Displays

Mt. Gamalama has a history of volcanic tsunamis that have occured in 1608 and 1840. Regarding its geomorphology, Mt. Gamalama has very steep flanks, and landslides entering the sea could be the potential mechanism of tsunami generation which could threaten the coastal population and submarine infrastructure in the vicinity of Mt. Gamalama.

The potential volumes and types of landslides are estimated by a study of the Mt. Gamalama instabilities using the Generalized Hoek-Brown failure criterion which is applied in Slide2D (Rocscience), a 2D slope stability program using limit equilibrium methods. This procedure will result in a so-called Factor of Safety or FoS which represents a value of the Mt. Gamalama slope stability level.

The critical FoS values ranging from 1.945 to 3.361 have been obtained for four sections i.e., north, south, west and east side of the Mt. Gamalama edifice and are considered in relatively stable condition. These values hold for a static condition only under the force of gravity and in the absence of any volcanic activities. The application of seismic coefficients of 0.103 and 0.658, magma pressure of 2-17 MPa, and various angles of a dyke intrusion decreases the Mt. Gamalama stability and might cause landslides. Based on posture parameter analysis of modeled landslides, the landslide volumes could reach 10⁶ -10⁹ m³. Furthermore, regarding the morphometric characteristic parameter analysis, the landslide mobility could enter the Molucca seaand generate tsunamis.

Keywords: Gamalama, volcanic instability, volcanic landlsides, volcanic tsuamis

How to cite: Saaduddin, S., Neuberg, J., Thomas, M., and Hill, J.: The Mt. Gamalama Instability in Generating Landslides in Ternate Island, Indonesia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-893, https://doi.org/10.5194/egusphere-egu2020-893, 2020.

The Palinuro volcanic chain is located nearly 80 km offshore the Campania coasts (Italy), in the southern sector of the Tyrrhenian Sea. As many as 15 distinct volcanic edifices have been recently detected that covers a 90 km long and 20 km wide belt. The associated volcanism is still poorly understood but the presence of shallow seismicity and active hydrothermal activity suggest that this large volcanic complex is still active. Specific sectors of the chain show the presence of ongoing slope instability and thus the chance of mass movements cannot be ruled out in case of seismic or volcanic activity. In this work, a stability analysis for typical seismic loads in such a volcanic area has been performed through a revised limit equilibrium approach. In the revealed weaker sections, three mass failures of different scales have been reconstructed and their motion has been calculated by means of numerical models. The tsunami produced by each slide has been simulated, and considerable waves have been found in two of the three hypothesized scenarios. For the biggest slide of 2.4 km³, waves as high as 10 m could reach portions of the Calabria coasts with consequent hazardous impact.

This study belongs to a series of works focused on the volcanoes of the Tyrrhenian Sea that are very many and still poorly investigated. Considering scenarios involving mass movements of different sizes with distinct characteristics and based on geomorphological features seems to be a viable strategy to evaluate the tsunami hazard in the region.  

How to cite: Gallotti, G., Ventura, G., Armigliato, A., Zaniboni, F., Pagnoni, G., Wang, L., Passaro, S., Sacchi, M., and Tinti, S.: Stability analysis and tsunamigenic mass-failure scenarios in Palinuro volcano complex, Tyrrhenian sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8270, https://doi.org/10.5194/egusphere-egu2020-8270, 2020.

Risk assessment at active volcanic islands link to populated areas is of first importance. We evaluate the potential of satellite imagery to map and monitor the activity of shallow-water hydrothermal systems, which are often found at volcanic islands. For this study, we used publicly available data and proprietary WorldView-2 satellites images, with spectral bands that can penetrate up to water depths of 30 m. Shallow water hydrothermal sites are visible on satellite imagery, primarily with publicly available data, demonstrating the potential of satellite imagery to study and monitor shallow water hydrothermal activity. We focus our work on volcanic islands, showing intense near-shore, shallow-water hydrothermal activity, and distinct styles of hydrothermal venting. Satellite imagery constrains regional outflow geometry and the temporal variability or stability of these systems. Milos Island shows hydrothermal outflow associated with reflective mineral precipitates and/or bacterial mats, which are stable over time (2010-2014). These outflows locally define polygonal patterns likely associated with hydrothermal convection in porous media. In Kueishantao Island individual hydrothermal plumes charged with particles are visible at the sea surface, and display great variability in intensity and distribution of plume sources (2002-2019). Worldwide we have identified ~15 shallow water hydrothermal sites with satellite imagery, that are similar to either the Milos system (e.g., Vulcano and Panarea, Italy), or the Kueishantao system (numerous sites in Pacific volcanic islands). This study demonstrates that satellite imagery can be used to map and monitor different types of shallow-water hydrothermal systems, at regional scale, and monitor their evolution. Satellite data provides not only regional and temporal information on these systems, unavailable to date, but also the regional context for follow-up in situ field data and observations (e.g., instrumental monitoring, sampling, observations and mapping with divers or AUVs) to understand both the nature and dynamics of these systems, and ultimately the associated fluxes.

