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An integrated stratigraphic, sedimentological, volcanological, and geochemical studies were conducted for the first time on the eruptive products of the Marssous volcano, Bahariya Depression, Western Desert, Egypt. The rarity of complex volcanological studies in the west Red Sea rift makes these investigated volcanoes important as they offer a clue to the style of volcanism, eruptive environment and magma genesis during magmatism complimentary to those areas extensively studied in the Arabian Peninsula toward Syria and Eastern Turkey. The Marssous volcano is small monogenetic scoria cone that shows a polyphase feeding system, consisting of unconformable superimposed characteristic effusive-to-explosive eruptive units, suggesting a wide spectrum of diverse eruptive styles through a complex feeder network. On the basis of the sedimentological characteristics, field relationships, lava flow textures and granulometric indicators, five volcanic units have been identified from the base to top as (1) coherent porphyritic massive basalts (Bpm), (2) stratified tuff beds (Unit 1), (3) crude-bedded lapilli tuff beds with bombs (Unit 2), (4) massive agglutinate beds (composed of spatter and fluidal bombs) formed by lava fountains (Unit 3), (5) porphyritic vesicular basalts (Bpv), and (6) subvolcanic feeder intrusions. The degree of vesicularity and the size of the clasts increase from thin Unit 1 (ash to lapilli) through more thick Unit 2 (lapilli-bomb) to Unit 3 (breadcrusted scoriaceous bomb) as an indicative of an increased magma flux and the high eruptive energy together with an enlarged of degassing fragmentation. There is consequently a progressive evolution from an initial Phreatomagmatic explosive stage followed an initial effusive event to dry magmatic explosive (Strombolian & Hawaiian) and effusive eruptive styles in the later. With eruption progression, the external water to fuel Phreatomagmatism was diminished relatively early in the eruptions giving way to accumulate a pyorclastic fall deposition of Strombolian to Hawaiian lava-fountain episodes together with effusive eruptions, all together forming the majority of the pyroclastic and effusive successions of Gabal Marssous. These eruptive phases have happened during a continuous deposition without any time pauses in a short period of time as a result of a single cone-forming eruptions. The Marssous volcano shares resemblances in terms of inferred eruption style and structures with other scoria cones elsewhere in the broad regional context such as North Africa, Mediterranean province, and Arabian Peninsula, and thus provides an outstanding field laboratory to explore scoria cones architecture and growth from a global perspective. This volcano event is a key tectono-stratigraphic marker for an early manifestation, coinciding with the initiation of Red Sea rifting opening.

SUMMARYStudying the magnetic fabric in volcanic edifices, particularly lava flows from recent eruptions, allows us to understand the orientation distribution of the minerals related to the flow direction and properly characterize older and/or eroded flows. In this work, the magnetic fabric from recent (Quaternary) lava flows (slightly inclined in seven sites and plateau lavas in two sites), pyroclastic deposits (two sites from a scoria cone) and volcanic cones, domes and plugs (three sites) from Penguin and Bridgeman islands, located in the Bransfield backarc basin, are presented. The volcanism in the two islands is related to rifting occurring due to the opening of the Bransfield Strait, between the South Shetlands archipelago and the Antarctic Peninsula. The direction of flow of magmatic material is unknown. Rock magnetic analyses, low temperature measurements and electron microscope observations (back-scattered electron imaging and Energy Dispersive X-ray analyses) reveal a Ti-poor magnetite (and maghemite) as the main carrier of the magnetic fabric. Hematite may be present in some samples. Samples from the centre of the lavas reveal a magnetic lineation either parallel or imbricated with respect to the flow plane, whereas in the plateau lavas the magnetic lineation is contained within the subhorizontal plane except in vesicle-rich samples, where imbrication occurs. The magnetic lineation indicates a varied flow direction in Bridgeman Island with respect to the spreading Bransfield Basin axis. The flow direction in the plateau lavas on Penguin Island is deduced from the imbrication of the magnetic fabric in the more vesicular parts, suggesting a SE–NW flow. The volcanic domes are also imbricated with respect to an upward flow, and the bombs show scattered distribution.

February 18, 2021, a flank eruption started on the north-western slope of the Klyuchevskoy Volcano (Kamchatka, Russia). Cinder cone was formed at the altitude of 2 850 m above sea level, from which a lava flow was spreading north-west. Having moved 1.2 km downslope, the lava flow entered the Ehrmann Glacier, which resulted in the formation of huge mud-stone flows. The latter made their way further north-east along the Kruten’kaya River bed and reached the length of about 30 km. The eruption brought onto the surface high-aluminous basaltic andesites typical of the Klyuchevskoy Volcano. By March 21, the flank eruption ended. It has been named after G.S. Gorshkov, associate member of USSR Academy of Science, famous Russian volcanologist.

The gravity method is a method often used in geophysical exploration. According to recent technological developments, data acquisition has evolved by utilizing satellite data and modeling, one of which is GGMplus gravity data. In this study, GGMplus gravity data will be used to map the distribution of maar and cinder cones in the Gunung Lamongan Region. To obtain the optimal local anomaly results of gravity data, a combination of power spectrum analysis and upward continuation filtering methods is carried out.ABL data contours are sliced, gravity anomaly data from each slicing path is processed using FFT so that the wave number and power spectrum values are obtained as well as the relationship graph between the two.The power spectrum analysis method provides window width data that is used as information on determining the height of the upward continuation method.The ABL contour map in the Gunung Lamongan region shows a range of gravitational field values between -20 mGal to 50 mGal. High anomaly values indicate the existence of Mount Lamongan which is dominated by intrusive rocks. The subsurface structure of the Gunung Lamongan region is thought to consist of tuff, lava, volcanic breccia, and lava. The existence of maar and cinder cones in the Gunung Lamongan area can be mapped from the contours of the local anomaly. Local anomaly contours are obtained from ABL data by connecting the two methods of filtering i.e power spectrum analysis and upward continuation. There are 10 cinder cones and 8 maar visible on the local anomaly contour map.

The Chaihe–Arxan volcanic field is situated in the Greater Khingan Range of northeastern China. The volcanic field consists of over 40 monogenetic cones. Yanshan is the youngest volcano in this area, with a reported age of 2 ky BP. The regions surrounding the volcano was subjected to a large fire in 2006, allowing researchers to determine the eruption history of the volcano. During a 2-week comprehensive field investigation, we found Yanshan volcano exhibits three types of eruption products: pyroclastic blanket, multi-crater scoria cone, and lava flow. The eruption process of this volcano has since concluded. Its eruption activity was initially ambiguous Strombolian eruption of the north crater, followed by sub-Plinian eruption of the east crater, and finally lava flow effusive events from the west crater. The Yanshan basalts are composed of trachybasalt and basalt. Geochemical analyses for major and trace elements suggest that the Yanshan basalts do not undergo significant crustal contamination but undergo olivine and pyroxene crystallization. Experimental melt calculations and the La/Yb versus Sm/Yb diagram indicate that the Yanshan basalts are derived from the melting of garnet peridotite. The Sm/Yb versus Na/Ti diagram illustrates that the initial melting depth beneath Yanshan is approximately 140 km, and the lithospheric thickness is approximately 70 km. These results support the existence of a high-temperature and fluid-rich plume at a depth of 10–12 km beneath the youngest volcanic chain where Yanshan is located, indicating the possibility of eruption of this volcano. Therefore, it is necessary to strengthen volcanic monitoring at Yanshan.

Recent subaerial volcanism at El Hierro Island (Canary Islands, Spain) consists of monogenetic volcanic fields. This volcanism generated cinder cones, tephra air-fall deposits, and lava flows. The lava flows reach several kilometres in length extending through shore platforms and, sometimes, penetrating under the sea level. The volcanic landforms of El Hierro convert it into a natural laboratory for topographic and morphometric modelling and lava flow simulations. We perform the modelling and simulation of the Montaña de Aguarijo eruption, a cinder cone at the NE rift. The associated lava flow channelled through a V-shaped ravine until reaching a cliff, where formed cascades. The flow spread at the cliff base over a platform before reaching the sea modifying the coastline. Different maps were designed to show the results, including the geomorphologic reconstruction of the area affected by this eruption and the lava flow simulations obtained with the Q-LavHA plugin. © 2021 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group on behalf of Journal of Maps., Financial support was provided by Project LAJIAL (ref. PGC2018-101027-B-I00, MCIU/AEI/FEDER, EU). This study was carried out in the framework of the Research Consolidated Groups GEOVOL (Canary Islands Government, ULPGC) and GEOPAM (Generalitat de Catalunya, 2017 SGR 1494).

