Orals: Fri, 8 May, 10:45–12:20 | Room 0.96/97
Volcanic landforms and eruptive products can be effective proxies for paleoenvironment. The morphology of volcanic edifices can reveal whether they were constructed in subaerial or subglacial environments, while the physical characteristics of individual products indicate emplacement in wet or dry conditions. Polygenetic volcanoes with eruptive histories spanning glacial and interglacial periods therefore have the potential to record environmental change and it‘s influence on volcano evolution.
The deeply dissected flanks of the ice-capped Katla and Eyjafjallajökull volcanoes expose a >55 ka sequence of edifice-forming volcanic products. We combine detailed characterisation and geological mapping of the sequence with airborne photogrammetry surveys, examination of the geomorphology, and dating to reconstruct the eruption and emplacement processes, landform modification and paleoenvironments that have shaped this dynamic glaciovolcanic landscape. For example, intercalation of subglacial and subaerial deposits at the base of the sequence indicates a fluctuating ice margin 57-55 ka. Other distintive landforms include a 795 m-high peak dominated by bedded tuff and intruded with lobate lava bodies with an 40Ar/39Ar age of ~19 ka. The peak acted as a partial topographic barrier behind which an englacial lake accumulated. A lava delta prograded into the lake from 13-11 ka. A subaerial lava flow caps the delta and indicates a miniumum ice surface level ~ 850 m a.s.l. at the time of emplacement. The lava delta now forms a flat-topped, steep-sided plateau standing several hundred metres high above the landscape.
While these formations appear morphologically like volcanic vents or tuyas, detailed examination of the rock sequence, contact relationships and internal structures reveal they were once connected to the flanks of Katla and Eyjafjallajökull, and have been heavily modified by canyon incision. The lava ages reveal that canyon formation was rapid and likely faciliated by jökulhlaups associated with eruptions in a destabilising ice sheet. This is a crucial distinction for reconstructing the sequence of volcanic and glacial events, and the types of hazards that have occurred. These examples show how traditional geological mapping remains a fundamental tool for understanding volcanic landform evolution and hazard assessment.
How to cite: Cole, R., Gudmundsson, M. T., Gallagher, C., Jicha, B., and Óskarsson, B. V.: Geological and geomorphic evidence for eruption style, paleoenvironment and landform modification at Katla and Eyjafjallajökull volcanoes, Iceland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13283, 2026.
Multi-vent volcanic complexes in intraplate monogenetic volcanic fields provide key records of how karstification processes, evolving magma ascent pathways and inherited crustal discontinuities shape volcanic landforms. Located in the Middle Atlas Volcanic Field (MAVF) of Morocco, the Bouteguerrouine Volcanic Complex (BVC) is a coalescent system (~4 × 5 km) emplaced on a Liassic carbonate substratum and comprising 8 craters that include both phreatomagmatic and strombolian vents.
We combine field mapping and tephrostratigraphic logging with 0.5 m-resolution DEM morphometry and microstructural observations to link eruptive-style transitions to vent architecture and to evaluate the role of inherited structural trends of Middle Atlas chain in organizing vent migration.
Field analysis revealed evidence of polyphase evolution, marked by (i) an early hydromagmatic stage expressed by maar/tuff-ring deposits, including lithic-rich basal breccias and bedsets consistent with surge emplacement (locally preserved as discontinuous tuff-ring remnants and peperites), followed by (ii) a dominant strombolian phase constructed scoria and spatter cones and produced lava flows that either buried or locally truncated the underlying hydromagmatic deposits. These cross-cutting relationships provide a relative chronology markers documenting vent re-use, vent migration and progressive edifice coalescence.
DEM-derived metrics (crater elongation and breach azimuths, cone height and flank slopes) quantify vent geometry and migration patterns; Comparing our results with the Middle Atlas chain's inherited structural trends reveals the role of Quaternary tectonic evolution in guiding magma ascent pathways at the complex scale. In addition, microstructural observations indicate open-system magma evolution (zoned olivine and clinopyroxene, and disequilibrium reaction textures involving xenocrysts/xenoliths). These features are consistent with transient recharge and mixing during magma ascent and with variable vent dynamics.
Overall, the BVC provides a testable framework linking eruptive transitions, multi-vent growth and landform development, emphasizing coupled volcanotectonic and geomorphological controls in the Middle Atlas MAVF.
How to cite: El khaoutari, A., Chennaoui Aoudjehane, H., Agharroud, K., Balcon-Boissard, H., and Boudouma, O.: Multi-vent construction and eruptive-style transitions in the Bouteguerrouine Volcanic Complex (Middle Atlas, Morocco), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14961, 2026.
The stress field around a fluid supply source, such as a magma chamber, can be qualitatively explained by superposing the local stress field of radial compression and the regional tectonic stress field. However, stress field models incorporating both influences have not yet been proposed. In this study, we propose a new stress field model around a fluid supply source that accounts for regional stress, verify its validity by comparing it with natural data, and develop a stress field inversion method based on the new model.
The existing stress field model around a fluid supply source (McTigue, 1987) assumes the crust to be a semi-infinite elastic medium and approximately derives the stress field induced by a spherical pressurized cavity. In the new model, based on the principle of superposition, McTigue’s stress field is combined with a regional stress whose differential stress increases proportionally with depth. This formulation allows representation of anisotropic stress trajectory in the horizontal section.
To validate the new model in nature, we collected orientation data of clastic dikes intruded into the Miocene Tanabe Group in southwestern Japan. Stress inversion (Yamaji & Sato, 2011) was applied to the orientation data within subareas of several tens to hundreds of meters, and the stress state acting on each subarea was estimated. The results suggest that the orientation distribution of clastic dikes reflects both local stress associated with a fluid supply source (a mud diapir) located in the southern part of the study area and regional stress with a NNE–SSW-trending maximum horizontal compressive axis.
