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Glacial outburst floods (jökulhlaups) have been a significant driver of landscape evolution, environmental change, and geohazards throughout the Quaternary. Iceland experiences more frequent jökulhlaups than nearly anywhere else on Earth, though most research focuses on subglacial volcanogenic floods that drain across outwash plains. Abundant geomorphologic evidence exists for largescale jökulhlaups that drained along the modern-day course of the Hvítá River in southwestern Iceland during early Holocene deglaciation, originating from ice-dammed Glacial Lake Kjölur; yet only one previous publication has investigated these events. This study uses a combination of field mapping and remote sensing to identify new jökulhlaup geomorphologic evidence along the Hvítá River, including erosional landforms such as scoured bedrock, anastomosing channel networks, cataracts, and canyons, and depositional features such as boulder bars and channel infill. We synthesize new findings with previously reported work to: 1) present an updated geomorphologic map of Hvítá jökulhlaup evidence; 2) reconstruct flood drainage routes, landscape impact, hydrology, and relative chronology; and 3) hypothesize scenarios of ice margin position and glacial lake evolution. Interpreting flood landform assemblages reveals a more extensive geomorphologic record than previously reported, with a complex drainage pattern along four separate routes from two potentially different sources. Reconstructed peak flow discharges span four orders of magnitude from 10² to 10$^5$ m³/s. Geomorphologic and paleohydraulic results introduce four hypothesized drainage scenarios, though absolute geochronology is necessary to determine whether multiple floods drained along each route. The Hvítá jökulhlaups yield insight into the timing and dynamics of the final phase of Icelandic Ice Sheet decay, advancing understanding of Iceland’s Pleistocene–Holocene transition, demonstrating the importance of high magnitude, low frequency floods in landscape evolution, and serving as an analogue to ice and meltwater response to past, present, and future climate warming in glaciated regions worldwide.

Arctic regions are warming at more than double the global average rate with significant impacts on glaciers and hydrologic systems. Iceland is on the front line of this rapid climate change, with a predicted loss of ~20% of its current ice cap volume by 2100. Much of this meltwater is stored in proglacial lakes at outlet glaciers, which are at risk of draining in glacial lake outburst floods (GLOFs). Most contemporary outburst floods in Iceland have been triggered by subglacial eruptions and geothermal activity; however, GLOFs resulting from mass movement events into lakes are an emerging—yet understudied—hazard. Many of Iceland’s proglacial lakes form in overdeepened basins, storing large volumes of meltwater; expanding lake extent creates more surface area for mass movements to enter; and retreating glaciers remove support from valley walls, increasing rockfall and landslide risk. Several large rockfalls have fallen onto glaciers in the past decades; however, these events may enter lakes as glacier retreat progresses and lakes expand.We investigate this emerging hazard by predicting proglacial lake evolution and assessing GLOF risk under a future warming climate at three sites in south Iceland. This presentation focuses on the proglacial lake at Fjallsjökull, an outlet glacier of the Vatnajökull ice cap. We present lake volume changes since 1980, derived from bathymetric surveys and mapped lake surface areas. We then estimate future lake volume and extent changes from the present until 2100 based on: 1) local topography derived from bathymetric mapping, ArcticDEM, and subglacial topography from radio-echo sounding surveys; and 2) projected glacier retreat under different climate warming scenarios. Next, we identify potential hazards from mass movement events entering the lake at its current and future extents based on field mapping and remote sensing imagery. Finally, we discuss implications of a glacial outburst flood on downstream communities, infrastructure, and tourism, laying the foundation for future work on hazard assessment and flood modeling. This site is an excellent pilot study for this emerging hazard in Iceland and has significant potential for application to other Icelandic and Arctic glacial lakes.

In many regions of the Northern Hemisphere, permafrost is thawing due to climate change. In steep terrain, this permafrost degradation can affect slope stability. In one of Iceland's eastern fjords, Seyðisfjörður, nine major landslide cycles have occurred in the last century, originating from the lower parts (< 500 m a.s.l.) of the Strandartindur slopes, with the largest landslide event ever recorded in Iceland occurring in December 2020. Its triggering mechanism is being intensively studied and its development is being monitored. In addition to these instabilities, slow movements are also observed in the upper part (> 500 - 1010 m a.s.l.) of these slopes. In these upper areas, it is not known whether permafrost is present in the subsurface or what is causing it to creep downward. To further investigate the stability of these slopes, it is important to know and map the distribution and condition of possible permafrost layers. Therefore, electrical resistivity tomography (ERT) and ground penetrating radar (GPR) measurements were performed to study the presence and distribution of permafrost in the mountain, Strandartindur, above Seyðisfjörður. A combination of measurements is used as ERT responds primarily to the electrical resistivity of the subsurface, but this can depend strongly on other factors such as porosity, water content, etc., and GPR can help map the presence of different interfaces in the soil determined by their different physical properties, such as relative electrical permittivity, but also conductivity, which is the reciprocal of resistivity. Combining the two methods allows us to get a clearer picture of the subsurface. As a benchmark for ERT measurements in the field, a laboratory setup was performed with soil and rock samples at different temperatures and water saturations to study the behavior of frozen and non-frozen conditions in our geologic environment. With all of these measurements, we aim to answer the questions of whether permafrost is present in the selected area, what the distribution of permafrost is, whether we can use laboratory ERT to establish reference resistivity values, and if these methods are appropriate for this area.

In 1968 the Siglufjarðarvegur road was built in north Iceland, serving as the only whole year road connecting the remote town of Siglufjörður with the capital city of Reykjavík. This road cuts through the area of Almenningar where three active slow moving landslides are situated, these are the Tjarnadalir, Þúfnavellir and Hraun landslides. The constant activity of these landslides affect a 5-6 km long stretch of the road that has been a problem both for the road authorities as well as travellers in terms of safety and maintenance. All three landslides have been mapped and studied before and the northernmost area of Tjarnadalir has gained the most attention as rate of movement is considered to be up to 1 m/yr for some periods. This is also the case for the southernmost Hraun landslide (0.83 m/yr) but the Þúfnavellir landslide in the middle is moving much slower with an estimated rate of 0.17 m/yr. The movement rate is constant with shorter periods of increased activity and there is strong evidence that the rate of movement is directly linked with weather patterns as more water in the landslide systems seems to cause increased activity. Ever since the year 1977, the road authorities have conducted GPS displacement measurements on a yearly basis with a limited number of points that are all situated along the road. Little is known about the different movement rates within the landslide bodies themselves but this study extends these displacement measurements through the application of remote sensing. Aerial photogrammetry comparison will be conducted with the feature tracking method in order to estimate the rate of movement throughout the entirity of all three landslide bodies. Available data extends back to the year 1954 to present day, giving an unprecedented insight into the temporal and spatial dynamics of the landslides.