La Poruna (21°53′S; 68°30′W) is a 140 m high scoria cone composed of pyroclastic material and an extensive basaltic-andesite to andesite lava flow that is up to 8 km in length. Automated mineralogical analysis describes a suite of porphyritic mafic samples, comprising olivine- and pyroxene-bearing rocks. Well-defined major element compositional trends, as well as trace and rare earth element characteristics (e.g. Sr/Y 96 ka) from San Pedro volcano exhibit similar isotopic characteristics, therefore evidence of similar magmatic processes. This new dataset clearly defines magma compositional changes during the La Poruna eruption (ca. 100 ka), revealing an increase in crustal contamination at shallow crustal levels for the younger San Pedro lavas (

A stratigraphic framework can be constructed through lithofacies description and interpretation. The application of this method in volcanic systems is a fundamental tool for understanding their evolution and eruptive dynamics and for establishing hazard assessments in active volcanic areas. This work presents and discusses a detailed stratigraphy of the Paredao Volcano, allowing the understanding of the lateral and vertical distribution of volcanic facies and the 3D geometry of the deposits, generating a model for the volcanism and discussing the erupting mechanisms. The Paredao Volcano is a scoria cone located in the southeast of Trindade Island and represents the youngest subaerial volcanic episode (Pleistocene) recorded in Brazil. Its stratigraphic organization indicates nephelinitic flows alternate with lapillistones and lapilli-tuffs of same composition at the base and a pyroclastic cone with nearly 200 m high above the sea level. Through lithofacies description and association 4 stratigraphic columns were constructed in scale 1:50, three of them at the Tartarugas beach (TRV-01, TRV-02, TRV-03) and the other one at the pyroclastic cone (TRV-04). The petrographic characterization of facies was carried through conventional optical microscopy. The stratigraphic analysis resulted in the distinction of seven lithofacies, divided into two coherent and five volcaniclastic (one autoclastic and four pyroclastic). The coherent lithofacies are of massive (Npm) and vesicular porphyritic nephelinite (Npv). Texturally, the lavas are holocrystalline and vesicular, composed by olivine phenocrysts in a very fine matrix of clinopyroxene, nepheline, zeolite and titanomagnetite, at times with phlogopite. The autoclastic lithofacies of nephelinitic breccia (Nb) is composed of fragments (2 mm–15 cm) of vesicular nephelinite and the pyroclastic ones are composed mainly of lapillitic scoria fragments with subordinate bombs and volcanic ash. The pyroclastic lithofacies are of massive lapillistone (Lm) and lapilli-breccia (LBm), planar stratified lapilli-tuff (LTp), and reverse grading lapillistone (Lrg). The lithofacies associations characterize ‘A’a, rubbly pahoehoe and pahoehoe flow types, distal and proximal pyroclastic deposits. The interpretation of the vertical and lateral facies distribution leads to the conclusion that the volcanism occurred with an initial phreatomagmatic stage, succeeded by a Strombolian stage (pyroclastic with primary fragments domain) and a final Hawaiian stage (lava flows domain).

The present study employs petrology, rock magnetics, and paleointensity on four lava flows (seven sites) of the El Jorullo volcano; a historical (1759–1766 AD) cinder cone in the Michoacan-Guanajuato Volcanic Field. El Jorullo lava flows cover an extensive area of ∼10.8 Km2, and a volume ∼0.35 Km3. Rock-magnetic experiments and microscopic observations reveal pseudo-single domain size Ti-poor titanomagnetite as the main carrier of magnetization in all sampled flows. Notably the calculated mean direction from all the sites show a slight westwards bias when compared against the secular variation global models. The mean paleo-direction for the El Jorullo historical eruption is: Dec = 2.5°, Inc = 37.5°, kappa = 214, α95 = 1.8, N = 31; the Virtual Geomagnetic Pole has Plat = 87° N, Plong = 307° E, Kappa = 260, A95 = 1.6; paleointensity data: 45.4 ± 3.6 μT; and Virtual Dipole Moment: 10.3 ± 1 × 1022 Am2. The paleodirections and the paleointensity values from these lava flows are well-constrained and reliable. These results allow to improve the accuracy and reliability of the global and regional secular variation models available for the last centuries.

Explosive basaltic eruptions have been documented in monogenetic volcanic fields, and recognizing the scales of their explosivity is important for understanding the full range of basaltic volcanism. Here we reconstruct one of the youngest eruptions in the Pinacate volcanic field (Sonora, Mexico) and estimate the volumes of the lava flows, scoria cone, and tephra units. The source vent of the eruption is Tecolote volcano (27 ± 6 ka, 40Ar/39Ar). There were two distinct episodes of tephra production, Tephra Unit 1 (T1) followed by Tephra Unit 2 (T2). T1 and T2 show different dispersal patterns, with T1 dispersed in an approximately circular pattern and T2 dispersed oblately trending SE and NW of the vent. Based on column height reconstructions and deposit characteristics, the T1-producing eruption was subplinian (15–18 km plume), with a calculated mass eruption rate ranging between 1.0 ± 0.6 × 107 kg/s and 2.2 ± 1.2 × 107 kg/s and corresponding durations between 79 ± 54 min and 38 ± 26 min, respectively. The T2-producing eruption was violent Strombolian (11 km plume) with a calculated mass eruption rate of 3.2 ± 1.4 × 106 kg/s and resulting duration of 193 ± 78 min. In addition to the two tephra units, Tecolote volcano produced seven morphologically distinct lava flows. The majority of lava volume production occurred before—and partly contemporaneously with—tephra production, and five small-volume lava flows were emplaced after pyroclastic activity terminated, indicating shifting and simultaneous eruptive styles. Of the total 0.23 km3 dense rock equivalent (DRE) erupted volume, the lava flows constitute the majority (0.17 km3 DRE), with 0.041 km3 DRE volume for the cone and a combined 0.026 ± 0.005 km3 DRE volume for the two tephra units. The geochemistry of the samples is consistent with that determined for other Pinacate rocks, which show a trend most similar to that of ocean island basalts and appears characteristically similar to other volcanic fields of the Basin and Range province.

From June to August 2015, Mt. Raung located at the east end of Java, Indonesia, erupted effusively with Strombolian activity at the intra-caldera cinder cone. The effused lava from the base of the cone entirely buried the caldera floor with a lava bed and ultimately formed a temporary lava lake. In this study, details of the eruption sequence and formation process of the temporary lava lake are analyzed based on a series of high-resolution images combined with the high-frequency thermal observation results of Himawari-8. The volume of effused lava was also estimated using a digital elevation model (ASTER GDEM) based on the lava bed bathymetry in the caldera and lava bed distribution at several points over the course of the eruption. The total effusion volume was estimated to be 7.5 × 107 m3, and the average effusion rate was 1.4 × 106 m3/day. The activity consisted of four stages. The Precursory Stage was characterized by low-level thermal anomalies, which are thought to result from high-temperature spots at the bottom of several pits formed in the buried vent, probably due to magma head partial exposure or gas emission. Pulses 1 and 2 were effusive stages that formed the lava bed. The pattern recognized in the time-series variation of thermal anomalies was confirmed to reflect the lava effusion rate using the volumes estimated in this study. The lava bed is divided into the Lower and Upper lava groups, which were generated in Pulses 1 and 2, respectively, except for the fine lobes formed around the margin of the Lower lava group. The Terminal Stage also showed low-level thermal anomalies, most likely caused by gas emissions. The intra-caldera cone grew to approximately 100 m higher than its initial height by mid-August and then collapsed into the conduit at the end of the Terminal Stage. The lava bed increased in thickness through lobe multi-layering and later through the addition of lava directly from the vent into the lava bed interior. Over the course of the lava bed growth, the bed outline nearly matched the caldera contours. Uplift of the lava bed surface caused lateral fluidization of the bed, and molten lava was extruded at the bed margins, forming fine lobes. This process enlarged the zone of fine lobes around the lava bed. Thus, the lava bed growth resulted in the appearance of a lava lake. In the middle of Pulse 1, a small amount of hot material was thrown onto the slope beyond the caldera rim. In the future, the caldera floor uplift caused by this activity (approximately 49 m) will increase the risk of erupted material ejection outside the caldera. In a comparison with the 2013–15 Nishinoshima eruption, which was a similar effusive eruption, Mt. Raung was shown to have predominantly large lobes over most of the lava bed, while in Nishinoshima, narrow medium-scale lobes occupied the majority of the surface. This may be attributed to the high effusion rate of lava for Mt. Raung, which was approximately seven times higher on average than the lava effusion rate for Nishinoshima.

Gran Canaria, like most of the Canary Islands, shows evidence for young basaltic volcanism in the form of cinder cones and valley-hugging lava flows. These landforms were of no particular use to th ...

The El Pozo Volcanic Complex, in the south-central Mendoza province, is formed by three maars, the first to be described in the Payenia Volcanic Province and one of the few examples in Argentina. The maars of El Pozo Volcanic Complex (1, 2 and 3) show large craters (0.97 km, 1.2 km and 0.96 km, respectively) and their depth is between 10 and 57 m below the pre-eruptive surface. Their deposits are described from the only outcrops that have been found, called El Pajarito and El Visitante. It was interpreted that the first maar to be formed would have been No. 2, from which only the deposits corresponding to El Pajarito (3.6 m) and the lower section of El Visitante (28 m) are preserved. We suggest that its shape is the result of lateral vent migration and coalescence of successive vents. Then, after a short break represented by the angular unconformity in the El Visitante section, the active vent would have shifted more to the W and the maar No.3 is thought to have been formed. The activity of this maar is represented in El Visitante upper section, with features resulting from the presence of water in the time of deposition. Maar No. 1 was probably active simultaneously with maar no. 3, with which coalesces but the lack of outcrops does not guarantee this affirmation. Towards the end of the eruptive cycle, depletion of water produced a change in activity from phreatomagmatic to Strombolian and effusive. This gave rise to the nested pyroclastic scoria cone, El Pozo cone, which lies in the maars' 1 and 3 craters floors. El Pozo cone is related to lava flows with a tumulus and the deposit of a lapilli-bearing tephra plume.