Based on the stress states detected in each block and their spatial locations, we estimated the stress field at the time of dike intrusion. In the inversion, the misfit between observed and modeled stresses in each block was assumed to follow a Fisher distribution, and a Markov chain Monte Carlo method was employed. As a result, WNW–ESE tension normal faulting regional stress was detected. The inferred location of the fluid supply source in the southern part of the study area is consistent with qualitative geological interpretations.
The results of this study provide fundamental insights for practical applications, such as identifying volcanic activity centers from dike or microseismic data and predicting the spatial extent of volcanic influence when dikes are discovered, contributing to disaster prevention/mitigation and geological disposal projects.
This study was carried out as a part of a supporting program titled "Program to support research and investigation on important basic technologies related to radioactive waste (2023–2025 FY)" under the contract with the Ministry of Economy, Trade and Industry (METI).
McTigue, 1987, J. Geophys. Res. 92, 12,931–12,940. Yamaji & Sato, 2011, J. Struct. Geol. 33, 1,148–1,157.
How to cite: Abe, N.: Stress field model around the fluid supply source associated with the regional stress state, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8715, 2026.
Understanding magma pathways and eruptive vent patterns is fundamental to deciphering how volcanic systems evolve in regard to their surface and subsurface structure, magma chemistry, and eruptive style. Recent studies have emphasized the critical role of the crustal stress field in controlling magma ascent, including magma trapping and prolonged storage in crustal volumes defined by stress field patterns. In extensional tectonic regimes, the influence of stress on magma pathways and vent distributions has been explored mainly across and along rift axes, showing that unloading and extension tend to focus magma pathways toward rift shoulders or rift tips, producing either distributed or localized vent patterns. These patterns are sensitive to basin geometry and the relative magnitudes of unloading and tensional stresses.
In this contribution, I first illustrate how unloading associated with extensional basins modifies the crustal stress field and promotes magma trapping at specific depths. Using stress-based models of magma propagation, I show that basin-related unloading can, in spite of extension, inhibit vertical ascent and favor the formation of laterally extensive, sub-horizontal magma storage zones, where magmas, deprived of their buoyancy, are effectively trapped. This leads to prolonged magma residence prior to eruption, creating the opportunity for cooling and chemical exchange with the host rock and successive magma batches reaching the stress trap. Upon eventual ascent, stress conditions drive dikes to propagate obliquely and then vertically, accelerating magma transport; together with volatile exsolution, this promotes conditions favorable for explosive eruptions. These results provide a mechanical framework linking tectonic forces, magma pathways, magma evolution, eruptive style and caldera formation in rift-related volcanic systems.
How to cite: Rivalta, E., Armeni, V., and Ferrante, G.: A mechanical perspective on magma trapping, storage and ascent in rift-related volcanic systems, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5248, 2026.
Santorini-Kolumbo is one of the most hazardous volcanic centres in Europe, as highlighted by its VEI-5 explosive eruptions of 726 CE and 1650 CE, and its bradyseismic crises of 2011-12 and 2024-2025. IODP Expedition 398 deep-drilled the volcano-sedimentary infills of marine rift basins at eight sites around Santorini to depths of up to 900 m below the sea floor, and integrated the core stratigraphies with a dense array of seismic profiles from eight expeditions to construct a high-resolution timeline of volcanic activity and to relate it to the basin-fill architecture and tectonic history. In this overview we show that the four drill sites analyzed to date reveal >200 Santorini and 19 Kolumbo tephra layers intercalated in marine sediments. The tephras were correlated chemically between sites, either as the products of individual eruptions or as packages of layers, with the onset of explosive activity at ~1 Ma. The rift basins contain several submarine volcaniclastic megabeds from the caldera-forming eruptions of Santorini and one from the Kos caldera. The megabeds formed when pyroclastic flows poured into the sea and transformed into subaqueous gravity flows. The thickest megabed succession is < 250 ky old and lies on a seismic reflection onlap surface that records a phase of rapid rifting. Sedimentation lagged behind subsidence during rapid rifting, creating bathymetric troughs that served as depocenters for the megabeds. Reconstruction of the basin subsidence history shows that the rift extension rate accelerated markedly about 350 ky ago. This increase in rifting rate preceded, and may have driven, the transition of Santorini from a prolonged state of effusive and moderate explosive activity (~550 – 250 ka) typical of arc stratovolcanoes to one of repeated caldera-forming eruptions (<250 ka). The earliest explosive activity at Kolumbo Volcano is recorded at 265 ka and coincides broadly with the explosive transition at Santorini, suggesting that activity at the volcanic systems is synchronized by tectonic stresses. The main stages of construction of the Kolumbo edifice broadly coincided with periods of caldera-forming silicic volcanism at Santorini, reflecting additional interactions and feedbacks on shorter timescales. The existence of connections between tectonic stresses, fluid pressures, and magma reservoirs of the two neighboring magmatic systems is consistent with concurrent ground movements, seismic swarms and dyke injection at Santorini-Kolumbo in 2024/25.
How to cite: Druitt, T., Metcalfe, A., Preine, J., Pank, K., Kutterolf, S., Hübscher, C., Nomikou, P., and Ronge, T. and the IODP Expedition 398 Scientists: New perspectives of volcanism at the rift-hosted Santorini-Kolumbo system (South Aegean Volcanic Arc), from IODP deep-drilling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14798, 2026.
Dyke intrusions and eruptions at nearby volcanoes can influence each other. However, the spatio-temporal connection of the magma storage and the dynamics of these events are rarely observed. We used InSAR, optical data, pixel offset tracking and seismicity to study two eruptions that occurred in the Erta Ale ridge within four months of each other causing caldera collapses. In November 2025, the Hayli Gubbi volcano erupted explosively sending an ash plume of ~14 km into the atmosphere. The eruption was preceded in July by a dyke intrusion and an eruption near the Erta Ale caldera. Dyking lasted 25 days and propagated southward for 36 km along the axis of the Erta Ale ridge, intruding a total of ∼0.4 km3 of mafic magma. The dyke also intercepted nearby magma reservoir, including a shallow (1.5 km depth) sill below Hayli Gubbi, causing minor uplift. Interestingly, Hayli Gubbi did not erupt until four months later, in November when InSAR shows that the contraction of a source under the Erta Ale caused the caldera collapse and simultaneous explosion and collapse at Hayli Gubbi. The July-November events suggests that the magmatic systems of Erta Ale and Hayli Gubbi are connected and that along axis dyke intrusion is a possible mechanism feeding other magma chambers ultimaltey triggering eruptions. We suggest that mafic magma was injected in Hayli Gubbi in July and again in November. Possible magma mixing with the residing melt occurred leading to the Haily Gubbi eruption. This is consistent with separate explosions and two plumes of likely different composition during the eruption (Ayalew et al., in preparation).