How to cite: Martelat, J.-E., Escartin, J., and Barreyre, T.: Volcanic submarine hydrothermal activity from satellites : regional mapping and temporal evolution in shallow water systems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9144, https://doi.org/10.5194/egusphere-egu2020-9144, 2020.

Submarine hydrothermal activity is common at the flanks of volcanic islands, and in some cases, occurring at very shallow water (0-100 meter depth). These sites are a key target for systematic seafloor mapping to understand the location, geometry and nature of hydrothermal discharge. These data are also critical for monitoring the temporal variability of these dynamic systems, while providing a context for instrumental measurements, sampling and other observations (e.g., temperature of outflow, chemistry, etc.). Here we present a systematic mapping of the Milos hydrothermal system in the Hellenic volcanic Arc, characterized by submarine gas emissions, high-temperature outflow, bacterial mats, precipitation of hydrothermal minerals, and small hydrothermal constructs and edifices. We have mapped this site at regional scales using satellite imagery (World-View2 images from the DigitalGlobe foundation), complemented with aerial photography acquired with drones, and high-resolution seafloor photomosaics (<1 cm resolution) from underwater imagery acquired by the autonomous underwater vehicle Sparus II (University of Girona). 

Our drone and AUV mapping ground truths the correlation between patterns in satellite imagery and hydrothermal outflow, associated to mineral precipitates and/or bacterial mats at the seafloor. This mapping also reveals a clear organization of the hydrothermal outflow in sandy areas. In particular, polygonal patterns are common and often associated with inactive or actively bubbling pockmarks. These areas, showing white bacterial mats and hydrothermal precipitates, are rippled, suggesting that the hydrothermal precipitates do not consolidate the sediment. White precipitates display subseafloor temperatures >50°C at depths of 10 to 50 cm. The white areas are bound by bands of seafloor with a hummocky structure due to intense bioturbation, that obliterates the ripples, with widths of up to a few meters. This area shows subseafloor temperatures of 20-40°C, and corresponds to a transition from the high-temperature white zones and the seafloor with ripples and no hydrothermal precipitates. This area exhibits subseafloor temperatures similar to those of seawater, and can be associated with seagrass. These patterns reveal a clear organization of a narrowly focused hydrothermal outflow that controls the biological communities at the seafloor and subseafloor. We will discuss the implications of these observations to quantify hydrothermal fluxes in the study area.

How to cite: Puzenat, V., Martelat, J.-E., Escartin, J., Barreyre, T., Gracias, N., Vallicrosa, G., Garcia, R., Magí, L., Nomikou, P., Grandjean, P., Allemand, P., Schouw, A., Le Moine Bauer, S., Jørgensen, S. L., Antoniou, V., Vlasopoulos, O., Polymenakou, P., Mandalakis, M., Coskun, O., and Orsi, W.: Integrated regional scale view of Milos submarine hydrothermalism, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11612, https://doi.org/10.5194/egusphere-egu2020-11612, 2020.

The formation of the oceanic island Surtsey in the shallow ocean off the south coast of Iceland in 1963-1967 remains one of the best-studied examples of basaltic emergent volcanism to date. The island was built by both explosive, phreatomagmatic phases and by effusive activity forming lava shields covering parts of the explosively formed tuff cones.   A detailed gravity survey was carried out on Surtsey in July 2014 with a gravity station spacing of ~100 m.  We analyse these data in order to refine a 2.5D-structural and density model of the internal structure for this type locality of Surtseyan volcanism.  We carry out a complete Bouguer correction of these data using total terrain corrections based on detailed DEMs of the island and the submarine bathymetry.  The principal components of the island are the two tuff cones composed principally of lapilli tuff; this was originally phreatomagmatic tephra formed in the explosive phases of the eruption. Lapilli tuff can be subdivided into (1) submarine lapilli tuff and (2) lapilli tuff above sea level. Other units are (3) subaerial lava, and (4) subaqueous lava deltas. Minor components that are volumetrically insignificant are small intrusions, and unconsolidated and unaltered tephra, still found in thin layers flanking the tuff cones.  An additional formation, relevant for any analysis of the subsurface structure of Surtsey, is (5) the sedimentary rocks making up the seafloor, being at least 100 m thick but probably much thicker.  Using measurements of the density of all the above components, and subdividing the island into different units based on its pattern of growth, we specifically attempt to constrain the width and depth of diatreme structures proposed by Moore (1985) and confirmed in the ICDP SUSTAIN drilling of Surtsey in 2017 (Jackson et al., 2019).  Our forward modeling is aided by a detailed subdivision of the island into units (1) to (4) based on repeated mapping of the island during 1964-1967.