We find that volcanic hazards vary across the historically active Los Tuxtlas volcanic field (LTVF), with large scoria cones, and likely larger magnitude and intensity eruptions, concentrated in a NW–SE trending band and maars distributed at lower elevations. As eruptive processes vary in systematic ways across the LTVF that reflect the structure and topography of this volcanic field, spatial variations in eruption characteristics we identify are a valuable guide to future volcanic hazard assessments. The LTVF is located in a tropical climate near the coast of the Gulf of Mexico, isolated from the Trans-Mexican Volcanic Belt. We have identified 350 recent monogenetic edifices, mainly scoria cones and maars, in this approximately 100 × 50 km and mostly poorly accessible volcanic field. We compare morphologic traits among scoria cones and maars in the central and distal areas of the volcanic field using statistical analyses of volcano morphometric parameters obtained from Lidar images. Predictions, using the Kriging function, indicate areas most prone to future eruptions and likely morphologic characteristics of future volcanoes, which correlate with eruptive processes. Larger-sized scoria cones are preferentially located close to fault systems that define the center line of the NW–SE elongate volcanic field and likely are produced by eruptions with violent Strombolian phases. Some of these cones emplaced close to the NW-trending fault systems are associated with low-viscosity lava flows that reach > 10 km off the axis of the volcanic field. These are inferred to have particularly high effusion rates. Phreatomagmatic eruptions occur preferentially in the SW section of the volcanic field, a region which currently hosts a shallow ground water table near the contact with the Tertiary Veracruz basin sediment fill.

Few studies have focused on the post-eruption evolution of maar craters and associated lake level changes, although breaching of the crater rim poses mass-flow and flood hazards long after the initial eruption. Lake Pavin is a maar lake in the French Massif central formed by an eruption c. 6700 years ago. The maar is perched on the edge of a glacially-shaped valley and the rim overlooks the surrounding subdued landscape. The rim is breached to the north by an overflow channel, and to the south the maar has cut into the flank of the Montchal scoria cone and lava flows. Incision of the lake outlet led to the growth of an alluvial fan that pushed the Couze Pavin River towards the north side of the Gelat valley. Two lake terraces within the crater are used to determine stages in the evolution of the lake. The highstand Stage 1 terrace +18 m above the current lake level indicates that the post-eruption lake surface and volume was 15% and 38% larger than the present-day lake, respectively, prior to the 5-7th Century CE. The poorly preserved Stage 2 bench, +4.35 m on the west side of the natural dam, indicates that incision paused between Stage 1 and achievement of present lake level (Stage 3) before the 18th Century. Four units of streamflow deposits (c. 0.087 km2 in area and 0.14–0.18 km3 in volume) that formed the fan at the mouth of the outlet in the Gelat valley have been 14C dated to between the 9th and 16th Century. From the fan sedimentology, we infer that the lake level dropped slowly between highstand Stages 1 and 2, when the outlet cut down through the rim saddle. The lake level drop accelerated between Stage 2 and Stage 3 before the 14th Century, inducing small debris flows. The latter may have resulted from heavy rainstorms, but there is no evidence for catastrophic events. Stepwise downcutting of the north rim saddle was also governed by contrasted properties of the deposits forming the dam. The current lake level has been stable since at least the early 18th Century, but the long-term stability of the dam is at risk.

Krafla central volcano in Iceland has experienced numerous basaltic fissure eruptions through its history, the most recent examples being the Mývatn (1724‒1729) and Krafla Fires (1975–1984). The Mývatn Fires opened with a steam-driven eruption that produced the Víti crater. A magmatic intrusion has been inferred as the trigger perturbing the geothermal field hosting Víti, but the cause(s) of the explosive response remain uncertain. Here, we present a detailed stratigraphic reconstruction of the breccia erupted from Víti crater, characterize the lithologies involved in the explosions, reconstruct the pre-eruptive setting, fingerprint the eruption trigger and source depth, and reveal the eruption mechanisms. Our results suggest that the Víti eruption can be classified as a magmatic-hydrothermal type and that it was a complex event with three eruption phases. The injection of rhyolite below a pre-existing convecting hydrothermal system likely triggered the Víti eruption. Heating and pressurization of shallow geothermal fluid initiated disruption of a scoria cone “cap” via an initial series of small explosions involving a pre-existing altered weak zone, with ejection of fragments from at least 60-m depth. This event was superseded by larger, broader, and dominantly shallow explosions (~ 200 m depth) driven by decompression of hydrothermal fluids within highly porous, poorly compacted tuffaceous hyaloclastite. This second phase was triggered when pressurized fluids broke through the scoria cone complex “cap”. At the same time, deep-rooted explosions (~ 1-km depth) began to feed the eruption with large inputs of fragmented rhyolitic juvenile and host rock from a deeper zone. Shallow explosions enlarging the crater dominated the final phase. Our results indicate that at Krafla, as in similar geological contexts, shallow and thin hyaloclastite sequences hosting hot geothermal fluids and capped by low-permeability lithologies (e.g. altered scoria cone complex and/or massive, thick lava flow sequence) are susceptible to explosive failure in the case of shallow magmatic intrusion(s)., Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659, European Research Council http://dx.doi.org/10.13039/501100000781, Ministry of Business, Innovation and Employment New Zealand, deutsche forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659, Ludwig-Maximilians-Universität München (1024)

During continental rifting, strain and magmatism are believed to localize to narrow magmatic segments, while the rift margin is progressively abandoned. We integrate volcanological, geochemical, petrological and seismic data from the Ma’Alalta volcanic field (MVF) near the western margin of Afar, to show that the MVF is an active magmatic segment. Magmatism in MVF initiated with lava flows and large-volume, caldera-forming ignimbrites from a central edifice. However, the most recent magmatic activity shifted towards mafic lava fields, cinder cones and obsidian-rich silicic domes erupted from vents aligned NNW-SSE, defining a ~ 35-km-long magmatic segment. Along the same area, a NNW-SSE alignment of earthquakes was recorded by two local seismic networks (2005–2009 and 2011–2013). The geochemistry of the mafic rocks is similar to those of nearby axial volcanoes. Inferred magma storage depth from mineral geobarometry shows that a shallow, silicic chamber existed at ~ 5-km depth below the stratovolcano, while a stacked plumbing system with at least three magma storage levels between 9 and 24 km depth fed the recent basalts. We interpret the wide set of observations from the MVF as evidence that the area is an active magmatic segment, showing that localised axial extension can be heavily offset towards the rift margin.

International audience; Given the high eruption recurrence in the Michoacán-Guanajuato volcanic field (MGVF) in central Mexico, the birth of a new monogenetic volcano can be expected in the future. It is important, therefore, to reconstruct the past eruptions of its many different volcanoes, including estimates of lava flow emplacement times and their rheological properties. These studies define the range of possible future eruptive scenarios and are necessary to evaluate potential risk. The Rancho Seco monogenetic volcano, located in the central part of the MGVF (19°37′03”N, 101°28′21”W), was radiocarbon-dated at ~27,845 years BP. Its eruption initiated with a violent-Strombolian phase that produced a scoria cone and was followed by the effusion of at least seven associated andesitic lava flows, reflecting drastic changes in the eruptive dynamics. Effusive activity probably involved decreases in the magma ascent and discharge rates linked to efficient degassing in an open system. Lava chemical composition suggest an origin of partial melting of a subduction-modified hydrated heterogenous mantle wedge and textural and mineralogical analysis indicates significant crystal fractionation and minor assimilation of granodioritic basement rocks. High-resolution LiDAR imagery was used to estimate lava flow viscosities and emplacement times by following a morphology-based methodology. Results indicate that lava flow viscosities ranged from 105 to 109 Pa·s and emplacement durations between 32 and 465 days for the flow units considered (F5 and F6). The entire eruption may have lasted from 2 to 6 years with a mean effusion rate of 4 to 15 m3/s. Our results are also pertinent to archaeologists studying the architectural remains of Angamuco, a large urban pre-Hispanic site built on Rancho Seco's lava flows.

New stratigraphic, lithological and petrographic analyses of La Poruna scoria cone (21° 53′ S-68° 30′ W, Central Andes, northern Chile) allow the reconstruction of the eruptive sequence of this monogenetic cone. Petrographic and lithological characteristics allow us to identify three main lithostratigraphic units at La Poruna scoria cone. The first unit consists of agglutinated lapilli, spatter beds, and clastogenic lavas that are related to the construction of the cone. The other two units are associated with a lava flow field and consist of flow of andesitic composition, which differ both in their degree of weathering and in their development of channel, surface, and internal structures (e.g., levees, ogives, and joints). With these lithostratigraphic analyses, we interpret that the construction of La Poruna occurred during four main eruption phases involving Strombolian, Hawaiian, and transitional eruptive styles. Furthermore, differences in the degree of erosion, alteration, and weathering of the lithostratigraphic units in the lava field of La Poruna suggest that this flow field was formed during two eruptive events. The excellent outcrop conditions and preservation state of the volcanic products of La Poruna allow new stratigraphic insights that advance the wider and more general understanding and the dynamics of this important type of volcanism and the potential hazards of a scoria cone eruption. The polycyclic style of the eruption needs to be included in the hazards assessment of these centers type, especially when the cone is associated with structures that can be reactivated. This process could correspond to a second phase of activity, involving ash fall, bomb, and lava emission.