CP and ALR are supported by the Space It Up project funded by the Italian Space Agency (ASI) and the Ministry of University and Research (MUR) under contract n. 2024-5-E.0 CUP n. I53D24000060005.
How to cite: Pagli, C., La Rosa, A., Keir, D., Ayele, A., Wang, H., Rivalta, E., and Lewi, E.: Eruption triggering from connected magma storage at the Erta Ale ridge (East African Rift), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14411, 2026.
Campi Flegrei caldera is an active volcano located in southern Italy, which is experiencing renewed uplift phenomena since 2005. This phase has also been characterized by an increase of seismicity, which, mainly since 2021, has experienced relatively high magnitude earthquakes.
In this work we analyze the ground displacements induced by the 1 September 2025 seismic swarm, whose main shock registered a magnitude (Md) of 4.0 in an area affected by a previously investigated uplift deficit.
This event has been analyzed by applying Differential SAR Interferometry (DInSAR) techniques to multi-sensor and multi-frequency SAR data. Indeed, we exploited acquisitions carried out by the Copernicus Sentinel-1 constellation (operating in C-Band), the Italian COSMO-SkyMed (CSK) and COSMO Second Generation (CSG) satellites operating in X-Band, as well as the SAOCOM-1A/B constellation of the Argentinian space agency, operating in L-Band. Furthermore, we benefited from an acquisition campaign carried out by the Capella Space SAR sensors (X-Band) operating in a Mid Inclination Orbit (MIO) configuration, thus allowing us to investigate the displacement component also along the North-South direction.
Such large data availability allowed us to compute a detailed picture of the displacements affecting the Earth surface across the earthquake, providing a significant contribution to the comprehension of the caldera dynamics, and opening new perspectives in active volcano monitoring scenarios.
This work has been partly funded by the Italian DPC, in the frame of INGV-DPC (2022–2025) and IREA-DPC (2025–2027) agreements: this paper does not necessarily represent DPC official opinion and policies. This research was also partially funded by HE EPOS-ON (GA 101131592) and the European Union-NextGeneratonEU through the following projects: MEET - PNRR - IR00000025; ICSC - CN-HPC - PNRR M4C2 Investimento 1.4 - CN00000013; GeoSciences IR – PNRR M4C2 Investimento 3.1 - IR00000037; Sustainable Mobility Center - MOST - PNRR M4C2 Investimento 1.4 - CN00000023; BAC MITIGATE - PNRR RETURN - PE00000005.
How to cite: Casu, F., Bonano, M., De Luca, C., De Martino, P., Di Vito, M. A., Giudicepietro, F., Lanari, R., Macedonio, G., Manunta, M., Monterroso, F., Pappalardo, L., Roa, Y. L. B., and Striano, P.: Mapping the ground displacements related to the 1 September 2025 seismic swarm at Campi Flegrei (Italy) caldera through multiple SAR sensors, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14024, 2026.
Hydrothermal alteration can lead to weakening of volcanic rock, decreased slope stability and increased erosion, therefore creating potential mass-wasting hazards at volcanoes. The mechanical weakening may affect rock compounds, selected lithographic layers, or occur along fracture zones, with serious consequences for the evolution of volcanoes. Therefore, understanding the processes and interactions at the intersection of faults and hydrothermal systems is critical for assessing slope instability and the potential for failure. Here, we investigate these interactions at the Profitis Ilias lava dome on Nisyros Island (Greece). Nisyros has a complex volcanic history, including caldera-forming eruptions, extrusion of large rhyodacitic domes inside the caldera, and recurrent high-magnitude seismic activity that continues to shape the island. The most prominent dome, Profitis Ilias, rises up to ~700 m and is located at the intersection of major fault zones and an active hydrothermal system at its base, making it particularly susceptible to alteration-driven weakening. To investigate the impact of hydrothermal alteration on the stability of the dome in this particular setting, we combined optical and thermal satellite and drone-based remote sensing, image analysis, and rock-mechanical field experiments. We used Pleiades data to identify the spatial extent of hydrothermal alteration effects based on rock discolourization, indicative of hydrothermal alteration, by applying Principal Component Analysis. High-resolution optical and infrared drone surveys further constrained the distribution and intensity of hydrothermal activity. Our results show that hydrothermal activity and alteration penetrate deeply into the Profitis Ilias dome, affecting about ⅓ of its surface area. Thermal activity and alteration are observed laterally 500 m away from the eruptive centres at its base into the dome, and up to 300 m altitude above the caldera floor. A comparison with other hydrothermal areas within the caldera reveals that, although features such as Stefanos crater are visually prominent and frequently studied, hydrothermal activity at the base of Profitis Ilias is more extensive and exerts a strong impact on rock integrity. The affected part of the dome exhibits enhanced erosion and morphological evidence of weakening and destabilisation. To evaluate this, we performed rock mechanical field tests employing a Schmidt hammer and sampled rocks to measure their petrophysical and mineralogical properties in the laboratory. Rock mechanical field tests of representative endmember samples from fresh to altered dome rocks generally show strength reductions by over 66% for altered material. Similar measurements along transects at the eastern base of Profitis Ilias flank reveal the same significantly reduced strength relative to fresh dome rock, confirming substantial mechanical weakening of the dome's base. Considering the current deformation pattern on Nisyros, which outlines Profitis Ilias dome in the southeast and northeast along the main tectonic trend and the Mandraki fault, further investigation of dome stability is warranted. In particular, the combined effects of seismic activity, fault movement, and hydrothermal circulation beneath the eastern flank of Profitis Ilias may pose an elevated risk of slope instability.