One of the most visible consequences of climate changes in Iceland are retreating outlet glaciers and formation of proglacial lakes. It is estimated that Icelandic glaciers have lost about 16% of their mass since 1890 or over a 130-year time interval. Temperatures have been fluctuating over this period with exceptional warm period in the 1920s and 1930s followed by slightly colder interval until beginning of the 1980s. During this time outlet glacier retreated considerably but around 1970 glaciers begun to readvancing which continued until around 1995. At the end of the 20th century another turning point occurred, with higher temperatures and rapidly retreating outlet glaciers. Existing proglacial lakes expanded and many new were formed in front of the rapidly retreating ice margins. Over the last years temperature have become more stable and several outlet glaciers have been showing a readvancing phase. Glacial fluctuations have affected the stability of valley slopes above retreating outlet glaciers and their proglacial lakes. Resulting in increased frequency of mass movements and slope deformation in these high-mountain regions. In 1967 a large rockslide fell onto the Steinsholtsjökull outlet glacier and into its proglacial lake causing a GLOF.The rockslide was approximately 20 million m3 in volume. The head scarp was around 970 m long and up to 300 m high. It fell onto the western side of the glacier and broke up its snout. Part of the rockslide material fell into a proglacial lake, in front of the ice margin, causing a large GLOF down the valley. Large amounts of sediment were transported and redistributed down-valley with the GLOF. About 20km downstream a maximum flood discharge of 2100-2700 m3/s, was estimated.The Steinsholtsjökull 1967 GLOF, entirely overprinted the proglacial landscape in the Steinsholtsdalur valley. Similar circumstances to the valley prior to the event, now exist and are forming in glacial environments around Iceland’s present-day outlet glaciers, which highlights the urgent need to study and monitor these environments.

Since the end of the Little Ice Age in the late 19th century Iceland’s glaciers have experienced dramatic mass loss. Thinning outlet glaciers are exposing oversteepened rock slopes, which sometimes adjust in the form of slow slope deformations that can occasionally result in catastrophic paraglacial rock slope failures. Especially around the country’s deglaciating central volcanoes large landslides have occurred in the past decades. We describe a cluster of gravitational mass movements around the margin of the Svínafellsjökull outlet glacier in Southeast Iceland. The glacier margin is a popular tourist attraction with hundreds of visitors daily. Housing, a hotel, a gas station and the national ring-road are located within one kilometer downstream from the glacier. The largest deformation in the valley is located on the northern slope of Mt. Svínafellsfjall and is evidenced by a 2-km-long fracture system that separates an area of about 1km2 and a rock volume in the range of 50-150x106m3 from the mountain slope. The unstable slope is characterized by about elongated 200 sinkholes where soil cover has collapsed into underlying bedrock fractures. In several places across the slope, deep vertical bedrock fractures with no visible vertical displacement were observed. Based on morphological and structural mapping we suggest that the deformation occurs as a composite slide. Remote sensing data, eyewitnesses and field observations indicate that the onset of the deformation occurred between 2003 and 2007. This is parallel with the fastest glacier thinning rate within the 131-year record of existing data. Since 2011 the glacier surface hasn’t lowered significantly, in part due to the deposits of a large debris avalanche from 2013 on the glacial tongue which protect the glacier against ablation. The slope hasn’t shown new signs of deformation since 2018. It is however likely that the slope deformation will start again when glacier thinning continues. Even though deformation rates have been small it is crucial to continue monitoring the slope since several large rock slope failures in Iceland have shown only a short pre-failure deformation period. In a worst-case scenario a catastrophic landslide could travel across the glacier and enter two pro-glacial lakes which may lead to an outburst flood. This study shows how climate change driven glacier thinning has and likely will have further destabilizing effects on paraglacial slopes in Iceland and similar environments elsewhere.

Following last deglaciation, glacially eroded hillslopes of the Tröllaskagi peninsula in N-Iceland experienced intensive rockslide activity. In the Almenningar site, located on the outermost part of the peninsula, several rockslide features show active surface displacement, which have repeatedly caused major damages and hazardous conditions to a road crossing the area. Since 1977 the Icelandic Road and Coastal Administration (IRCA) has maintained regular measurements and in 2022, GNSS stations were installed for real time monitoring. These measurements indicate deformation rates up to 70 cm per year. Monitoring results further suggest a relationship between deformation and hydroclimatological factors. Furthermore, the front of the deformation area reaches the coast forming up to 60 m high cliffs where clear indications of extensive coastal erosion can be found. Whereas traditional landslide monitoring and field measurements can be expensive and time consuming, remote sensing methods such as Differential satellite Interferometric Synthetic Aperture Radar (D-InSAR) time series analysis has proven to be a valuable tool for large-scale slope deformation detection. In our study, we implement multitemporal D-InSAR methods, which decrease limiting factors like atmospheric delay, orbital errors and decorrelation. We use the Copernicus Sentinel-1 SAR satellite constellation with its 6 day (since 2022: 12 day) revisit time over Iceland. Besides the monitored Almenningar site, two additional sites in Tröllaskagi, Stífla and Siglufjarðarfjall, were selected for slope deformation detection due to their landform similarity and possible threat to infrastructure. The displacement time series was generated for the summers of 2016 through 2022 to (i) detect the spatio-temporal slope deformation patterns in Almenningar, Stífla and Siglufjarðarfjall, (ii) analyse if these landforms have similar deformation response to hydroclimatological conditions and/or seismic episodes and (iii) if there is noticeable difference in deformation rates at the coast or inland. The results of this research will be presented here. In conclusion, D-DInSAR provides useful information to analyse other rockslide features in Tröllaskagi and correlate detected deformation to hydroclimatological conditions and seismic episodes. Results will serve as an important support for hazard and risk assessment and contribute to further research on triggering factors.