The mafic back-arc volcanism, uncommon in the Andean Central Volcanic Zone, is represented in the Puna region by late Miocene to Quaternary small monogenetic to polygenetic cinder cones and lava flows, as isolated or poorly clustered centers of basaltic andesitic to andesitic composition. Maars, tuff rings, and domes are also usual. This volcanism has a reduced representation in relation to the voluminous silicic ignimbrites and andesitic–dacitic stratovolcanoes that characterize the region. The scoria cones have moderate to low maximum slopes

Monogenetic volcanoes can yield eruptive suites displaying substantial complexity in compositional characteristics. The Bahariya monogenetic volcanoes (BMV) in the Western Desert, Egypt are a good example. They comprise complex stratigraphic deposits involving scoria cone, lava flows, and subvolcanic sills and dikes related to diverse eruptive styles. Whole-rock and mineral chemistry and 40Ar–39Ar geochronology are used here to document the petrogenesis, source characteristics, and evolution of the Bahariya volcanoes. The architecture of the BMV is the product of two alkali magma batches: pyroclastics and lava flows forming explosive scoria cone (batch 1) and subvolcanic sills (batch 2). The two batches show contrast in the concentrations of incompatible trace elements and REE as well as element ratios such as Nb/Yb, Gd/Yb, Nb/U, and Ce/Pb (36, 5.0, 44, 30 vs. 17, 4.0, 39, 24 for batch 1 and 2, respectively). New whole-rock 40Ar/39Ar dating displays consistent age of 23.71 ± 0.06 and 23.73 ± 0.01 Ma for magma emplacement of batch 2. Batches 1 and 2 share common LILE and LREE enrichments and HFSE depletions, analogous to a HIMU-like, mantle-derived OIB source described from other Paleogene–Oligocene intraplate magmatic provinces in North Africa and worldwide. Trace element modeling proposes a derivation of the Bahariya volcanoes from parental melts generated by 8–12% partial melting of garnet lherzolite and amphibole-bearing garnet lherzolite at 2.18 ± 0.33 and 1.77 ± 0.33 GPa for batch 1 and batch 2, respectively, across the lithosphere–asthenosphere boundary at c. 70–90 km depth (2.14–2.76 GPa). These sources had been earlier metasomatized by volatile-, LILE- and HFSE-rich fluid(s) originating from Neoproterozoic subduction or a Phanerozoic plume. Fractional crystallization involved olivine + clinopyroxene in both batches followed by Fe–Ti oxides + apatite in batch 2. Furthermore, crust contamination/assimilation was an irrelevant process at crustal level during magma ascend to the surface. Data results of the geo-barometric computations disclose two magma storage levels involving intermediate to lower crustal levels at c. 35 km (1.05 GPa) for batch 1 and mid-crustal level at c. 25 km depth (0.75 GPa) for batch 2. This study delivers proof that magmas emitted at Bahariya depression can undergo complex polymagmatic processes during their storage and passage in the crust, mainly due to the existence of a multilevel plumbing system. The origin of the BMV, as with other within-plate volcanoes in North Egypt, appears to be allied to extension-induced asthenosphere upwelling activated by limited exclusion of thickened lithospheric root under a passive rift tectonic regime coupled with the development of lithospheric thinning and continental breakup in North Africa.

Observations of active eruptions can provide insights into spatter and scoria cone formation. As Kilauea's 2018 East Rift eruption developed and the outflow of lava localized at Fissure 8, a spatte...

Bahariya monogenetic volcanic field is characterized by important geomorphological features (geomorphosites), namely, sub-circular maar-tuff ring, scoria cones, and domal-shaped tumuli. These geomorphosites constitute an asset for geoeducation, geotourism and miscellaneous social activities. They offer important knowledge into the paleoenvironmental and climatic factors that affected the style of volcanism at the occasion, and eventually shaped the diverse landforms found in the volcanic field. Bahariya Oasis is exclusive for its excellent locations where many volcanic heritages of high value give evidence of phreatomagmatic and effusive-controlled phases which formed volcanic landscapes under humid to dry climate. The geoheritage and archeological sites of early settlements are abundant in the Bahariya Oasis, accentuating the scientific magnitude of this region. There have been seven geosites recognized such as (1) the scoria cone, (2) the lava flows and their surface morphological features, (3) the pseudopillow fractures, (4) columnar joints, (5) peperites, (6) tumuli, and (7) rootless cones. These geosites coupled with other unique sites define the Oasis as global geopark. The latter will consider as an excellent logistical network to endorse volcanic geosciences and raise the economic growth in this part of Bahariya Oasis. The diverse geological characteristics at the Bahariya make this area a high volcanic geodiversity that can be used for geoeducational programs and geotourism. Excursions and research programs carried out by universities will contribute to enhanced geoconservation for local sustainable development. Currently, in the Bahariya region, tourism is not well developed, but it is recommended that, roads be improved to give better accessibility to the geomorphosites, and interpretative panels, informative brochures, multi-media presentations, seminars and workshops, scientific lectures, and postcards be produced to inform tourists about the geology of the region.

Based on a detailed geological map and stratigraphy aided by new 230Th/238U and 206P/238U age determinations we established the eruptive chronology of the Tres Virgenes Volcanic Complex (TVVC). The complex consists of three northeast-southwest aligned stratovolcanoes, which from older to younger are El Viejo, El Azufre, and La Virgen and associated cinder cones and domes. The alignment was fed from fissures that mark the southern trace of the left-lateral Cimarron Fault. The TVVC was built upon the basement rocks of the Peninsular Ranges Batholith (~99 Ma), the Santa Lucia Formation (21.6 Ma), the Esperanza basalt (7.6 Ma), and the 1.1 Ma ignimbrite of El Aguajito caldera. The TVVC began its formation at ca. 300 ka mainly with dacitic lava flows and domes that formed El Viejo volcano (4.2 km3). At around 173 ka, activity migrated to the southwest to build El Azufre volcano (3.8 km3) with the emission of dacitic lavas and several phases of dome construction and destruction with the generation of pyroclastic density currents. El Azufre's activity ended ~128 ka with the extrusion of the summit dome. At about 112 ka, volcanism migrated 4.2 km to the southwest to begin the construction of La Virgen Volcano through the emission of andesitic and dacitic lavas that built the largest cone of the complex until ~22 ka (31.2 km3). This volcano was built upon several stages of cone construction with the emission of lava flows and peripheral dacitic domes and cinder cones. Between 128 and 112 ka six cinder cones vented along the Cimarron Fault between the La Virgen and El Azufre volcanoes. By assuming a constant emission of magma the total volume of the TVVC (39 km3) was erupted at an average rate of 0.13 km3/kyr. Of this volume, effusive eruptions dominated the evolution of the complex (89%) of which 62% are dacites and 38% andesites. The TVVC rocks have compositions of 50–67 wt% in silica, and low-medium K (0.5–2.5 wt% K2O). Trace element signatures of the TVVC rocks (Sr/Y 2 km within the Peninsular Ranges Batholith as confirmed by geobarometry, aeromagnetic data, and the drill-holes of the geothermal field. Today, the Tres Virgenes geothermal field generates 10 MW of electricity although future exploration of several nearby areas may increase such capacity.

The Acoculco Caldera Complex (ACC) is located in the eastern part of the Trans-Mexican Volcanic Belt, Mexico. The ACC was formed 2.7 Ma, and since then, volcanic activity has persisted until 0.06 Ma, through the emission of domes, cinder cones, fissure lava flows and two ignimbrite eruptions dated at 1.2 and 0.65 Ma. The pervasive hydrothermal alteration in the central part of the ACC has motivated considerable geothermal exploration, however, none of it assessed the relation between the magmatic heat supply and the evolution of magmas, including their reservoir depth. Magmatic processes were investigated with petrography, major oxides-trace-element geochemistry, mineral chemistry and isotopic analysis. In addition, we performed a series of hydrothermal experiments in order to constrain the storage depth for the magma tapped 1.2 Ma during a reactivation of the caldera. We investigated the origin of magmas tapped during the eruptive history of the ACC, and the magmatic processes (magma mixing, assimilation and crystallization) that modified these magmas. After the caldera collapse 2.7 Ma, the local stress field was probably modified and allowed the ascent of peralkaline magmas through new plumbing systems. Such magmas mixed with calc-alkaline magmas and formed the post-caldera volcanism. Influx of new magma is considered as the probable heat supply that maintains the active magmatic system, whereas assimilation has been negligible, but yields insights about the depth at which processes have occurred. Our work suggests that there are either shallow storage zones (200–500 bars) where magmas crystallize and either erupt or stall and cool, or there are intrusive magmas unrelated to the ACC suite that have accumulated nearby and heat the reservoir magmas.

The small monogenetic Bayuda Volcanic Field (BVF; 480 km2), comprising at least 53 cinder cones and 15 maar volcanoes in the Bayuda desert of northern Sudan is one of a few barely studied volcanic occurrences of Quaternary age in Sudan. The exact age of the BVF and the duration of volcanic activity has not yet been determined. Furthermore, not much is known about the eruptional mechanisms and the related magmatic and tectonic processes that led to the formation of the volcanic field. In the framework of a larger project focusing on these points it is the purpose of this contribution to provide a first account of the general geology of the BVF volcanoes as well as a first description of a general stratigraphy, including a first description of their morphological characteristics. This was done by means of fieldwork, including detailed rock descriptions, as well as the analysis of satellite images (SRTM dataset at 30 m spatial resolution). The BVF cinder cones are dominated by scoracious lapilli tephra units, emplaced mainly by pyroclastic fallout from Strombolian eruptions. Many cones are breached and are associated with lava flows. The subordinate phreatomagmatism represented by maar volcanoes suggests the presence of ground and/or shallow surface water during some of the eruptions. The deposits constituting the rims around the maar volcanoes are interpreted as having mostly formed due to pyroclastic surges. Many of the tephra rings around the maars are underlain by thick older lava flows. These are inferred to be the horizons where rising magma interacted with groundwater. The existence of phreatomagmatic deposits may point to a time of eruptive activity during a phase with wetter conditions and therefore higher groundwater levels than those encountered historically. This is supported by field observations as well as the morphological analysis, providing evidence for relatively high degrees of alteration of the BVF volcanoes and therefore older eruption ages as suggested by some researchers. A Lower Holocene to Upper Pleistocene age is proposed.