How to cite: Müller, D., Walter, T. R., Nomikou, P., Nikoli, E., Zorn, E. U., Amelung, F., Lang, M., Troll, V. R., Heap, M. J., and Harnett, C.: Hydrothermal activity and impact on flank stability at the Profitis Ilias dome, Nisyros (Greece), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11660, 2026.
The renewed start and funding of the CARG project in volcanic areas have enabled new surveys and refinements of data on the volumes and extents of ignimbrites across the Roman Magmatic Province (RMP). To date, the investigation has focused particularly on the Roccamonfina volcano (Sheets 416 Sessa Aurunca and 417 Teano) and the Bracciano caldera (Sheet 364 Bracciano). The project is enhancing field data from areas already surveyed in past decades, while integrating new models and technologies to obtain more accurate quantifications of erupted magma volumes and a consequent re-evaluation of eruption magnitudes. Preliminary results indicate that the volume of some ignimbrites increases by more than one order of magnitude, suggesting that many other ignimbrites within the RMP may have been significantly underestimated, such as the Brown Leucitic Tuff and the White Trachytic Tuff pertaining to the Roccamonfina volcano. This reassessment potentially characterizes the RMP as an ignimbrite flare-up system, comparable to some of the largest and most impactful volcanic provinces worldwide, such as the Taupo Volcanic Zone. In this framework, new field and literature data, borehole stratigraphy, and GIS-integrated methodologies were combined to refine the bulk volume, areal extension, and magnitude of a case-study ignimbrite, with the aim of developing a standardized procedure for computing and integrating field surveys applicable to all ignimbrites.
How to cite: Frontoni, A., Gualda, G. A. R., Bonamico, A., Cioni, R., Conticelli, S., Sepulveda Birke, J. P., and Giordano, G.: CARG-based (Sheet 416, 417, and 364) volume reassessment for the caldera-forming, VEI 6/7 ignimbrites along the Roman Magmatic Province, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18452, 2026.
The transition and coexistence of large polygenetic volcanoes and monogenetic volcanic fields represents a key challenge in understanding crustal magmatism and volcanic evolution across active tectonic regions worldwide. This duality is strikingly exemplified in central Mexico. Here, the active polygenetic volcano Popocatépetl, coexists with the Chichinautzin Monogenetic Volcanic Field (CMVF), characterized by numerous small cones and lava flows reflecting short-lived, episodic eruptions. Although both volcanic styles are extensively documented individually, the fundamental tectonic and structural factors controlling their coexistence and transtition remain poorly understood. Our study aims to understand the influence of regional tectonic stress orientation and local faulting in interpreting the mechanisms that governs eruptive style transitions.
We integrated high-resolution structural mapping, remote sensing, and a 30-year seismic record (1994–2025). Fault and lineament patterns were derived from LiDAR Digital Elevation Models (DEMs) and Sentinel-1 SAR imagery, processed through slope, azimuthal, and contour analyses. These datasets were correlated with volcanotectonic (VT) earthquake records from Popocatépetl and CMVF to assess the spatial and temporal distribution of seismicity in relation to fault systems.
Our results delineate two major tectonic domains: (1) NW–SE and NE–SW fault systems characterizing the Popocatépetl volcano; and (2) a predominant E–W system defining cone alignments within the CMVF. Monogenetic cones in the CMVF align preferentially along E–W and NE–SW faults, reflecting a prevailing N–S minimum horizontal stress that facilitates direct magma ascent. In contrast, Popocatépetl is dissected by multiple, interacting, high-angle fault systems, including the active Tlamacas (NE–SW) and Nexpayantla (NW–SE) faults. The majority of pre-eruptive and co-eruptive VT earthquakes cluster along these structures, confirming their critical role in magma ascent, storage, and edifice segmentation.
We conclude that the coexistence and transition between polygenetic and monogenetic volcanism in central Mexico are fundamentally governed by the complexity and orientation of regional and local stress fields. In the CMVF, single stress regimes create efficient pathways for rapid magma ascent, favoring monogenetic activity. At Popocatépetl, intersecting and structurally complex fault systems induce magma trapping and long-term storage, driving polygenetic evolution.
How to cite: Sandoval García, M. and Martin-Del-Pozzo, A. L.: What controls the transition from monogenetic to polygenetic volcanism? Structural insights into the coexistence and transition between Chichinautzin Monogenetic Volcanic Field and Popocatépetl volcano, Mexico., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-574, https://doi.org/10.5194/egusphere-egu26-574, 2026.
Dokdo and Ulleungdo are volcanic edifices developed in the East Sea and show a clear contrast in their formation ages and evolutionary processes. The Dokdo volcano is an eroded volcanic edifice characterized by a flat summit at a water depth of approximately 200 m, forming a guyot-type morphology with small islets. The summit area reaches ~84.6 km² and is larger than the subaerial area of Ulleungdo. Approximately six levels of submarine terraces are developed on the summit, reflecting repeated Quaternary sea-level fluctuations. Bedrock exposure is dominant in the northern summit, whereas the southern part is sediment-rich, and an east–west alignment of small craters suggests the directional control of late-stage volcanic activity. The Dokdo volcano can be subdivided into a flat summit, a steep flank, and a gently sloping base. The flanks are characterized by submarine canyons and ridges with various orientations. Slope analysis indicates very steep gradients of up to ~27–30° along the canyons, implying repeated sediment transport and mass-movement processes. In the northern basal area, small cone-shaped positive reliefs are observed, and backscatter data indicate a mixture of exposed bedrock and sediment-covered surfaces. In contrast, Ulleungdo represents a relatively young, single-cone submarine volcano with a central volcanic island and steep flanks descending to depths of ~2,200 m. Radial lava ridges and lava fields are developed down to ~200 m water depth, while submarine canyons and debris lobes formed by repeated slope failures are concentrated between 600 and 1,200 m. The volcanic base consists of deep-sea sediment fans formed by gravity flows and turbidity currents, and only two levels of submarine terraces are developed on the continental shelf, in clear contrast to the multi-level terraces of Dokdo. Between Dokdo and Ulleungdo, the Anyongbok Seamount, with a summit depth of ~473 m, shows a pointed conical morphology without a wave-cut platform and a dominant north–south ridge. The concave summit geometry suggests the presence of a collapsed crater. Based on radiometric ages and geomorphic characteristics, the submarine volcanic edifices in the East Sea are inferred to have formed sequentially from Dokdo to Anyongbok Seamount and finally to Ulleungdo. These contrasting geomorphic features provide important constraints on the timing, eruptive styles, and spatiotemporal evolution of submarine volcanism in the East Sea.