Moore, J. G., 1985, Geological Magazine 122, 649–661

Jackson, M. D., et al. 2019, Scientific Drilling 25, 35–46.

How to cite: Sayyadi, S., T.Gudmundsson, M., Högnadóttir, T., White, J., and D. Jackson, M.: Gravity modeling of the volcanic island of Surtsey, Iceland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13580, https://doi.org/10.5194/egusphere-egu2020-13580, 2020.

Volcanic islands are the sites of some of the largest submarine landslides observed on Earth. Individual landslide deposits can contain several hundreds to few thousands of cubic kilometers of mobilized material and, therefore, represent significant hazards. They can generate destructive tsunamis which may have devastating impacts on coastal areas and populations. Hazard potential of volcanic flank-collapses is widely recognized, but the magnitude, and therefore the hazard potential of tsunamis triggered by such collapses have been much debated over the past decades. Hence, a better understanding and a full characterization of volcanic landslide deposits and emplacement dynamics is crucial. Fogo Island, situated in the southern part of the Cape Verdean Archipelago, is one of the most active oceanic intraplate volcanoes in the world. Fogo Volcano experienced a catastrophic flank-collapse event as witnessed by up-to-1 km high, eastward-opened horseshoe-shape depression. Tsunami deposits found on the nearby islands of Santiago and Maio indicate that the flank-collapse was tsunamigenic (Ramalho et al. 2015; Madeira et al. 2019). To better constrain the tsunamigenic hazard potential of this large, volcanic flank-collapse, we collected in 2019 a dense network of marine geophysical datasets offshore Fogo. Our dataset includes high-resolution multi-beam swath bathymetry, parametric sediment echo-sounder, multi-channel seismic reflection, sidescan sonar data and sediment gravity cores. Here, we present the key results of the seismic data. We show – for the first time – the internal architecture of the Monte Amarelo flank-collapse deposit in unprecedented detail. Our data reveal a two-fold nature of the deposit with hummocky terrains in the proximal area – typical of blocky debris avalanche deposits – and finer-grained, acoustically transparent deposits in the southern distal part. Our observations support recently-proposed failure models, where the loading of seafloor sediment by volcanic debris avalanche deposits triggered sediment destabilization and progressive downslope-propagating failure along a décollement surface (Le Friant et al. 2015, 2020). The basal surface of the Monte Amarelo deposits along with a series of strong internal reflections have also been captured in the seismic data, both in the proximal and distal part. This suggests a multi-phase event in the emplacement of the Monte Amarelo deposit offshore and allows us to reassess the volume of failed and remobilized material. Such details are particularly unusual on submarine volcanic flanks, as it is rather difficult to image the base of debris avalanche deposits due to their hummocky nature that instantly diffract/scatter the acoustic energy. This makes Fogo’s Monte Amarelo volcanic flank-collapse deposit a perfect study case to investigate the emplacement dynamics of large-scale, volcanic flank collapses and better constrain their tsunamigenic hazard potential.

How to cite: Lebas, E., Klein, E., Barrett, R., Ramalho, R., Lindhorst, K., Klaucke, I., Klügel, A., Kutterolf, S., and Krastel, S.: Internal architecture of the two-fold nature Monte Amarelo volcanic flank-collapse deposit offshore Fogo Island in the southern Cape Verdean Archipelago, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19095, https://doi.org/10.5194/egusphere-egu2020-19095, 2020.