A small, inconspicuous scoria cone in western Bohemia, known as Komorni hůrka Hill, played a crucial role during the controversy between Plutonists and Neptunists over the origin of rocks in the first half of the nineteenth century. The year 2017 represents the 180th anniversary of one successful resolution of this debate: at the instigation of J.W. Goethe, adits were dug into this volcano to access its feeding system in order to observe whether volcanoes were fed by burning coal seams, or feeder dikes of magma. The adits into Komorni hůrka Hill were the first large earth-works with a solely scientific goal and with no commercial mining purposes. The basaltic feeder exposed in the adits decided definitively in favour of the Plutonists after decades of ongoing arguments with the Neptunists. Here, we summarize the overall history of this small volcano. A recently conducted ground geophysical survey confirmed the position of historical adits, marked on several archive sketches. The geophysical data, comprising ground magnetometry, electric resistivity tomography and refraction seismic profiles, also revealed the internal structure of the volcano, including the position of the feeder dike and the geometry of a lava flow emitted from the crater. With the position of these historical adits confirmed by geophysical survey, excavations can safely reopen these historical earth-works and provide access to a wider public. Komorni hůrka could then serve as an educational geosite to exhibit the structure of a small monogenetic volcano, as well as illustrating a stage in the history of Earth Sciences.

The Sośnica Hill volcano is part of the Oligocene to Miocene (30.9–20.0 Ma) Strzelin volcanic field. It is located 100 km east of the Ohře Rift in the eastern part of the Fore-Sudetic Block, south of the town of Strzelin, Poland. Modern quarrying has exposed the sub-volcanic magma feeder system of the central part of the volcano and an extrusive volcanic succession that includes a 40 m thick sequence of lava flows and pyroclastic deposits that collectively form a complex scoria cone. Geophysical data (ground magnetometry and electric resistivity tomography (ERT)) reveal sharp linear anomalies that are interpreted to reflect normal faults dissecting the volcano. The ERT data map both high and low resistivity bodies, likely representing coherent clay-free dry rocks and partly argilized volcaniclastic deposits, respectively. Paleomagnetic data from 20 intrusive sites reveal two populations of reverse polarity site mean data; 11 sites are of low dispersion and yield a group mean direction that is discordant to the expected field direction, while six sites are highly scattered. Three sites did not yield interpretable results. We interpret the 11 sites as time-averaged field directions that are discordant to the expected field. The high dispersion of the remaining six sites are interpreted to indicate sub-volcanic deformation associated with the growth of the volcanic construct or multiple magma pulses over an extended period of time relative to secular variation. AMS data from 35 sites show a range of flow directions that vary across the quarry without an orderly pattern of fabric orientations. The flow pattern identified from dike paired margin data exhibits sub-vertical upward flow, sub-vertical downward, and moderately inclined northwest flow. Field observations and mapping indicate a complex development of the system in terms of styles of eruptive activity and structure of the final volcanic edifice. The activity included Strombolian and effusive phases, followed by phreatomagmatic, Hawaiian and again effusive eruptions. Such diversity of eruptive styles shows that the origin of the volcano is more complex than a simple, ‘textbook’ monogenetic scoria cone. Palaesoil on top of Strombolian deposits document a longer break in activity, after which eruptions resumed with different style; this is also not typical of monogenetic cones. The lateral variation in the volcanic succession suggests eruptions from several smaller, local vents. The complex subvolcanic magma flow patterns recorded in dikes match the variation of surface eruptive products and documents dynamically changing magma distribution paths in the near-surface and intra-cone part of the feeding system of the volcano.

The Manoteras volcano (Tortonian to Pleistocene, Calatrava Volcanic Field, Spain) is composed of a scoria and spatter cone surrounded by a field of pahoehoe lava. The volcanic cone is made essentially of vitreous lapilli-tuffs with intercalations of vitreous tuffs and spatter deposits, without any intercalations of lava flows. Erosion has uncovered an intra-cone plumbing system formed by coherent dykes and pyroclastic dykes (mixed-type dykes). This dyke swarm reflects processes of intrusion at the end of the eruption or even post-eruption. All the volcanic products are nephelinitic in composition. The main dyke is up to 3.4 m thick and has an exposed length of ~ 1000 m. It is composed mostly of coherent nephelinite with some pyroclastic sections at its northern extremity. This dyke is regarded as a feeder dyke of the volcano, although the upper parts of the dike have been eroded, which prevents the observation of the characteristics and nature of the possible overlying vent(s). Mixed-type dykes could also have acted as small linear vents and indicate that the magma fragmentation level during final waning stages of the eruption was located inside the volcanic cone. The pyroclastic deposits that make up the volcanic cone at the current exposure level were probably developed during a major phase of violent Strombolian style that formed the scoria cone, followed by a Hawaiian phase that formed the summital intracrater spatter deposit. Three central-type vents have been identified: one at the highest point of the remnant volcanic cone (summital vent), from where the earlier explosive eruptions took place, and the other two at the fringe of the cone base, from where emissions were only effusive. The lava flows were emitted from these boccas through the scoria cone feeding the lava field. The results obtained, based on careful field observations, add substantial complexity to the proposed eruptive models for small-volume basaltic volcanoes as it appears evident that there may exist and evolution through time from central conduit settings to fissure eruptions. Moreover, it is shown that intracone plumbing systems can integrate coherent and clastic dykes of variable thicknesses, which, in some cases could represent feeder dykes.

In the metamorphic Sanandaj-Sirjan Zone of western Iran, the “North Qorveh Volcanic Field” is constituted by Pleistocene scoria cones and associated deposits. Most scoria cones in the area display a simple structure resulted by Strombolian eruptions. Some of them are more complex, such as the Kuh-e Qarineh cone in where basaltic scoriaceous falls are underlain by felsic pyroclastic density–current deposits due to gas streaming at the base of eruption columns and are overlain by basaltic lava flows linked to basaltic fire fountains. Thus, it seems that the latter cones have been likely constructed by more or less violent Strombolian and then Hawaiian activities. Two types of enclaves have been found: gneissic xenoliths scavenged from the metamorphic basement and ultramafic–mafic (37–47 wt% SiO2) cumulates with the same paragenesis as the basaltic scoriaceous falls and lava flows. Three classes of cumulates were identified: (1) apatite mica hornblendite; (2) apatite hornblendite; and (3) olivine biotitite. Moreover, the mineral assemblage of basaltic rocks in the area (olivine (Fo79 − 83) + diopside + pargasite + phlogopite + Fe-Ti oxides ± plagioclase ± apatite) is very similar to lamprophyric facies. So, it seems that the parental magma was originated by mantle metasomatism. Although the felsic pyroclastic density–current deposits show a calcalkaline trend, the whole-rock and mineral chemistry of the basaltic rocks in the area imply an alkaline affinity. Also, the samples show subduction and continental collision signatures. Thus, the alkaline composition of this young volcanic centre in a metamorphic terrain could be explained by descending slab-break off and reactivation of small-scale convection at the lithosphere-asthenosphere boundary.

We present a rheological and morphological study of a Holocene lava flow emitted by a monogenetic cinder cone in the Cima Volcanic Field, eastern California. Our field observations focused on surface morphology, which transitions from smooth core extrusions near the vent to jagged ‘a’ā blocks over the majority of the flow, and on channel and levee dimensions. We collected airborne photogrammetry data and used it to generate a digital elevation model. From this, the total flow volume was estimated and surface roughness was quantified in terms of standard deviation of the real surface (5 cm resolution) from the software-generated 1 m-average plane. Sample textural analyses revealed that the near-vent portion of the flow is significantly more crystalline (ϕxtal = 0.95 ± 0.04) than the main flow body (ϕxtal = 0.66 ± 0.11). The rheology of Cima lavas was determined experimentally by concentric cylinder viscometry between 1550 °C and 1160 °C, including the first subliquidus rheology measurements for a continental intraplate trachybasaltic lava. The experimentally determined effective viscosity increases from 54 Pa·s to 1361 Pa·s during cooling from the liquidus (~ 1230 °C) to 1160 °C, where crystal fraction is 0.11. The lava viscosity over this range is still lower than most basaltic melts, due to the high alkali content of Cima lavas (~ 6 wt% Na2O + K2O). Monte Carlo simulations were used to account for and propagate experimental uncertainties, and to determine which rheological model (Bingham, power law, or Herschel-Bulkley) provides the best-fit of the obtained rheological data. Results suggest that Bingham and Herschel-Bulkley models are statistically indistinguishable from each other, and that both fit the data better than a power law model. By combining field observations and experimental results, we reconstructed the eruption temperature and few days-long emplacement history of the Cima flow.

The giant trough system of Valles Marineris is one of the most spectacular landforms on Mars, yet its origin is still unclear. Although often referred to as a rift, it also shows some characteristics that are indicative of collapse processes. For decades, one of the major open questions was whether volcanism was active inside the Valles Marineris. Here we present evidence for a volcanic field on the floor of the deepest trough of Valles Marineris, Coprates Chasma. More than 130 individual edifices resemble scoria and tuff cones, and are associated with units that are interpreted as lava flows. Crater counts indicate that the volcanic field was emplaced sometime between ∼0.4 Ga and ∼0.2 Ga. The spatial distribution of the cones displays a control by trough-parallel subsurface structures, suggesting magma ascent in feeder dikes along trough-bounding normal faults. Spectral data reveal an opaline-silica-rich unit associated with at least one of the cones, indicative of hydrothermal processes. Our results point to magma–water interaction, an environment of astrobiological interest, perhaps associated with late-stage activity in the evolution of Valles Marineris, and suggest that the floor of Coprates Chasma is promising target for the in situ exploration of Mars.