International audience; The massive worldwide deglaciation leads to more frequent slope instabilities in mountainous terrains. The physical processes leading to such destabilizations are poorly constrained due to little monitoring of dynamic parameters at the local scale. Here we study a very large slow-moving landslide (∼0.8 km2), on the flank of Tungnakvíslarjökull glacier in Iceland. Based on a combination of remote sensing images, we monitor the landslide and glacier kinematics over 75 years, with a focus over the period 1999-2019 when rapid glacier wastage has been observed. The landslide accelerates from 2 to 45 m/yr in the 6 years following a sudden increase in glacier mass loss. This acceleration coincides with intense quake activity (Mℓ < 2.8), recorded by a regional seismic network. We show that this seismicity is caused by the landslide sliding on a rough surface. The evolution of the quake magnitudes suggests a progressive segmentation of the landslide mass during its acceleration.

International audience; Mass-movements in cold and Polar climates often involve permafrost and ice and hence these two phenomena are recurring themes throughout this chapter. We consider specifically mass movements in glacial, periglacial and paraglacial settings. For each environmental setting we describe the types of mass movement that have been documented in the literature, describing the current research foci and remaining challenges. We specifically highlight that mass-movements in cold and Polar climates are particularly sensitive to climate change, because of the involvement of permafrost and ice in their triggering and dynamics and therefore we may anticipate an increasing frequency and increased hazard from these phenomena in the future in response to unprecedented rates of environmental change.

Many ice-marginal lakes have formed in front of glacier termini in Iceland in recent decades due to climate warming, particularly at the southern margin of Vatnajökull ice cap where several such lakes grow year-by-year at present. At the same time, most glacier-dammed lakes at the lateral ice margins have shrunk or disappeared because of glacier thinning, and jökulhlaups released from them have become smaller. This paper describes changes in glacial lakes in SE-Iceland, from Skeiðarárjökull west of Öræfi to Hoffellsjökull in Hornafjörður. Lakes started to form in front of several glaciers in this area in the 1930s but most did not grow much until the 1990s, except for Jökulsárlón by Breiðamerkurjökull, which has grown steadily since before the middle of the last century. Currently, there are growing terminus lakes by all the main south-flowing outlet glaciers of Vatnajökull, with a combined area of ~60 km². The subglacial landscape upstream of the termini indicates that the lakes will continue to grow in the coming decades as a consequence of glacier downwasting if the climate warms as projected. These lakes affect the ice flow and the mass and energy balance of the respective glaciers because of their effect on the force balance of the terminus region, the calving of ice into the lakes, and the absorption of heat spent for melting of calved ice fragments and the terminus ice front. The lakes can cause hazard to settlements and travellers in the adjacent area, as landslides on the glaciers that propagate into the lakes can create tsunami waves with a high run-up and sudden, very dangerous flash floods in the glacier forelands.

International audience; The aim of this work is to study the process of transformation of debris-free mountain glaciers into debris-covered glaciers and rock glaciers, and to examine the factors driving diverging evolution in similar glacial systems. The study area is the Hofsdalur valley, in the Trollaskagi peninsula (northern Iceland), where several cirques host a great diversity of glaciers and rock glaciers as well as various glacial landforms. Four adjacent cirques have been analysed through a multidisciplinary approach: geomorphological analysis, boulder surface displacement tracking, quantification of recent glacier changes, three dimensional palaeoglacier reconstruction, equilibrium-line altitude calculations and relative and direct dating methods applied to surface boulders. Dating methods included in situ Cl-36 cosmic-ray exposure dating, Schmidt hammer weathering measurements and lichenometric dating. The results confirm that glaciers in Hofsdalur followed an evolution pattern similar to that observed in other cirques in the Trollaskagi peninsula. During the Younger Dryas (12.9-11.7 ka) many of those cirques hosted debris-free glaciers, whose retreat started in the early Holocene. Distinct retreat dynamics and cirque floor elevation conditioned the subsequent glacial evolution. In some Trollaskagi cirques, the ice completely covered the headwalls, which consequently did not supply debris onto the glacier surface, which remained debris-free. In most of these cirques, however, glacier retreat enhanced paraglacial processes and the ice-free cirque walls generated a high debris supply onto the glacier surface. As a result, the glaciers evolved towards debris-covered glaciers or rock glaciers, depending on the local topographical setting. In the lower cirques they collapsed immediately after their formation. At higher altitudes, above the lower permafrost limit, these ice-cored landforms have survived until the present day, but they have been stagnant since the Holocene Thermal Maximum, while the heads of these cirques have hosted debris-free glaciers during the Late Holocene.

A.S.T.E.R. TEAM : Georges Aumaître, Didier Bourlès et Karim Keddadouche; International audience; The objective of this work is to chronologically establish the origin of the different glacial and rock glacier complex landforms deposited by Heoinsdalsjokull glacier (65 degrees 39' N, 18 degrees 55' W), in the Heoinsdalur valley (Skagafjorour fjord, Trollaskagi peninsula, central northern Iceland). Multiple methods were applied: geomorphological analysis and mapping, glacier reconstruction and equilibrium-line altitude calculation, Cosmic-Ray Exposure dating (in situ cosmogenic Cl-36), and lichenometric dating. The results reveal that a debris-free glacier receded around 6.6 +/- 0.6 ka, during the Holocene Thermal Maximum. The retreat of the glacier exposed its headwall and accelerated paraglacial dynamics. As a result, the glacier terminus evolved into a debris-covered glacier and a rock glacier at a slightly higher elevation. The front of this rock glacier stabilized shortly after it formed, although nuclide inheritance is possible, but its sector close the valley head stabilized between 1.5 and 0.6 ka. The lowest part of the debris-covered glacier (between 600 and 820 m altitude) collapsed at ca. 2.4 ka. Since then, periods of glacial advance and retreat have alternated, particularly during the Little Ice Age. The maximum advance during this phase occurred in the 15th to 17th centuries with subsequent re-advances, namely at the beginning of the 19th and 20th centuries. After a significant retreat during the first decades of the 20th century, the glacier advanced in the 1960s to 1990s, and then retreated again, in accordance with the local climatic evolution. The internal ice of both the debris-covered and the rock glacier have survived until the present day, although enhanced subsidence provides evidence of their gradual degradation. A new rock glacier developed from an ice-cored moraine from around 1940-1950 CE. Thus, the Holocene coupling between paraglacial and climatic shifts has resulted in a complex evolution of Heoinsdalsjokull, which is conflicting with previously proposed models: a glacier, which had first evolved into a debris-covered and rock glacier, could later be transformed into a debris-free glacier, with a higher sensitivity to climatic variability.