How to cite: Kim, C. H., Choi, S. Y., Kim, W. H., Do, J. D., and Lee, B. G.: Submarine Geomorphology and Evolution of the Dokdo and Ulleung Volcanic Edifices in the East Sea, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2387, 2026.
Karthala (Ngazidja Island, Comoros archipelago), an active basaltic volcano in the Indian Ocean, provides an excellent natural laboratory for studying the geomorphic evolution of a rapidly evolving caldera complex. Eruptive events in 2005–2006 reached a VEI 3 and emplaced fresh tephra and lava across the summit area, covering the cratered region and creating a time-zero surface for tracking post-eruptive erosion and drainage network development. Karthala’s craters are also shaped by mass-wasting processes, evidenced by landslide deposits in the craters that are visible in satellite and aerial imagery.
In this study, we construct a geomorphic chronology that spans 76 years using a combination of photogrammetry from a 2025 Unoccupied Aerial System (UAS) survey, Pléiades satellite imagery (2015, 2024), and orthorectified historical photographs (1949, 1961). This interval includes significant eruptions in 1952, 1965, 1972, 1991, and 2005-2007. We primarily focus on geomorphic change since the 2005–2006 eruptions, measuring erosion within the tephra-mantled summit region and mapping the temporal evolution of fluvial channel networks. By tracking the development of the drainage network, we can precisely constrain landscape response times and quantify the timescales at which volcaniclastic material is mobilized and redistributed in the landscape. In addition, we evaluate crater rim retreat and map collapse structures through time to explore how mass wasting interacts and competes with fluvial processes. Together, this work provides constraints on the timescales and relative importance of erosional processes that shape Karthala’s summit region between eruptive events, while placing its recent evolution in the context of crater changes that have occurred over decadal timescales.
How to cite: Guryan, G., Gourbet, L., Zorn, E., Villeneuve, N., Delcher, E., Soulé, H., Mogne Ali, M., Said Abdallah, C., Mohamed, W., and Mlanaoindrou, Q.: Geomorphic Evolution of Karthala’s Summit Caldera: Insights from Photogrammetry, Satellite Imagery, and Historical Aerial Photographs , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11515, 2026.
This preliminary study addresses the architecture of the magmatic plumbing system in southeastern El Salvador, where a cluster of recent monogenetic volcanic centers is spatially associated with the Intipuca Fault. This fault is part of the active shear zone located at the volcanic arc accommodating the right lateral motion of the fore-arc sliver with respect to the Caribbean plate in the context of the Cocos plate subduction in the Middle America Trench. The Intipuca fault acts as a link between the El Salvador Fault Zone (ESFZ) and the extensional domain of the Gulf of Fonseca and the Nicaraguan depression.
Four representative lava samples were analysed: three from monogenetic volcanoes emplaced along the fault and one from the underlying Pliocene stratovolcano of the Bálsamo Formation. Detailed petrography, electron microprobe analyses of phenocryst and groundmass minerals in each sample, and Ar/Ar geochronology were performed.
Preliminary results reveal mineralogical and textural differences between lavas from the monogenetic cones and the stratovolcano. The latter are dominated by plagioclase, with abundant small olivine and minor, but large (phenocrystic) pyroxene, and lack hydrated minerals. Some plagioclase macrocrysts display abundant disequilibrium textures, including resorbed plagioclase cores and sieve textures, suggesting prolonged crustal residence and magma recirculation under dry conditions.
Monogenetic lavas are characterized by abundant pyroxene meso- and macrocrysts. Plagioclase shows a range of sizes, some crystals showing disequilibrium features while others are apparently in equilibrium (continuous oscillatory zoning and euhedral shape Olivine is subordinate, commonly with oxidized rims and replacement coronas of pyroxene and plagioclase. Opaque minerals are also common, and minor, subhedral green amphibole occurs locally. The occurrence of hydrated minerals in the monogenetic lavas reflects rapid magma ascent along the Intipuca Fault, which likely acted as a preferential conduit preserving fluids derived from Cocos Plate subduction.
Similar spatial associations between monogenetic volcanism and transtensional faults have been documented in fault systems with comparable orientations near the Gulf of Fonseca. Likewise, monogenetic alignments are identified in association with segments with a dominant E–W strike (between N90°E and N110°E) that characterizes the El Salvador Fault Zone (ESFZ). This supports the idea that strike-slip fault systems play a fundamental role in modulating magma plumbing architectures and controlling the spatial distribution of monogenetic volcanism in subduction-related volcanic arcs.
How to cite: Comas, N., Álvarez-Gómez, J. A., de Ignacio, C., Martínez-Díaz, J. J., and Hernández, W.: Structural control on monogenetic volcanism along the Intipuca Fault, Central America Volcanic Arc, El Salvador, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11915, 2026.