The Golden Trout Volcanic Field (GTVF) produced the only Quaternary eruptions of mafic magma within the southern Sierra Nevada block. Approximately 38 × 106 m3 of basalt, trachy-basalt, basaltic trachy-andesite, and basaltic andesite (50.1–56.1% SiO2, 1.1–1.9% K2O, and 5.4–9.1% MgO) was erupted from four vents within a ~ 10 km2 portion of the GTVF, which also includes rhyolite domes that are not considered in this study. The vents include, from oldest to youngest: Little Whitney Cone, South Fork Cone, Tunnel Cone, and unglaciated Groundhog Cone. Little Whitney Cone is a 120 m-high pile of olivine-CPX-phyric scoria produced during a Strombolian-style eruption overlying two columnar jointed lava flows. Tunnel Cone formed through a Hawaiian-style eruption along a 400 m-long north-south trending fissure that excavated at least three 25–65 m-wide craters. Crater walls up to 12 m high are composed of plagioclase-olivine-phyric spatter-fed flows that dip radially away from the crater center and crumble to form Tunnel Cone's steep unconsolidated flanks. South Fork Cone is a 170 m-high pile of plagioclase-olivine-phyric scoria that formed during Strombolian to violent Strombolian eruptions. South Fork Cone overlies the South Fork Cone lava, a 9.5 km-long flow (~ 12 × 106 km3) that reached the Kern River Canyon to the west. Scoria and airfall deposits originating from South Fork Cone are located up to 2 km from the vent. Groundhog Cone is a 140 m-tall cinder and spatter cone breached on the north flank by a 13 × 106 m3 lava flow that partially buried the South Fork Cone lava and extends 7.5 km west to Kern River Canyon. Incompatible trace element concentrations and ratios show vent-specific trends but are unsystematic when plotted in terms of all mafic GTVF vents, implying that GTVF basalts were derived from a lithospheric mantle source and ascended through thick granitic Sierra Nevada crust as discrete batches that underwent different degrees of crustal contamination, differentiation, and magma mixing. Clinopyroxene-liquid thermobarometry calculations of the oldest and most primitive GTVF sample indicate that most clinopyroxene crystals record nucleation conditions of 1172–1196 °C and 896–1115 MPa. These pressures correspond to depths equivalent to, or up to 10 km shallower than, the Moho in this region. Deposits from the oldest GTVF vents are more primitive and homogeneous in terms of major and trace element concentrations, phenocryst textures and compositions, and their general absence of crustal xenoliths and xenocrysts compared to younger eruptive products. The eruption rate of the GTVF (~ 0.05 km3/Myr) is two orders of magnitude less than neighboring and contemporaneous Big Pine and Coso volcanic fields to the north and east, respectively. We interpret these differences to result from a relative lack of strain in the GTVF region of the southern Sierra Nevada block, which limits magma accumulation and ascent.

Robust chronologies of Late Pleistocene and Holocene volcanic eruptions are vital for hazard analysis but accurate and precise dating of these events is often difficult. Here we apply various luminescence techniques to quartz and polymineral extracts from heated crustal xenoliths enclosed in scoria and volcanically heated bedrock in the Quaternary Eifel Volcanic Field (EVF), Germany. Consistent results from red thermoluminescence (RTL) and optically stimulated luminescence (OSL) of quartz and from post-infrared infrared stimulated luminescence of polymineral material demonstrate complete luminescence signal resetting during lava emplacement and sufficient signal stability. RTL and OSL age underestimation of one sample with independently known age from the lava contact zone could be eliminated by annealing before laboratory regenerative irradiation. The average luminescence age of 33.6 ± 2.4 ka for the Wartgesberg eruption is in good agreement with independent age control, while the average age of 15.5 ± 1.1 ka for the Facher Hohe scoria cone is much younger than previously assumed. This result represents the third youngest known eruption in the EVF. Our new data are in line with the hypothesized climate-controlled triggering of Eifel volcanism and confirm that active volcanism related to asthenosphere upwelling migrates from NW to SE in the EVF.

Red Crater volcano is one of several contemporaneously active vents on the Tongariro Volcanic Centre. Its history provides an opportunity to investigate the contrasting magmatic evolutionary paths of closely-spaced volcanoes. Rocks erupted at Red Crater over the last ~ 3.4 ka display typical subduction-related trace element and isotopic signatures. Those erupted pre-1.8 ka are medium-K andesites (SiO 2 ~ 59–62 wt%). They represent the most voluminous magmas and were emplaced in 5 lava flow events. An abrupt shift to the eruption of basaltic andesite (SiO 2 ~ 53–54 wt%) with less radiogenic Sr-Nd-Pb isotope ratios, occurred post-1.8 ka. This period comprised 6 smaller volume, lava flow episodes and the contemporaneous development of a scoria cone. Plagioclase phenocrysts in post-1.8 ka lava flows have resorbed cores with diverse textural and compositional growth patterns, as would be expected from the disruption of a crystal mush. They are similar to phenocrysts of the pre-1.8 ka lava flows. The post-1.8 ka plagioclase is distinguished from those in the older lavas by overgrowths with elevated An (~ 70–90), FeO and MgO contents, that mantle the resorbed cores (~ An 50–70 ). These rims are compositionally similar to groundmass plagioclase. This demonstrates that new mafic magma was intruded into the system, mixing with and entraining relic crystals from the older andesite system. Iron and Mg zoning patterns in the crystals are not consistent with significant re-equilibration via diffusion. Hence, the generation of eruptible magma during the last 1.8 ka required repeated mafic intrusion events. The emptying of the older andesitic magma reservoir early in the volcano's history removed buoyancy barriers to the direct eruption of more mafic magmas. This pattern of magmatism is not recorded at the contemporaneously active Ngauruhoe volcano, just 3 km to the SSW. Ngauruhoe rocks are compositionally distinct and are more heterogeneous in isotopic composition. Although mafic recharge is also evident, larger volumes of magma with more radiogenic compositions were erupted and the history of activity extends farther back in time than that of Red Crater. This is consistent with the development of a larger silicic reservoir beneath Ngauruhoe that could have acted as a buoyancy filter preventing direct eruption of mafic magma. The eruptive products of the two volcanoes reveal the diverging development of adjacent magmatic reservoirs that lack lateral connectivity at a scale in the order of 10 2 –10 3 m. There is limited literature on the comparative magmatic evolution of closely-spaced conduit/storage systems at arc volcanoes, reflecting the limitations of geochronological data at centennial and millennial timescales. However, such investigations provide insight into andesite assembly and the contrasting volcanism that could be expected in future activity.

Beneath subduction zone volcanoes, the parental magmas are thoroughly blended during temporary storage in the crust via repeated heating and mixing from new inputs of magma. To obtain a clearer picture of magma assembly, we employed a sub-crystal-scale Sr-isotope analysis, coupled with textural and geochemical data, on plagioclase phenocrysts in basaltic andesite and andesite erupted from the Tongariro volcanic complex, New Zealand. Deposits from two neighbouring vents were examined: (1) 0.3–3.4 ka lava flows of the polygenetic Red Crater volcano and (2) 26 ka pyroclastics of the monogenetic Pukeonake scoria cone. Despite the differences in eruptive styles and history of the two volcanoes, the plagioclase growth histories are similar. One common phenocryst type comprises of a resorbed core zone (variously, ~ An50–70) surrounded by a sieve-textured mantle/rim of higher An (~ 80), Fe and Mg contents. Other phenocrysts have resorbed calcic cores (~ An70–90). In situ 87Sr/86Sr analyses reveal a wide isotopic range (~ 0.7044–0.7060 for pre-1.8 ka Red Crater; ~ 0.7044–7057 for post-1.8 ka Red Crater; ~ 0.7047–0.7055 for Pukeonake). Most of the values are higher than that of the host bulk rock (87Sr/86Sr ~ 0.7049–0.7051 for pre-1.8 ka Red Crater; 0.7045–0.7046 for post-1.8 ka Red Crater; 0.7048 for Pukeonake). The variation within some individual phenocrysts is comparable to that of the entire population. The higher 87Sr/86Sr ratios are related relic phenocryst cores, indicating that their parental source was more radiogenic than the host magma. In contrast, their sieve-textured mantle/rim zones have lower 87Sr/86Sr ratios (~ 0.7045–0.7049), similar that of their host rock. These features record magma mixing. Less than 10% of phenocryst interiors are cognate (autocrysts) with the host rock based on their high 87Sr/86Sr ratio. Some phenocrysts are likely to be xenocrysts derived from the disintegration of deep crustal meta-igneous rocks. However, based on textures consistent with growth from a melt, the majority are antecrysts from intrusive forerunners and/or crystal mush zones, entrained during eruption or storage. Overall, the andesites are a product of crystal-poor magmas of mantle or lower crustal origin carrying phenocrysts from mostly crustal sources. The magma system likely comprised of a series of semi-isolated melt pods or crystal mush zones in a larger network of intrusions of various ages and states of solidification, possibly hosted in country rock of various compositions. Resorption of the sieve-textured mantle zones on the phenocrysts and growth of a normally zoned outermost rim represents a final period of fractional crystallization in the newly homogenised melt following the ascent and intrusion of mafic magma. Hence, the final tipping point to eruption may have involved crystallization-induced volatile exsolution and degassing.