Publisher's version (útgefin grein), Molards have been defined in the past as conical mounds of debris that can form part of a landslide's deposits. We present the first conclusive evidence that molards in permafrost terrains are cones of loose debris that result from thawing of frozen blocks of ice-rich sediments mobilised by a landslide, and hence propose a rigorous definition of this landform in permafrost environments. We show that molards can be used as an indicator of permafrost degradation, and that their morphometry and spatial distribution give valuable insights into landslide dynamics in permafrost environments. We demonstrate that molards are readily recognisable not only in the field, but also in remote sensing data; surveys of historic aerial imagery allow the recognition of relict molards, which can be used as an indicator of current and past permafrost conditions. The triggering of landslides as a result of permafrost degradation will arguably occur more often as global atmospheric temperatures increase, so molards should be added to our armoury for tracking climate change, as well as helping us to understand landslide-related hazards. Finally, we have also identified candidate molards on Mars, so molards can inform about landscape evolution on Earth and other planetary bodies., This work has been funded by a postgraduate studentship grant (NE/L002493/1) from the Central England Natural Environment Research Council Training Alliance (CENTA). This project forms part of and is funded by a British Geological Survey BUFI CASE Studentship (GA/14S/024, Ref: 284). We thank the Natural Environment Research Council Airborne Research Facility (NERC ARF) and their Data Analysis Node (NERC-ARF-DAN) plus the EUropean Facility for Airborne Research (EUFAR) for the air photography and LiDAR data on which this paper relies. Thanks go to NERC Geophysical Equipment Facility (GEF) for the Loans 1048 and 1064 through which differential GPS surveys were possible. We thank the GeoPlanet writing residential scheme for the support in writing this manuscript. C. Jordan publishes with permission of the Executive Director of BGS. S. J. Conway is funded by the French Space Agency, CNES, for her HiRISE related work. We gratefully acknowledge the contribution of Gestur Hansson (Icelandic Meteorological Office) and of our field assistants Francesco Giuntoli, Silvia Crosetto, and Sydney Gunnarson. The authors thank the reviewers Anja Dufresne, Marten Geertsema and Gioachino Roberti for their insightful comments.

This paper analyses changes in the surface morphology of rock and debris-covered glaciers in the Holadalsjokull and Fremri-Grjotardalur cirques near Holar village in the Trollaskagi peninsula (northern Iceland) (65°43′55″N; 19°06′49″W, 160 m), to understand the dynamics and climatic significance of these landforms. The study includes an analysis of historical aerial photographs from 1946 to 2000. The aim was to evaluate surface changes in these landforms and obtain the horizontal displacement and elevation changes of large boulders and linear features (ridges and furrows) at each date. In addition, the surface elevation differences between 1980 and 1994 were obtained from digital elevation models. The horizontal displacement results obtain a mean velocity of 0.33 m yr−1 and an average elevation difference of −0.72 m for the boulders, with the linear features advancing 14.84 m during the period 1946–2000. Except for this slow mobility, no changes occurred in the surface morphology of these landforms during the 54 years. The low displacement rates of boulders and linear features, together with the surface lowering processes observed in these landforms, indicate that widespread melting is the most important activity in the debris-covered and rock glaciers in Trollaskagi. This is confirmed by the recent formation of collapse depressions.

Resilience to natural hazards depends on a person's ability to envision an event and its consequences. While real life experience is precious, a real event experience is rare, and sometimes fatal. So, virtual reality provides a way to getting that experience more frequently and without the inconvenience of demise. Virtual reality can also enhance an event to make it more visible, as often things happen in bad weather, at night or in other inconvenient moments.The 3DTeLC software (an output from an ERASMUS+ project, http://3dtelc.lmv.uca.fr/) can handle high-resolution 3D topographic models and the user can study natural hazard phenomena with geological tools in virtual reality. Topography acquired from drone or plane acquisitions, can be made more accessible to researchers, public and stakeholders. In the virtual environment a person can interact with the scene from the first person, drone or plane point of view and can do geological interpretation at different visualization scales. Immersive and interactive visualization is an efficient communication tool (e.g. Tibaldi et al 2019 – Bulletin of Volcanology DOI: https://dx.doi.org/10.1007/s00445-020-01376-6).We have taken the 3DTeLC workflow and integrated a 2.5D flow simulation programme (VOLCFLOW-C). The dynamic outputs from VOLCFLOW-C are superimposed into a single visualization using a new tool developed from scratch, which we call VRVOLC. This coupled visualization adds dynamic and realistic understanding of events like lahars, lava flows, landslides and pyroclastic flows. We present two examples of this, one developed on the Digital Terrain Model of Chachani Volcano, Arequipa Peru, to assist with flood and lahar visualisation (in conjunction with INGEMMET, UNESCO IGCP project 692 Geoheritage for Resilience and Cap 20-25 Clermont Risk). And another with an Icelandic debris slide that occurred in late 2014 possibly related to permafrost degradation (in conjunction with the ANR PERMOLARDS project).We thank out 3DTeCL colleagues, without which this would not be possible, and acknowledge financial support for the PERMOLARDS project from French National Research Agency (ANR-19-CE01-0010), and this is part of UNESCO IGCP 692 Geoheritage for Resilience.