In south-western Martinique (Lesser Antilles), the basaltic lava flow and associated strombolian cone of Pointe Burgos transect the porphyritic dacitic lava dome of Morne Champagne, which has been dated to 617 ± 52 ka (Germa et al., 2011). A striking characteristic of the basaltic lava is an unusually high abundance (~4%) of large quartz crystals reaching up to 2 cm. These have previously been interpreted as xenocrysts incorporated into the basaltic magma through mechanical mixing with a shallow, cooled dacitic reservoir at an approximate 9:1 basalt–dacite ratio. Support for this interpretation includes resorbed plagioclase phenocrysts with reaction rims, commonly regarded as indicators of crystal remobilisation. However, the eruption products lack other textural features typically associated with magma mixing. Moreover, the quartz crystals display atypical morphologies, extensive internal fracturing, and occur as apparent void-fillings within the basalt, prompting a reassessment of their origin.
To better constrain the timing and mechanism of quartz incorporation, we investigated both the eruption age of the basaltic lava and the formation history of the quartz crystals. K–Ar dating of the basaltic groundmass yields an age of 379 ± 25 ka, indicating that the basalt erupted ~240 ka after the dacitic dome it crosscuts. This substantial time gap implies that the shallow dacitic reservoir would have been fully solidified during basalt ascent, a scenario in which entrainment of dacitic enclaves might be expected but is not observed.
Thermoluminescence (TL) dating provides a means to estimate the time elapsed since mineral crystallisation or cooling to ambient temperature, rendering it well suited to evaluate whether the quartz formed contemporaneously with the basaltic eruption or represents a later generation of minerals (substitution minerals or hydrothermal void fillings). Moreover, TL can inform on thermal conditions during signal acquisition through the thermal stability of selected TL signals. We applied red TL measurements using multiple dose determination protocols to calculate an apparent age, which yielded internally consistent results. Dose-rate calculations account for the grain-size distribution of the quartz xenocrysts, radioelement concentrations and the erosional evolution of the site.
Apparent TL ages range from ~104 ka assuming no erosion, to ~122 ka for ~100 m of surface erosion, each with an ~17% uncertainty. New LA-ICP-MS geochemical data obtained from three quartz xenocrysts provide further evidence for a magmatic formation environment, lending support to the magma mixing hypothesis. The younger TL ages relative to the K–Ar eruption age may thus reflect partial thermal resetting of the TL signal due to prolonged hydrothermal activity. Kinetic parameters derived from the TL data enable forward modelling of thermal scenarios compatible with the observed ages. Together, the geochronological, kinetic, and geochemical results allow us to reassess the origin of quartz in the Pointe Burgos lava and to explore the post-eruptive hydrothermal evolution of the system.
References
Germa, A., Quidelleur, X., Lahitte, P., Labanieh, S., Chauvel, C., 2011. The K–Ar Cassignol–Gillot technique applied to western Martinique lavas: a record of Lesser Antilles arc activity from 2 Ma to Mount Pelée volcanism. Quaternary Geochronology 6, 341-355.
How to cite: Schmidt, C., Germa, A., Quidelleur, X., King, G., and Jaimes-Gutierrez, R.: Constraining eruption age and quartz formation in a basaltic lava flow (Martinique) using trapped-charge and geochemical methods , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14547, 2026.
It is important to accumulate research examples on the spatial distribution of volcanic conduits and dikes under volcanic edifices that served as magma migration pathways, and eruptive volume of past activity, for risk assessment in volcanic disaster prevention. Particularly for volcanoes where the distribution of volcanic conduits and the eruptive volume of activity have not been clearly elucidated in detail, assessing their risk is difficult. Therefore, developing a quantitative and uniform assessing method applicable to each volcano is desirable. However, determining the distribution of volcanic conduits and dikes under volcanic edifices is challenging. Furthermore, estimating the eruptive volume of volcanic activity, requires detailed geological surveys, leading to insufficient estimates for some volcanoes.
The topography of a volcanic edifice is generally thought to reflect the location of magma intrusion associated with volcanic activity and its history (e.g., Nakamura, 1977). Therefore, we are developing a method to determine the predominant orientation of radial dikes under volcanic edifices and evaluate the long-term stability of central conduit locations using topographic analysis with GIS and 10m DEM (Nishiyama et al., 2023). Furthermore, we are attempting to develop a method to estimate the location of a center of activity and the eruptive volume of its activity using topographic data. The development of these topographic data-based evaluation methods is expected to provide useful objective baseline data for conducting detailed investigations on volcanoes that have not yet been studied in depth. This presentation introduces the content of our attempts using topographic analysis.
This study was funded by the Ministry of Economy, Trade and Industry (METI), Japan as part of its R&D supporting program for the geological disposal of high-level radioactive waste (JPJ007597).
[References] Nakamura, 1977, JVGR., 2, 1-16. Nishiyama et al., 2023, JSEG, 64(3), 98-111.
How to cite: Nishiyama, N., Kato, Y., Kawamura, M., and Umeda, K.: Attempt to estimate the center of activity and scale of Quaternary volcanoes through topographic analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15548, 2026.