Lava emplacement at monogenetic volcanoes has been seldom documented when compared to persistently active volcanoes such as Mt. Etna or Kilauea. To expand the scientific understanding of lava emplacement, and to help assess the hazards posed by monogenetic systems and of lava flows in general, we present an investigation of the lava field at Marcath volcano (~ 35 ka; Lunar Crater volcanic field, central Nevada, USA). Key data include lava surface characteristics as well as size and abundance data of rafted pyroclastic material derived from the source cone. Upon exiting the source crater, lava initially ponded in an upland saddle between Marcath and an older cone before breaking out to feed three lava lobes that spread out onto a flat valley floor below. Quantitative estimates based upon morphological parameters suggest time-averaged discharge rates of 40–100 m3 s−1, emplacement duration of 5–20 days, and bulk lava viscosities on the order of 106 to 107 Pa s in the main lobes. Sizes and distributions of 1021 mapped pyroclastic rafts suggest that the early stages of the eruption produced much of the total raft volume. The source of most of the raft material was likely the now-missing western portion of an early Marcath cone. After the initial breaching of the cone, the raft production rate likely kept pace with cone building over the eruption’s duration such that once the cone was breached on one side, it did not heal. Rafts were not always passive passengers on the lava: they had an important impact on lava morphology in specific locations, as they caused bifurcation of entire flow lobes and produced other flow features. The common occurrence of rafts in monogenetic lava fields suggests that incorporation of raft-lava interactions may be important in lava propagation models.

The southern Cappadocia shows a large variety of Quaternary volcanic landscapes, offering the opportunity to observe beautiful and generally fresh morphologies. These landscapes include two rhyolitic complexes (Golludag and Acigol), a huge composite volcano (Hasandag) and numerous monogenic vents, with scoria cones, domes and maars. Natural and anthropogenic sections show a large variety of lava flows and tephra layers. The precise study of this volcanic material allows reconstructing the volcanic and geomorphologic evolution of this area during the Quaternary, including modes of emplacements, chronology of the volcanic successions, morphological impacts on the landscapes. In addition, archaeological excavations in southern Cappadocia testify for the presence of ancient populations since the Middle to Upper Palaeolithic. During the Neolithic and Chalcolithic periods, the southern Cappadocia has been intensively occupied with permanent sites (Asikli Hoyuk, Musular, Tepecik Ciftlik, Kosk Hoyuk, etc.) as well as non-permanent sites devoted to mining and chopping of obsidian associated with some of the volcanoes.

In this study, three field programs have been conducted to determine the distribution and structure of volcanic landforms (lava flows, cinder cones, eruptive centers), and collect samples for analytical studies (age determination, mineral and whole composition, isotope geochemistry). The first expedition was to Harrat Lunayyir, where recent seismic activity has indicated the possibility for developing new volcanic systems. The second expedition targeted Harrat Hutaymah, as a remarkable area for providing an extraordinary range of mantle and crustal xenoliths, which are rock fragments carried up from great depths (40–70 km) by magmas that fed lava flows and cinder cones.

The Kamo Volcanic Field (KVF), a partly preserved Quaternary volcanic sequence of three small-volume basaltic volcanoes located about 10 km northwest of the Aira caldera in the Kagoshima graben in southwestern Kyushu, Japan. It forms part of the volcanic arc of Japan and consists of the Late Pleistocene Aojiki volcano and two Holocene maars: Sumiyoshiike and Yonemaru. Here, we report the first results of a combined lithostratigraphic and petrogenetic study of these three volcanoes. Eruptive products of Aojiki volcano comprise an initial scoriaceous tephra, a lava flow and scoria fall from the cone. Sumiyoshiike and Yonemaru maar products are mainly scoria fall and pyroclastic surge deposits, which are closely related in time and were principally emplaced by phreatomagmatic explosive eruptions. Major and trace element data of the eruptive products suggest four groups of magmas. Aojiki scoria (G1: SiO2= 50.3-51.4) are the most evolved, followed by Aojiki tephra/lava (G2: SiO2 = 48.1-50.7), while Sumiyoshiike (G3: SiO2 = 47.0-48.5) and Yonemaru (G4: SiO2= 46.3-48.5) are relatively less evolved. These magmas are derived from the same spinel bearing (lithospheric) mantle source previously metasomatized by subducting fluids and might have evolved in independent magma chambers mainly by fractional crystallization and crustal contamination except for G1 magma which may have suffered some associated mixing.

The local seismicity during the 2012–2013 eruption of Tolbachik Volcano and the 2008–2009 steam–gas eruption of Koryakskii Volcano is here considered as resulting from injections of magma that produced dikes, sills, and renewed activity at preexisting faults. We identified plane-oriented earthquake clusters in order to reveal the above zones using earthquake catalogs made at the Kamchatka Branch of the Geophysical Service of the Russian Academy of Sciences (KB GS RAS). Subsequent space–time analysis of these observations lends itself to the following interpretation. The November 27, 2012 Tolbachik lava eruption was preceded by an injection of magma resulting in a series of dikes trending west-northwestward in the range of absolute depths between –4 and +3 km in a zone situated southeast of the Ploskii Tolbachik Volcano edifice. The dikes penetrated into a nearly horizontal permeable zone at an absolute depth of approximately zero, producing sills and emplacing a magma-conducting dike along the top of the zone of cinder cones (the dip angle is 50° toward the azimuth 300°) 5.5 km from the epicenter of the initial magma injection. The summit steam–gas eruption of Koryakskii Volcano in 2008–2009 was preceded by magma filling a crustal chamber (the top of the chamber is at –3 km absolute depth; the chamber is 2.5 km across) close to the southwestern base of Koryakskii. Further, magma injection in a nearly north–south zone (7.5 by 2.5 km), the absolute depth between –2 and –5 km) in the north sector of Koryakskii Volcano was occurring concurrently with the summit steam–gas eruption. The injection of magma into the cone of Avacha Volcano (2010) produced sills (at altitudes between +1600 and +1900 m) and dikes (mostly striking northwest).

Assessment of volcanic hazards includes interpretation of ground deformation signal, which, at polygenetic volcanoes often results from the superposition of deformation due to pressure changes in the magmatic system and due to surficial processes such as cooling of emplaced lava. The deformation signal associated with emplaced lava is sometimes considered negligible if fields are decades old, but if the lava thickness is great, deformation may still be occurring, possibly leading to misinterpretation of the observed deformation. Here I evaluate the 2007–2011 ground motion of the 1943–1952 lava field of the Paricutin monogenetic cinder cone, Mexico. Interferometric Synthetic Aperture Radar (InSAR) time series reveal patchy subsidence restricted to the lava field and following linear rates up to 5.5 cm/year. There is a clear correlation between subsidence rates and topography suggesting a causal relationship with deposits or lava thickness. I estimate these thicknesses in the subsiding areas using pre- and post-eruption topographic maps and show that they reach up to 200 m. A numerical model for lava flow cooling was developed considering radiation and convection from the surface, conductive transfer inside the flow and to the ground, and vesiculation and latent heat generation at the top and bottom of the flow. The model shows that compaction induced by cooling of the thick deposits emplaced ~ 60 years ago explains the observed subsidence when conductive transfer to the ground is considered. These results demonstrate that thick deposits can keep deforming significantly even decades after their emplacement, emphasizing the importance of considering cooling processes when interpreting deformation fields at polygenetic volcanoes producing massive lava fields.

Lava flow hazard modelling requires detailed geological mapping, and a good understanding of emplacement settings and the processes involved in the formation of lava flows. Harrat Rahat, Kingdom of Saudi Arabia, is a large volcanic field, comprising about 1000 predominantly small-volume volcanoes most of which have emitted lava flows of various lengths. A few eruptions took place in this area during the Holocene, and they were located in the northern extreme of the Harrat Rahat, a close proximity to critical infrastructure and population living in Al-Madinah City. In the present study, we combined field work, high resolution digital topography and morphometric analysis to infer the emplacement history of the last historical event in the region represented by the 1256 AD Al-Madinah lava flow field. These data were also used to simulate 1256 AD-type lava flows in the Harrat Rahat by the MAGFLOW lava flow emplacement model, which is able to relate the flow evolution to eruption conditions. The 1256 AD lava flow field extent was mapped at a scale of 1:1000 from a high resolution (0.5 m) Light Detection And Ranging (LiDAR) Digital Terrain Model (DTM), aerial photos with field support. The bulk volume of the lava flow field was estimated at 0.4 km3, while the source volume represented by seven scoria cone was estimated at 0.023 km3. The lava flow covered an area of 60 km2 and reached a maximum length of 23.4 km. The lava flow field comprises about 20.9% of pāhoehoe, 73.8% of 'a'ā, and 5.3% of late-stage outbreaks. Our field observation, also suggests that the lava flows of the Harrat Rahat region are mainly core-dominated and that they formed large lava flow fields by amalgamation of many single channels. These channels mitigated downslope by topography-lava flow and channel–channel interactions, highlighting this typical process that needs to be considered in the volcanic hazard assessment in the region. A series of numerical lava flow simulations was carried out using a range of water content (0.1–1 wt.%), solidification temperature (800–600 °C) and effusion curves (simple and complex curves). These simulations revealed that the MAGFLOW code is sensitive to the changes of water content of the erupting lava magma, while it is less sensitive to solidification temperature and the changes of the shape of effusion curve. The advance rate of the simulated lava flows changed from 0.01 to 0.22 km/h. Using data and observations from the youngest volcanic event of the Harrat Rahat as input parameters to MAGFLOW code, it is possible to provide quantitative limits on this type of hazard.