As consequence of ongoing climate change, permafrost degradation is thought to be increasingly affecting slope stability in periglacial environments. This is of growing concern in Iceland, where in the last decade, permafrost degradation has been identified among the triggering factors of landslides. The role of ground ice in conditioning the morphology and dynamics of landslides involving loose deposits is poorly understood. We show the geomorphological impact of the Móafellshyrna and Árnesfjall landslides that recently occurred in ice-cemented talus deposits in northern Iceland. Using field and aerial remote-sensing measurements of the morphological and morphometric characteristics of the landslides, we assess the influence of thawing ground ice on their propagation style and dynamics. The two mass movements are complex and are similar to rock- and debris-ice avalanches, changing trajectory and exhibiting evidence of transitioning their style of motion from a dry granular mass to a debris flow-like movement via multiple pulses. We infer that the thawing of ground ice together with the entrainment of saturated material provided the extra fluid causing this change in dynamics. The hazardous consequences of permafrost degradation will increasingly affect mountain regions in the future, and ground-ice thaw in steep terrain is a particularly hazardous phenomenon, as it may induce unexpected long-runout failures and can cause slope instability to continue even after the landslide event. Our study expands our knowledge of how landslides develop in unstable ice-cemented deposits and will aid assessment and mitigation of the hazard that they pose in Iceland and other mountainous periglacial areas.

The Saint-Venant equations are usually the basis of numerical models for landslide flows. They are nonstationary and nonlinear. The theory for translatory waves in a prismatic channel and a funneling channel can be used for landslides using the assumption of either turbulent or laminar flow in the slide. The mathematics of translatory waves traveling over dry land or superimposed on another flow are developed. This results in a new slope factor controlling the flow velocity, together with the Chezy coefficient used in previous applications of the translatory wave theory. Flow times for the slide to reach a given destination, slide depth, and velocity can be calculated using the initial magnitude of the flow in the slide. The instabilities of the wave tail are discussed. Three case studies are presented: a submarine slide that started the Tohoku tsunami in Japan, the Morsárjökull rock avalanche in SE Iceland, and the Móafellshyrna slide in central N Iceland.

Landslide mapping and analysis are essential aspects of hazard and risk analysis. Landslides can block rivers and create landslide-dammed lakes, which pose a significant risk for downstream areas. In this research, we used an object-based image analysis approach to map geomorphological features and related changes and assess the applicability of Sentinel-1 data for the fast creation of post-event digital elevation models (DEMs) for landslide volume estimation. We investigated the H&iacute, tardalur landslide, which occurred on the 7 July 2018 in western Iceland, along with the geomorphological changes induced by this landslide, using optical and synthetic aperture radar data from Sentinel-2 and Sentinel-1. The results show that there were no considerable changes in the landslide area between 2018 and 2019. However, the landslide-dammed lake area shrunk between 2018 and 2019. Moreover, the H&iacute, tar&aacute, river diverted its course as a result of the landslide. The DEMs, generated by ascending and descending flight directions and three orbits, and the subsequent volume estimation revealed that&mdash, without further post-processing&mdash, the results need to be interpreted with care since several factors influence the DEM generation from Sentinel-1 imagery.

International audience; Eighteen samples for 36Cl Cosmic-Ray Exposure (CRE) dating were taken from glacially polished bedrocks, mo- raine boulders, fossil/active rock glaciers and debris-covered glaciers in Fremri-Grjótárdalur and Hóladalur cirques in the Víðinesdalur, Hofsdalur and Héðinsdalur valleys, close to Hólar village, in the Tröllaskagi peninsula, northern Iceland. Boulder sampling was preceded by a study of the boulder stability with the twofold aim of: en- suring that the surfaces to be sampled were stable enough for the reliable application of CRE dating, and to better understand the relation between the glacier dynamics and exposition history. The results show that the glaciers which occupy the valleys in Tröllaskagi began their retreat around 16 ka. Later, the glaciers advanced again around 11 ka within the cirques, and small moraines were formed. Thereafter, these small glaciers retreated and evolved into rock glaciers as debris from paraglacial processes accumulated on the glacier surface. The fronts of these rock glaciers stabilized definitively shortly after their formation and became eventually fossil after the melting of their internal ice. New rock glaciers and debris-covered glaciers formed afterwards, which still have internal ice at present, although their current dynamics are mostly related to subsidence. The stabilization of these rock glaciers and debris-covered glaciers is dated to the period between 7 and 3 ka, although they may have been reactivated during cold neoglacial periods. This research demonstrates the potential interest in apply- ing CRE dating methods to debris-covered glaciers and rock glaciers to determine their origin, evolution and phase of cessation of internal movement until they finally lost their internal ice and became fossil.

Glacial lake outburst floods (GLOFs) have occurred across the planet throughout the Quaternary and are a significant geohazard in Arctic and alpine regions today. Iceland experiences more frequent GLOFs—known in Icelandic as jökulhlaups—than nearly anywhere on Earth, yet most research focuses on floods triggered by subglacial volcanic and geothermal activity. However, floods from proglacial lakes may be a better analogue to most global GLOFs.As the Icelandic Ice Sheet retreated across Iceland in the Late Pleistocene-Early Holocene, meltwater pooled at ice margins and periodically drained in jökulhlaups. Some of the most catastrophic floods drained from ice-dammed Glacial Lake Kjölur, surging across southwestern Iceland from the interior highlands to the Atlantic Ocean. These floods left extensive geomorphologic evidence along the modern-day course of the Hvítá River, including canyons, scoured bedrock, boulder deposits, and Gullfoss—Iceland’s most famous waterfall. The largest events reached an estimated maximum peak discharge of 300,000 m3 s-1, ranking them among the largest known floods in Iceland and on Earth.Yet, all our evidence for the Kjölur jökulhlaups comes from only one publication to date (Tómasson, 1993). My research employs new methods to better constrain flood timing, routing, magnitude, and recurrence interval at this underexplored site. This talk presents new and synthesized jökulhlaup geomorphologic evidence; HEC-RAS hydraulic modeling results of flow magnitude and routing; and ongoing geochronological analyses using cosmogenic nuclide exposure dating and tephrochronology. It also situates these events within Icelandic Ice Sheet deglaciation chronology and environmental change at the Pleistocene-Holocene transition. Finally, it examines the Kjölur floods as an analogue to contemporary ice sheet response, proglacial lake formation, and jökulhlaup processes and landscape evolution in Arctic and alpine regions worldwide, where GLOFs pose an increasing risk to downstream communities due to climate-driven meltwater lake expansion. Citation: Tómasson, H., 1993. Jökulstífluð vötn á Kili og hamfarahlaup í Hvítá í Árnessýslu. Náttúrufræðingurinn 62, 77-98.