The Lessini Mountains volcanic district (Venetian Prealps, Italy), belonging to the Veneto Volcanic Province, is mainly composed of Paleogene basaltic volcanics in complex stratigraphic and tectonic relationships with a Meso-Cenozoic sedimentary succession of a shallow-marine environment. The geological framework was shaped by extensional tectonics, with N–S-trending faults such as the Castelvero Fault, which separates the mafic rocks to the east from the carbonate lithologies to the west. The volcanic succession is characterized by a relative lithological homogeneity of basic volcanic products and by discontinuous outcrops due to dense vegetation and agricultural cover. Consequently, detailed reconstruction of the internal stratigraphy based on field data alone is challenging and requires further investigation to identify stratigraphic reference horizons. Overall, the succession records a transition from submarine to subaerial volcanism (Barbieri et al., 1991; Brombin et al., 2019). The lower portion is characterized by basaltic deposits emplaced in a marine environment (i.e., hyaloclastites to lava flows of fissural eruptions), frequently intercalated with Nummulitic Limestones which testify to phases of quiescence of the volcanic activity. The upper portion reflects the establishment of predominantly subaerial conditions, with the growth of shield volcanoes. Above the last nummulitic level (the Roncà Horizon), marking the base of the upper part of the volcanic sequence, the internal stratigraphy remains poorly constrained, as no laterally continuous stratigraphic markers have been recognized so far. This study focuses on this part of the volcanic succession, exposed along the ridges between Alpone Valley and Agno Valley, through the integration of remote-sensing analyses and detailed field observations. In recent years, the increasing availability, quality, and spatial resolution of remote-sensing data have made geomorphological analyses based on Digital Terrain Models (DTMs) an increasingly important complement to traditional geological investigations. Among the available visualization techniques, the Red Relief Image Map (RRIM) method has proven particularly effective in highlighting subtle morphological variations in volcanic terrains (Chiba et al., 2008; Favalli & Fornaciai, 2017). Within the framework of the CARG Project (Sheet 124 – Verona Est), RRIM-based geomorphological analysis integrated with detailed fieldwork provides new constraints on the stratigraphic reconstruction of the upper volcanic succession of the Lessini Mountains. A key result is the recognition of a decametre-thick volcaniclastic sedimentary level, mapped as the Cortivo Unit, clearly detectable in RRIM by its association wiht areas of lower slope gradients. This unit records a significant phase of volcanic quiescence, during which erosion, transport, and deposition processes led to the reworking of previously emplaced basaltic rocks. It therefore represents a stratigraphic hiatus and a marker horizon that subdivides the succession into a lower unit predating and an upper unit postdating the Cortivo Unit. Future geochemical and petrographic analyses and radiometric dating will allow calibration and refinement of the reconstructed stratigraphic framework.
How to cite: Cavallina, C., Sonia, S., Magli, A., Lucchi, F., José Pablo, S., Matteo, R., and Giulio, V.: Insights into the Eocene stratigraphic succession of the Lessini Mountains volcanic district by integrating field geology and geomorphological interpretation of Red Relief Image Maps from high resolution DTM (CARG Project, Sheet 124, Verona Est, Italy), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20022, 2026.
For decades, the Hallmundarhraun lava has been categorized as a historic lava, i.e. postdating the Landnám tephra layer (LNL) from AD 877. In the summer of 2024, the LNL was found on top of the lava, somewhat unexpectedly. In 2025, approximately twenty test pits were excavated to corroborate this initial finding. In all cases, the presence of the LNL was confirmed.
In connection with this study, a sample of barren plant remains was collected from beneath the lava and submitted for radiocarbon (¹⁴C) dating in Aarhus, Denmark.
The LNL is a widespread, two-coloured tephra, consisting of a lower light-coloured unit (c. 0.5 cm thick) of fine silicic pumice and an upper olive-green unit (1.5–2 cm thick) composed of basaltic glass shards. The LNL is one of the most important marker tephra layers in Iceland. It was found close to the lava surface, commonly separated from it by a 1–3 cm thick soil layer, although in some cases the soil cover was thinner.
In total, six distinct tephra layers were identified within the soil cover of the Hallmundarhraun lava. Samples from all layers were analysed chemically using an electron microprobe. The tephra layers younger than the LNL are, in descending order, H-1766, K-1721, H-1693, and H-1104. The oldest tephra layer identified is a black Katla tephra lying directly on top of the lava, with no intervening soil layer. This suggests that the Katla tephra and the lava are close in age.
A literature review was conducted to identify information that might constrain the age and distribution of this Katla tephra. Although the results were not conclusive, a possible correlation was identified with a widespread Katla tephra known as Hrafnkatla. This tephra has been identified in ice cores from the Greenland Ice Sheet and dated to AD 763 based on annual layer counting. The Katla tephra overlying the Hallmundarhraun lava may correlate with the Hrafnkatla tephra; however, as two other Katla tephra layers of similar age have been identified in soils and lake sediments, this correlation remains uncertain.
Taking all available evidence into account, the results indicate that the Hallmundarhraun lava most likely formed during the period AD 760–780. The radiocarbon dating supports this interpretation. Previously, the lava was thought to have formed between AD 910 and 950. The Hallmundarhraun eruption therefore predates the Norse settlement of Iceland in the mid-to-late 9th century, effectively excluding the possibility of eyewitness observations or contemporaneous written accounts.
How to cite: Sigurgeirsson, M. Á.: Revised age of the Hallmundarhraun lava, West Iceland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20945, 2026.
Mount Etna, one of Earth's most active volcanoes, rises to an elevation of 3,400 meters. Its eastern flank extends seaward, descending to approximately 1,500 meters below sea level and creating a total vertical relief of nearly 5,000 meters. While it is known that Etna's offshore flank is highly mobile, the seafloor morphology and associated structures remain poorly understood.
During the 2024 RV METEOR cruise M198, high-resolution microbathymetry data were collected using an Autonomous Underwater Vehicle (AUV), and rock samples were dredged from distinctive morphological features. Using new AUV microbathymetry, we characterise a stiff layer that forms a narrow canyon in the Valle di Archirafi, featuring high relief and rough surfaces exposed by the erosion of overlying marine sediments. This layer is also forming in the upper part of the Amphitheatre, a chain of cliffs overlooking a gentler slope. The layer is characterised by a chaotic, high-amplitude facies in the seismic lines, which can be followed from the Valle di Archirafi to the Amphitheatre. Dredging during the M198 cruise enabled sampling phyric lavas in the upper part of the Amphitheatre and chemical analyses suggest cooling in a subaerial environment. These findings imply more than 600 m of subsidence of the entire area (42 km2). The area is located between 4 and 8 km from the coastline and lies directly beneath the Giarre wedge, which exhibits the highest sliding velocity on the eastern flank. This suggests that the offshore part exerts a strong pulling force on the northern part of Etna’s mobile sector and is thus key to understanding the dynamics of the onshore sector. In line with the onshore block structure inferred by geodetic methods, our new findings support a decoupling of a shallower block riding on top of the larger southeastern mobile flank. Finally, based on existing knowledge of Etna’s edifice, our new offshore interpretation, and existing seafloor morphology constraints, we propose an extended map of the offshore flank thickness. These new data necessitate a revised interpretation of the submarine structural model and challenge existing paradigms regarding the mobile flank.