Monogenetic volcanic fields usually comprise short-lived isolated volcanoes. However, new vents might build over or near to the older ones, resulting in the construction of complex, compound, nested, or overlapping volcanic structures formed by the superposition of individual monogenetic edifices. In the present study, we examine the case of Alchichica Maar volcano that cut through a series of pre-volcanic materials, including sheets of lava flows, pyroclastic deposits, paleosols, and scoria cone deposits. Major and trace elements are used to characterize geochemically each of the different pre-maar and maar units that integrate the Alchichica volcano, allowing to investigate the source composition, syn-eruptive, and crustal magmatic processes and the genetic relationship between the Alchichica maar and the underlying volcanic rocks. Typical lithologies are medium-K calc-alkaline rocks, including basaltic andesites for the lava flow and the scoria cone, and basalts for the maar units and the pre-maar pyroclastic unit. They also present slight variations in La/Sm, Ba/La, Zr/Nb, Ce/Yb, Ce/Pb, and Dy/Yb ratios suggesting different petrological processes such as variable amounts of partial melting in a heterogeneous spinel mantle, fractional crystallization, and crustal contamination during magma ascent. Our results reveal a polymagmatic activity, with different magma batches fed the pre-maar and the maar eruptions. They also allowed depict and confirm a time gap between the eruptive phases of the Alchichica maar formation, which is an add on the polycyclic character of the phreatomagmatic volcanism at this maar and previously described with the volcanostratigraphy examination. In addition, we conclude that the Alchichica maar cannot be defined as a polygenetic volcano; instead, it forms part of a cluster of Late Pleistocene to Holocene overlapped monogenetic volcanoes.

Barren Island, situated in the Andaman Sea, is the northernmost active volcano of the Sunda arc. The oldest known eruption of the volcano was during the period 1787–1832. After about 150 years of quiescence, volcanic activity resumed in 1991 and continues since then. The magmatic plumbing system of this volcano is largely unknown due to lack of geophysical experiments owing to its remote location. We report, for the first-time, time-series surface deformation measurements of Barren Island volcano from interferometric synthetic aperture radar (InSAR) during epochs 2007–2011 and 2015–2017. Line-of-Sight (LOS) deformation of −50 mm/yr during 2007–2011 at the cinder cone is interpreted as the co-eruptive pressure changes associated with the 2008–2010 eruptions. Bayesian inversion suggests a shallow magma reservoir at a depth of 578−100+300 m below the summit. The depth of the magma reservoir is shallower than that of other volcanoes of the Sunda arc, probably due to the extensional stress regime imposed by the oblique subduction. Based on the present studies and previous works, we propose a plausible source model for Barren Island volcano. We also discuss potential biases in the present source parameter estimation due to the lack of high quality InSAR data from both ascending and descending directions. Significant deformation (−15 to −150 mm/yr) observed along the lava delta of Barren Island volcano for both the epochs are interpreted as post-emplacement subsidence of the lava flow. Further, we characterise the lava flow including volcanic deposits by mapping its spatial extent and elevation changes during 1979–2000 and 2000–2017 periods using geodetic measurements.

We report on the Strombolian to Violent Strombolian eruption of Montana Grande which occurred between 789 and 725 BCE in the Guimar Valley on the NE flank of Tenerife island. The eruption produced a ca. 180 m-high scoria cone, a thick fallout deposit mostly dispersed southwest and a vast lava flow field that extends east of the cone, towards the coast, for 3.3 × 2.2 km. The eruption occurred in an unusual geodynamic context, outside the North West Rift and North East Rift zones and out of Las Canadas caldera which are the main geological structures of Tenerife, where the volcanic activity concentrated during the Holocene. The tephra and lava have a trachybasalt composition similar to products of the recent activity of Tenerife but characterized by a distinct trace element pattern (Ta depletion relative to Nb), that points to a distinct source for the magma feeding the eruption and an ascent history along the whole crust which is independent and different from the central feeding system of the Teide-Pico Viejo volcanic complex. The study of this eruption, which until now had been completely neglected, adds new significant data for the correct definition of volcanic risk in Tenerife.

The back-arc southern Puna region (south of ~24°S) in the Central Volcanic Zone of the Andes contains hundreds of Miocene to Quaternary mafic monogenetic volcanoes roughly distributed in several volcanic fields. Analysis of the geomorphology, morphometry, spatial distribution and age of 36 mafic monogenetic centers in the Peinado and Incahuasi fields, at the southwestern margin of the Puna plateau, gives insights on the links that mafic monogenetic volcanism can have with main and secondary structures, and the effects of degradation on scoria cone shape. Degree of preservation, morphometry and six new unspiked K-Ar ages indicate two distinct age groups, old centers > 2 Ma and young centers ≤ 1 Ma. The older mafic centers consist of degraded scoria cones and lava flows with an estimated cumulative bulk volume of 2.2 km3. The younger mafic centers display a variety of well-preserved landforms (scoria cones, lava flows, maars, tuff rings, domes) and have an estimated cumulative volume of 6.2 km3. Their distribution in a main NNE-SSW and secondary ENE-WSW trends suggests a control by the regional NNE-SSW striking Peinado and San Francisco fault systems in a dextral strike-slip configuration. Scoria cone and lava flow morphometries are similar in both fields, but a marked difference indicating hydrovolcanic activity is the presence of tuff rings, maars and tephra fallout deposits only in the Peinado field. Morphometric analysis of dated pristine and degraded scoria cones of the southern Puna region shows that parameters related to crater depth and inner crater steepness decrease consistently with age, suggesting that crater infilling is the degradation-related process that is most sensitive to age at scoria cones. In the southern Puna, high values of crater depth/crater width, crater depth/cone height and mean inner crater slope are indicative of a young ( 1 Ma) age, as young cones can have initially low values.

Twelve monogenetic volcanoes formed during the last 7 Ma within the Tarimbaro graben, northwest of the city of Morelia, in the central-eastern part of the Michoacan-Guanajuato volcanic field (Mexico). These include four scoria cones (Pelon, Tetillas, Jamanal, and Parastaco), four lava domes (La Cruz, Divisadero, Estadio, and Tetillas), two small shield volcanoes (Quinceo and Tetillas) and two lava flows (Cuto and Cerritos). Based on a detailed geological map and stratigraphy aided by new 40Ar/39Ar and 14C radiometric dates, and whole-rock chemical analyses, we established the eruptive chronology of these monogenetic volcanoes. These volcanoes were built upon four early Miocene successions of regional volcanism named Cuitzeo lavas (18.7 Ma), Cuitzeo ignimbrite (17.4 Ma), Atecuaro ignimbrite (16.8 Ma), and Punhuato lavas (16.3 Ma). Late Miocene to Pliocene activity consisted of the La Cruz, Divisadero, and Estadio domes and the Cuto lava flow (6.7–3.1 Ma). Pleistocene activity included the Cuitzeo fallout pyroclastic sequence (1.48 Ma), the Quinceo small shield volcano (1.36 Ma), the Pelon scoria cone (0.84 Ma), the Tetillas small shield volcano, two lava domes and a scoria cone (0.56–0.34 Ma), the Jamanal and Parastaco scoria cones and the Cerritos lava flow (0.11 Ma). Magma volumes from these volcanoes vary from

Aljojuca maar is located in the eastern Trans-Mexican Volcanic Belt, within the Serdan-Oriental Basin, which is characterized by Quaternary bimodal monogenetic volcanism. Aljojuca maar has an irregular shape, with an eastern embayment structure that forms an E-W alignment with at least three older scoria cones to the east. The crater walls expose a sequence of pre-maar volcaniclastic deposits, with a lava flow linked to the older scoria cones and a paleosol at its top; the latter indicates that a significant hiatus occurred between the growth of the scoria cones and the eruption of the Aljojuca maar, whose deposits overlie the soil. Strong interactions of the ascending magma with groundwater led to the emplacement of a ~30-m-thick maar sequence. Our detailed stratigraphic study shows that the eruption can be grouped into two main stages, comprising eight stratigraphic units deposited during five eruptive phases. The first stage reflects the development of the main crater (a maar sensu stricto) and is recorded by six stratigraphic units (from A to F). The eruption began with a strombolian pulse, followed by phreatomagmatic activity (unit A), forming dilute pyroclastic density currents. In the second phase, phreatomagmatic explosions prevailed with different degrees of fragmentation, from juvenile and lithic-rich lapilli fallout (unit B), to less diluted pyroclastic density currents (unit C), and a spatially restricted strombolian pulse. The third phase includes a main-vent enlargement event represented by a chaotic and heterolithic breccia (unit D). In the fourth phase, dilute pyroclastic density current deposits (unit E) dominate, with minor chaotic breccias (unit F). The second stage (fifth phase) includes the occurrence of a possibly fissural E-W structure, which formed a scallop in the eastern flank of the maar (eastern embayment structure), breaking the previously formed main crater's eastern flank and producing a 4-m-chaotic breccia (unit G) followed by the occurrence of a dilute pyroclastic density current (unit H), whose energy enabled the current to climb to the closest scoria cone. The migration of the explosive loci toward the eastern flank of the maar reflects a tectonic control by the dominant regional east-trending structural pattern. Several radiocarbon ages support that the eruption of Aljojuca took place between 2.7 ka (age of charcoal fragments under the ejecta ring) and ~2.2 ka (age of the oldest lake sediments in the maar crater). This has important implications for the hazard assessment of volcanism in this area, which had not been considered previously as a potentially active system.