A large slow rock mass deformation has been detected in a mountain side north of the Tungnakvíslarjökull outlet glacier, located in the western part of the Mýrdalsjökull glacier in Iceland. A group of scientist from the University of Iceland, National Land Survey and Icelandic GeoSurvey have worked on collecting data from several sources and installed monitoring equipment at the site. According to observations, which were based on comparison of DEM from aerial photographs from 1945 to 2019, the slope has been showing slow rock mass deformation since at least 1945. The rate of movements has been estimated for the period from 1945 to 2019. The data show that the total displacement since 1945 is around 200 m. The data also indicate that the deformation rate has not been constant over this time period and the data shows that the maximum deformation was between 1999 and 2004 of total of 94 m or about 19 m/year.The mountain slope north of the Tungnakvíslarjökull outlet glaciers reaches up to around 1100 m height. The head scarp of the slide, which is almost vertical, is around 2 km wide rising from about 4-500 m in the western part up to the Mýrdalsjökull glacier at 1100 m in the east. The total sliding from the head scarp down to the present day ice margin is around 1 km2. The total volume of the moving mass is not known as the sliding plane is not known, but the minimum volume might be between 100 to 200 million m3. The entire slope shows signs of displacement and is heavily fractured and broken up. A GPS station that was installed in the uppermost part of the slope in August shows that the slope is moving about 3-9 mm per day, at a constant rate since installation.There are two main ideas of the causes for this slow rock mass deformation. One is the consequences of slope steepening by glacial erosion, followed by unloading and de-buttressing due to glacial retreat. Another proposed cause for the deformation is related to its location on the western flank of the Katla volcano. Persistent seismic activity in this area for decades may be explained by a slowly rising cryptodome, which may also explain the slope failure.

Debris flows are fast‐moving gravity flows of poorly sorted rock and soil, mixed and saturated with water. Debris‐flow initiation has been studied using empirical and experimental modelling, but the geomorphic changes, indicative of different triggering processes, are difficult to constrain with field observations only. We identify signatures to distinguish two different debris‐flow release styles by integrating high‐resolution multi‐temporal remote sensing datasets and morphometric analysis. We analyse debris flows sourced above the town of Isafjorður (Iceland). Two debris‐flow triggering processes were previously hypothesized for this site: (i) slope failure, characterised by landslides evolving into debris flows, and (ii) the fire‐hose effect, in which debris accumulated in pre‐existing, steep‐sided bedrock passages is transported by a surge of water. It is unknown which process dominates and determines the local risk. To investigate this question, we compare airborne LiDAR elevation models and aerial photographs collected in 2007 with similar data from 2013. We find that two new debris‐flow tracks were created by slope failures. These are characterised by steep sliding surfaces and lateral leveed channels. Slope failure also occurred in two large, recently active tracks, creating the preparatory conditions for the fire‐hose effect to mobilise existing debris. These tracks show alternating zones of fill and scour along their length, and debris stored below the source‐area at rest angles >35°. Our approach allows us to identify and quantify the morphological changes produced by slope failure release process, which generated the preparatory conditions for the fire‐hose effect. As debris flows are rarely observed in action and morphological changes induced by them are difficult to detect and monitor, the same approach could be applied to other landscapes to understand debris‐flow initiation in absence of other monitoring information, and can improve the identification of zones at risk in inhabited areas near hillslopes with potential for debris flows.

The Tröllaskagi peninsula is located in northern Iceland, between meridian 19°30′W and 18°10′W, jutting out into the North Atlantic to latitude 66°12′N. The aim of this research is to study recent glacier changes in relation to climatic evolution of the Gljúfurárjökull and Tungnahryggsjökull debris-free valley glaciers in Tröllaskagi. Glacier extent mapping and spatial analysis operations were performed with ArcGIS (ESRI), using analysis of aerial photographs from 1946, 1985, 1994 and 2000, and a 2005 SPOT satellite image. The results show that these glaciers lost a quarter of their surface area between the ‘Little Ice Age’ and 2005. In this paper, the term ‘Little Ice Age’ follows Grove (2001) as the most recent period when glaciers extended globally between the medieval period and the early 20th century. The abrupt climatic transition of the early 20th century and the 25-year warm period 1925–1950 triggered the main retreat and volume loss of these glaciers since the end of the ‘Little Ice Age’. Meanwhile, cooling during the 1960s, 1970s and 1980s altered the trend, with advances of the glacier snouts. Between the ‘Little Ice Age’ and the present day, the mean annual air temperature and mean ablation season air temperature increased by 1.9°C and 1.5°C, respectively, leading to a 40–50 m rise in the equilibrium line altitude (ELA) of the glaciers during this period. The response of these glaciers depends not only on the mean ablation season air temperature evolution but also on other factors such as winter precipitation. The models applied show a precipitation increase of up to more than 700 mm since the ‘Little Ice Age’.

International audience; The Tröllaskagi Peninsula in northern Iceland hosts more than a hundred small glaciers that have left a rich terrestrial record of Holocene climatic fluctuations in their forelands. Traditionally, it has been assumed that most of the Tröllaskagi glaciers reached their Late Holocene maximum extent during the Little Ice Age (LIA). However, there is evidence of slightly more advanced pre-LIA positions. LIA moraines from Iceland have been primary dated mostly through lichenometric dating, but the limitations of this technique do not allow dating of glacial advances prior to the 18th or 19th centuries. The application of 36Cl Cosmic-Ray Exposure (CRE) dating to Tungnahryggsjökull moraine sequences in Vesturdalur and Austurdalur (central Tröllaskagi) has revealed a number of pre-LIA glacial advances at ~400 and ~700 CE, and a number of LIA advances in the 15th and 17th centuries, the earliest LIA advances dated so far in Tröllaskagi. This technique hence shows that the LIA chronology in Tröllaskagi agrees with that of other European areas such as the Alps or the Mediterranean mountains. The combined use of lichenometric dating, aerial photographs, satellite images and fieldwork shows that the regional colonization lag of the commonly used lichen species Rhizocarpon geographicum is longer than previously assumed. For exploratory purposes, an alternative lichen species (Porpidia soredizodes) has been tested for lichenometric dating, estimating a tentative growth rate of 0.737 mm yr−1.