How to cite: Mayolle, S., Urlaub, M., H. Hansteen, T., Madrigal, P., Campbell, M., Furst, S., Bonforte, A., and Gross, F.: Etna’s submarine flank morphology and basement: new insight from microbathymetry and revised structural interpretation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13865, 2026.
Extensional tectonic regimes often host volcanoes that produce highly hazardous, caldera-forming explosive eruptions. An example is the Santorini-Kolumbo volcanic centre on the continental South Aegean Volcanic Arc. The volcanic centre includes Santorini caldera, the submarine polygenetic Kolumbo Volcano to the northeast of Santorini, and the linear zone of more than 20 smaller volcanic cones making up the Kolumbo Volcanic Chain. It is one of the most active eruptive centres on the South Aegean Volcanic Arc and experienced a period of unrest in 2024-2025. IODP Expedition 398 deep-drilled the volcano-sedimentary infills of submarine half-grabens around Santorini and on the western flank of Kolumbo in order to produce a high-resolution eruptive chronostratigraphy for the volcanic field, ground-truth seismic stratigraphy, and to extract an integrated timeline of interactions between the neighbouring volcanoes and volcano-tectonic couplings. In the new, more complete volcanic record, we: (1) recognise a transition of Santorini from moderately explosive, arc stratovolcano behaviour (~570 – 250 ka) to repeated caldera-forming behaviour (<250 ka), (2) identify 19 explosive eruptions of the KVC beginning at 265 ka with a lifespan-averaged recurrence time of explosive activity of ~6 k.y. (but as low as ~1 k.y. in certain time periods), (3) observe that the three main phases of edifice construction at Kolumbo (ca. 265–193 ka, 24 ka, and 0.4 ka) broadly correspond to the periods of caldera-forming eruptions at Santorini (186 ka – 177 ka and 22 ka – 3.6 ka). By ground-truthing seismic stratigraphy through core-seismic integration, we also produce a unique high-resolution record of volcanic activity and lithospheric extension for the volcanic field. This allows us to show that Santorini’s caldera-forming eruptions all lie above a seismic reflection onlap surface that records a phase of rapid rifting. This phase of rapid rifting may have amplified the normal internal dynamics of the magmatic system driving the transition of Santorini from a prolonged state of arc stratovolcano behaviour to a state of repeated caldera-forming eruptions. In addition, the birth of Kolumbo coincided with the transition of Santorini to highly explosive activity, possibly due to joint interactions with the regional lithospheric stresses. Through our new integrated record, we show a possible example of rift modulation of an arc magmatic system on the 104-105 yr timescales typical of caldera cycles and the coupling of neighbouring volcanoes on 104 yr timescales.
How to cite: Metcalfe, A., Druitt, T., Pank, K., Kutterolf, S., Preine, J., Nomikou, P., Hübscher, C., and Ronge, T. A. and the IODP Expedition 398 Scientists: Temporal linkages of explosive activity on the South Aegean Volcanic Arc related to changing lithospheric stresses, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17938, 2026.
The establishment of continuous volcanic time series is a key to understanding the volcanic evolution and behaviour of arc systems and volcanic complexes. Yet the establishment of continuous records is often hindered by incomplete volcanic archives on land due to erosion or inaccessibility of volcanic deposits. Growing steadily over the past decades, the field of marine tephra studies has shown great potential in overcoming these issues. As marine drilling techniques advance, they now enable the recovery of continuous and undisturbed marine sediment records, often even extending the volcanic onland records significantly further back in time. Drilling close to volcanically active environments, like volcanic arcs, provides the most complete eruptive archive possible and therefore allows us to unravel the volcanic and magmatic behaviour of volcanic systems over geologically long periods of time. Furthermore these long and continuous records enable multi-disciplinary studies, such as the establishment of volcano-tectonic or volcano-climate relationships.
IODP Expedition 398 drilled the marine sediments in the basins of the Christiana-Santorini-Kolumbo Volcanic Field (CSKVF) with the aim of expanding our knowledge of its volcanic evolution, and its interaction with tectonics and climate. The CSKVF belongs to the South Aegean Volcanic Arc (Greece), and particularly Santorini has been known for its highly explosive volcanism and caldera-forming eruptions since c. 250 ka that laid down the Thera Pyroclastic Formation (TPF). Before that, Santorini’s volcanic activity has been described as mainly effusive to weakly explosive forming the Peristeria stratocone (c. 530-430 ka) and the Early Centres of Akrotiri (c. 650-550 ka). However, IODP Expedition 398 identified a large submarine rhyolite deposit, the Archaeos Tuff (AT), interpreted as the product of a highly explosive submarine eruption of Santorini occurring at c. 765 ka, clearly pushing the boundaries of the unkown.
Here, we present the revised <765 ka tephrochronostratigraphy using the marine basin sediments drilled during IODP Expedition 398. Geochemical fingerprinting of tephras has enabled the identification of all known Plinian TPF eruptions, as well as numerous “new” explosive volcanic events within the TPF but also beyond. We have identified a total of 298 eruptions derived from Santorini and Kolumbo, and the established volcanic time series shows multiple tempos of arc volcanism, each about 250-300 kyr long. The eruptions range between magnitudes M2 to M6 throughout the record. However, the period <250 ka clearly stands out in terms of volcanic productivity and has produced about 3x more cumulative magma mass compared to the period 765-250 ka.
Our record fills the currently existing gap between Santorinis AT eruption at c. 765 ka and the onset of the TPF, and shows that Santorini was continuosly producing (highly) explosive eruptions. Furthermore, our findings highlight the importance of complementary and multi-disciplinary studies to reveal the most complete picture of arc volcanism.
How to cite: Pank, K., Metcalfe, A., Kutterolf, S., and Druitt, T. and the IODP Expedition 398 scientists: New insights on explosive volcanism at Santorini (South Aegean Volcanic Arc) based on marine sediments drilled during IODP Expedition 398., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18317, 2026.
