranging from 7.9 to 25.7 R/RA, and μ182W values ranging from −0.6 to −11.7 ± 4.5. Collectively, the Greenland-Iceland suite examined requires mixing between a minimum of three mantle source domains characterized by distinct Pb-He-W isotopic compositions, in order to account for this range of isotopic data. The temporal changes in the isotopic data for these rocks appear to track the dominant contributing plume components as the system evolved. One of the domains is indistinguishable from the ambient upper oceanic mantle and contributed substantial material throughout the time progression. The other two domains are most likely primordial reservoirs that underwent limited de-gassing. Given the negative μ182W values in some rocks, one of these domains likely formed within the first 60 Ma of solar system history and is a major contributor to the youngest basalts. The isotopic characteristics of Greenland-Iceland plume-derived rocks reveal episodic changes in the source component proportions., This study was supported by NSF grant EAR-1624587 (to RJW and AMP). AMP acknowledges FWF grant V659-N29 . MJ acknowledges NSF grant EAR-1624840 , and MK acknowledges OCE-1259218 . We would like to thank Lotte M. Larsen and Asger K. Pedersen for providing the West Greenland samples, and Bernard Marty for the samples from East Greenland. We thank Catherine Chauvel for the editorial handling and Rita Parai, Dominique Weis, David Graham and an anonymous reviewer for the helpful and constructive comments on this and an earlier version of the manuscript.

Publisher's version (útgefin grein), In the beginning of December 2017, Mt. Agung eruption powered down to minor ash emissions and on the middle of December, aerial photographs of the crater were taken by Indonesia Centre of Volcanology and Geological Hazard Mitigation (PVMBG) showing a steadily growing lava occupying approximately one third of the crater. 3D digital elevation model (DEM) of crater were created by PVMBG during and before the eruption, corresponded to lava volume around 2 x 10−2 km3 has been filled the crater. Here we present a method for deriving thermal model within the lava during eruption on 8 and 9 December 2017 using observations from multi infrared satellite SENTINEL 2A and Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). We use Thermal Eruption Index (TEI) based on the Shortwave infrared (SWIR) on SENTINEL 2A and Thermal Infrared (TIR) on ASTER, allowing us to differentiate thermal domain within the lava. This study has successfully produced model of sub-pixel temperature (Th), radiant flux (Φrad) and crust thickness model of lava (Δh). The subpixel temperature and radiant flux during the eruption is in the range 655 to 975 °C and 179 MW respectively. The crust thickness model of the lava in the range of 9 to 14 m and the total volume of lava crust during this period is estimated at 3 x 10−3 km3. The combination of infrared satellite remote sensing data shows a potential for fast and efficient classification of difference thermal domains and derive thermal model of lava., The first author has been supported by the Indonesia Endowment Fund for Education (LPDP), Institute of Earth Science and Vinir Vatnajökuls during his PhD project.

Publisher's version (útgefin grein), Abiotic formation of n-alkane hydrocarbons has been postulated to occur within Earth's crust. Apparent evidence was primarily based on uncommon carbon and hydrogen isotope distribution patterns that set methane and its higher chain homologues apart from biotic isotopic compositions associated with microbial production and closed system thermal degradation of organic matter. Here, we present the first global investigation of the carbon and hydrogen isotopic compositions of n-alkanes in volcanic-hydrothermal fluids hosted by basaltic, andesitic, trachytic and rhyolitic rocks. We show that the bulk isotopic compositions of these gases follow trends that are characteristic of high temperature, open system degradation of organic matter. In sediment-free systems, organic matter is supplied by surface waters (seawater, meteoric water) circulating through the reservoir rocks. Our data set strongly implies that thermal degradation of organic matter is able to satisfy isotopic criteria previously classified as being indicative of abiogenesis. Further considering the ubiquitous presence of surface waters in Earth's crust, abiotic hydrocarbon occurrences might have been significantly overestimated., This work became possible through DFG grant FI 948/8-1.