In 2014, the Varnes classification system for landslides was updated. Complex landslides can still be a problem to classify as the classification does not include the flow type in the hydrodynamical sense. Three examples of Icelandic landslides are presented and later used as case studies in order to demonstrate the methods suggested to analyze the flow. The methods are based on the different physical properties of the flow types of the slides. Three different flow types are presented, named type (i), (ii), and (iii). Types (i) and (ii) do not include turbulent flows and their flow paths are sometimes independent of the velocity. Type (iii) include high velocity flows, they are treated with the translator wave theory, where a new type of a slope factor is used. It allows the slide to stop when the slope has flattened out to the value that corresponds to the stable slope property of the flowing material. The type studies are for a fast slide of this type, also a large slip circle slide that turns into a fast-flowing slide farther down the path and finally a large slide running so fast that it can run for a kilometer on flat land where it stops with a steep front.

Real-time monitoring of volcanic eruptions in Iceland, using satellite remote sensing, has expanded during the last decade. Availability of satellite images has increased extensively in the last few years, with improved geometric, radiometric, and time resolution, in addition to shortened delivery time. This paper provides an overview and a brief historical perspective of the topic.

International audience; For several decades, geomorphologists have focused on the functioning of geomorphic systems after deglaciation. The relative importance of paraglacial vs. periglacial processes has been highly debated. At present, the development of dating techniques allows to contribute to this debate. We reconstruct in this paper the geomorphic evolution of Tindastóll mountain slopes in Laxárdalur valley (Skagafjörður area, central northern Iceland), where a chronological framework can be established through tephrochronology and an assemblage of dated raised beaches. Volumetric calculations of constructed and excavated landforms were created from field data and from DEM and geographical information system techniques. Collectively, our data exhibit a first stage of paraglacial landsliding during the first half of the Holocene, followed by a stage of scree and rockglacier development (during the second half of the Holocene, but before 1100 AD). Our estimations indicate that more than 85% of the total sediment production were due to rock slope failure, and the rate of bedrock denudation due to periglacial processes was about one half of the rate of paraglacial processes. Nevertheless, paraglacial and periglacial processes cannot be seen here as antagonistic processes: they are organized in a sequence during which periglacial processes are conditioned (enhancement of bedrock denudation rates) by fracturing and consequent mass wasting. Screes and concomitant rockglaciers were indeed preconditioned by the landslide, while areas non-affected by landslides have remained mostly intact, characterized by a very low rate of accumulation due to geomorphic (periglacial) activity.

International audience; In Iceland there are numerous rock-slope failures, especially in the Tertiary basaltic formations of the northern, eastern and northwestern regions. The temporal pattern of rock-slope failures is fundamental for understanding post-glacial events. In the Skagafjörður district, central northern Iceland, 17 rock-slope failures were investigated to determine the age of their occurrence. A geomorphic survey was carried out to identify and characterize landform units, both on the rock-slope failures and in their immediate vicinity. In this coastal area, we used geomorphological stacking which included the relationship between rock-slope failures and raised beaches caused by glacial isostatic rebounds, the chronology of which was established in previous studies. We searched for depressions on the rock-slope failures to then excavate a series of pits and map the stratigraphy. The resulting stratigraphic framework was then validated using (i) radiocarbon dating of wood remains, and (ii) tephrochronology, both of which were complemented by age-depth model calibration. The results confirm that all the rock-slope failures potentially occurred before the Boreal (8 ka), while 94% occurred before the Preboreal (10 ka). They all potentially occurred after the glacial retreat following the maximal ice extent and the Preboreal. More precisely, 11 of them potentially occurred between the Preboreal and the first half of the Holocene. This study demonstrates the relationship between the deglaciation and destabilization of slopes during the paraglacial phase (debuttressing, decompression, glacial isostatic rebound, seismic activity, etc.), which are also controlling factors favouring landsliding, but are difficult to identify for each individual rock-slope failure.

The paper examines the potential of dendrogeomorphic analyses to deliver a one-year resolution chronology of snow-avalanche winters in Northern Iceland, at the scale of a colluvial cone covered with European White Birch trees and shrubs ( Betula pubescens Ehrh.). Reconstruction of the avalanche history is performed using tree-ring analyses. Determination of the most reliable growth disturbance (class 1 of growth eccentricity) and applying a tempering index value with threshold 10% of trees responding in the same year and at least two trees affected, avalanche-activity years are highlighted, resulting in 52 avalanche winters. Amongst those, 5 winters have activity index over 40%, indicating major years. Calculation of frequency of similar growth disturbances at each tree provides a return period ranging from 4.2 to 19 years. Inferred spatial extent of snow-avalanche events induces flow-like snow avalanches with limited extent around the tree-less parts of the cone with a return period under 6 years; the cone is totally covered and the distal tree-limit over-passed with a return period of 15–20 years.

This paper emphasizes the importance of studying diffuse rock debris accumulation in the far distal part of colluvial cones with the aim of de- fining the spatial distribution and frequency of ex- treme snow avalanches. These deposits are located at some distance from the slope and have rarely been described in the literature. The field based methods used in this study confirm the snow- avalanche origin of these deposits by (i) character- izing the distribution of the deposits along the col- luvial cones and to their furthest extent, some way from the foot of the slope, and (ii) clearly defining the orientation of the long axis of the furthest and largest boulders as parallel with the main cone axis. A relative age of the deposits is obtained by assess- ing the vegetation cover of the boulder surfaces and by measuring the rock hardness using a Schmidt hammer. The study concludes that there were fre- quent extreme snow avalanches which have oc- curred since the Little Ice Age, and that they have decreased in magnitude during the past decade.

Snow avalanches are a major hazard for many settlements and transportation corridors in northern Iceland. At many sites the occurrence of snow avalanches during the past century has not been recorded. Visible damage, such as tilting, scars and decapitation of trees and shrubs (Betula pubescens) growing on colluvial cones in a remote area in Central North Iceland clearly identifies snow-avalanche paths of a given magnitude and frequency. An analysis of tree-ring data was made using the chronology of ring sizes and wood reaction in snow-avalanche tracks subject to frequent avalanches. Abnormal growth, correlated with abrupt increases or decreases in growth rates, is related to snow-avalanche impact. The preliminary results provide reliable dendrogeomorphological data that show the spatial extent and frequency of snow avalanches in the study area. Further investigation that includes a broader sampling strategy and dendrochronological laboratory analysis is required.

This paper examines triggering factors and geomorphic significance of slush flows in the Bildudalur valley, northwestern Iceland. The area is prone to release slush flows from two confine...

Debris flows in the Gleivarhjalli area in northwestern Iceland occurred after a sudden and intensive snowmelt period during 10–12 June, 1999. The area, in the northwestern part of the town of Isafj...

Most studies focusing on landslide spatial analysis have considered the relationships between predictors and landslide occurrence as fixed effects. Yet spatially varying relationships, i.e. non-stationarity, often occur in any spatial data set and should be theoretically considered in statistical models for a better fit. In Skagafjörður, a landslide-rich north–south oriented area located in northern Iceland, we investigated whether spatial non-stationarity in the relationships between paraglacial variables (glacio-isostatic rebound and post-glacial debuttressing, both captured in this area by latitude) and landslide locations is detectable. To explore the non-stationarity of factors that predispose landslide occurrence, we performed two logistic regression models, one global (GLR) and the other enabling the regression parameters to vary locally (geographically weighted logistic regression, GWLR). Each model was computed with two types of outcome, one based on the entire masses of landslides and the other only on the scarps of landslides. GLR results reveal that increasing latitude is associated with increasing probability of landslide occurrence, confirming that post-glacial rebound is of prime importance at the regional scale. Nevertheless, GWLR indicates that this relationship is absent or reversed at some locations, meaning that the influence of paraglacial and other predisposing factors of landsliding (slope, valley depth and curvature) vary at the local scale. This result sheds light on the spatial clustering of three subzones where landsliding drivers are homogeneous. We conclude that a GWR-based approach provides some significant inputs for spatial analysis of mass movement processes, by identifying multi-scale process control zones and by highlighting local drivers, indecipherable in global models.

(2007). Sediment budgets and rates of sediment transfer across cold environments in europe: introduction and background to the european science foundation network ‘sedimentary source‐to‐sink fluxes in cold environments’(sediflux) Geografiska Annaler: Series A, Physical Geography: Vol. 89, No. 1, pp. 1-3.

The Höfðahólar rock avalanche, in the Skagafjörður area of northern Iceland, was investigated on the basis of a geomorphological analysis of its landforms and close surrounding environment. Thanks to sound chronological constraints (14C dating from birch remnants in peat areas that developed within depressions over the chaotic rock-avalanche deposit, tephrochronological sequences resulting from subsequent ash fallouts over the deposit, calibration of an age–depth model of peats and previously dated raised beaches), we define the rock-avalanche implementation with a wider timeframe between 10,200 and 7975 cal. yr BP and with a narrower frame between 9000 and 8195 ± 45 cal. yr BP. Such a well constrained timing proposes one of the most precise datings of an early-Holocene major slope failure in Iceland. This result fits well in the known chronology of the deglaciation in this area and in the prevailing Icelandic theory of a generalized phase of landsliding that occurred shortly after the deglaciation of the area. The main driver for the rock-avalanche occurrence is associated to a paraglacial origin; glacio-isostatic rebound, associated to rockwall debuttressing, is thought to be the main factor in the genesis of this Boreal major disequilibrium.

1Geological Survey of Norway (NGU), Quaternary Geology and Climate group, Trondheim, Norway 2Norwegian University of Science and Technology (NTNU), Department of Geography, Trondheim, Norway 3Queen’s University, Department of Geography, Kingston, Canada 4University of Clermont-Ferrand, Laboratory of Physical and Environmental Geography GEOLAB, CNRS, Clermont-Ferrand, France 5Natural Research Centre of North-western Iceland, Saudarkrokur, Iceland 6University of Arkansas, Department of Geosciences, Fayetteville AR, USA 7 University of Otago, Department of Geography, Dunedin, New Zealand 8University of Salzburg, Department of Geography and Geology, Salzburg, Austria 9University of Colorado, Institute of Arctic and Alpine Research, Boulder, CO, USA 10Durham University, Department of Geography, Durham, UK 11Adam Mickiewicz University, Institute of Paleogeography and Geoecology, Poznan, Poland

Active denudation processes occurring on slopes in north and northwestern Iceland have contributed to the buildup of large colluvial cones. These processes have been active since around 10,000 14C yr BP when the ice sheet retreated during the last deglaciation. Stratigraphic records provide information of the kind of sedimentary transfer processes that have been active on slopes through time. Vertical sections in colluvial cones in north and northwestern Iceland exhibit a characteristic stratigraphy with successions of material from mass-movements interbedded with soil horizons occurring throughout the Holocene, under periglacial conditions of varying intensity. The alternating organic and minerogenic units are indicators of phases of slope activity and stability. The dating of the deposits is possible with tephrochronology and 14C dating. The quantitative analysis of sediment on colluvial cones shows the relative importance of aggradation due to slope processes vs. soil formation during the Holo...

Decaulne, A., Saemundsson, °., Jonsson, H.P. and Sandberg, O., 2007: Changes in deposition on a colluvial fan during the Upper Holocene in the Tindastoll Mountain, Skagafjor√ur District, north Iceland: preliminary results. Geogr. Ann., 89 A (1): 51-63. ABSTRACT. This study investigates variability in depositional processes and landforms on the Innstaland colluvial fan, northern Iceland, over the late Holocene. This is completed using geomorpho- logical mapping, historical records and relative-age dating tools (vegetation survey, rock hardness and tephrochronology). Debris flows are the main con- tributors to fan development. Six main phases of deposition are distinguished, varying in deposit magnitude along a general trend of decreasing magnitude over time. With the help of dated tephra layers, the aggradation rates of the fan are calculat- ed for the upper Holocene and in particular over the historical period (post- AD 1104). An episodic sedi- ment transfer system is reconstructed, with several phases of low activity between more rapid aggrada- tional episodes. The interpretation of the colluvial deposits suggests that the main phase of aggrada- tion on the fan ended during the historical period af- ter which incision started (between AD 1300 and 1766). Incision tracks act as the main pathways for debris distribution at the present time. These varia- tions are related to the changing response of the catchment system over time.