Comparison of the results of new investigations of the 1979 and 2017 cored boreholes coupled with observations of the dynamic surface of Surtsey have modified our concepts of the subsurface structure of the volcano, an oceanic island erupted from 1963–1967 on the insular shelf of the south coast of Iceland. The temperature anomalies in the 2017 vertical and inclined boreholes closely resembled each other in shape and magnitude even though they are 80 m apart horizontally. The peak temperature of the vertical hole anomaly immediately after drilling was 124 °C at 105 m below surface (m.b.s.) and the inclined hole anomaly 127 °C at 115 m.b.s. This temperature anomaly and the paucity of coherent basalt in the 2017 cores casts doubt on a previous concept — that the heat anomaly in the 1979 borehole, 141 °C at 100–106 m.b.s., was due to nearby intrusions. The new observations suggest instead that top-down heating from the subaerial lava shield may have contributed to the Surtsey thermal anomaly.  In August 1966–June 1967, lava flows rapidly filled the Surtur vent crater to 80 m.b.s. and overflowed to the south and east. The conduction of heat from the cooling shield into the water-saturated substrate would have been influenced by the material characteristics of the underlying lapilli tuff, but the mechanisms of downwards heat transfer are not clear. In the zone of tidal flux centred at ~58 m.b.s., for example, the tuff was highly porous in 1979 and it remains porous and permeable 50 years after eruptions terminated. Boiling of interstitial water below sea level could have produced steam that rose and warmed the porous and permeable tephra adjacent to the lava shield, where it produced broad areas of palagonitized tuff.  Other sources of heat are also under consideration. At 107 m.b.s., fresh glass in the lapilli tuff of the original 1979 thin sections contains abundant granular and microtubular structures. These resemble endolithic microborings, and they are perhaps indicative of an early, short-lived episode of cooler temperatures and functional microbial activity at <120 °C. A geometrical analysis of layering in unrolled digital scans of the 2017 cores indicates that the relation of the apparent dip to the true dip of layering in the core inclined 55° from horizontal is such that steep dips are more common in westerly true dips, and gentle dips are more common in easterly true dips. The measurements indicate that near-surface layering in both the vertical and inclined cores dips westerly, suggesting that the boreholes are located inside the Surtur crater.  In this proximal setting, the section of lapilli tuff may be almost entirely composed of facies re-sedimented from unstable depositional sites and/or recycled through the vent perhaps multiple times. Sub-seafloor lapilli tuff samples with high porosity, high water absorption and low unit weight may reflect these complex eruptive processes. The new observations support the hypothesis that broad conduit and vent filling deposits underlie the Surtur crater.

How to cite: Moore, J. G. and Jackson, M. D.: Observations on the Structure of Surtsey, Iceland, and its Basaltic Lapilli Tuff, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21018, https://doi.org/10.5194/egusphere-egu2020-21018, 2020.

Surface reaction kinetics of volcanic materials at hydrothermal conditions – an in-situ experiment at the Surtsey volcano

The diversity and functioning of microbial life is a key research topic in the field of marine geochemistry and geobiology. For understanding biological processes at the temperature limit of functional life, it is necessary to gain insights about microbe-rock-fluid interactions under natural hydrothermal conditions within the basaltic ocean crust. Although there has been research in the field of biological interactions on olivine and tephra surface in laboratories and samples from volcanos ([1], [2]), the kinetics of microbe-rock-fluid interactions has not been systematically evaluated by in-situ experiment in a natural reservoir.

During the ICDP SUSTAIN Expedition 5059 at the Surtsey volcano off the southern coast of Iceland in 2017, a borehole was endowed with a subsurface observatory to analyze the evolution of olivine (Fo₉₀) and volcanic glass surfaces embedded in PEEK containers at fixed temperatures ranging from 25°C to 125°C for two years ([3]). This incubation experiment delivers novel data of surface reaction kinetics under defined conditions in a natural setting.

In-depth analysis of the sample surface with vertical scanning interferometry, atomic force microscopy as well as Raman spectrometry provides insights into solid-fluid reactions of volcanic minerals. On the one hand, this analysis delivers a quantitative and qualitative breakdown of the chemical and physical alteration of natural matter below the oceanic crust. On the other hand, the in situ experiment facilitates a validation of a range of experiments that have been performed in laboratories under similar conditions. The possibility to gain knowledge about dissolution and precipitation on the interface of common seafloor materials within a natural hydrothermal system is critical step towards understanding submarine microbial life.

[1] Konhauser, K. O., Schiffman, P., and Fisher, Q. J., Microbial mediation of authigenic clays during hydrothermal alteration of basaltic tephra, Kilauea Volcano, Geochem. Geophys. Geosyst., 3( 12), 1075, doi:10.1029/2002GC000317, 2002.

[2] Malvoisin, B., Brunet, F., Carlut, J., Rouméjon, S., and Cannat, M. (2012), Serpentinization of oceanic peridotites: 2. Kinetics and processes of San Carlos olivine hydrothermal alteration, J. Geophys. Res., 117, B04102, doi:10.1029/2011JB008842.

[3] Türke, A., et al. (2019). "Design of the subsurface observatory at Surtsey volcano, Iceland." Sci. Dril. 25: 57-62.

How to cite: Peter, M., Bach, W., Kahl, W.-A., Luttge, A., Turke, A., and Jorgensen, S. L.: Surface reaction kinetics of volcanic materials at hydrothermal conditions – an in-situ experiment at the Surtsey volcano, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21685, https://doi.org/10.5194/egusphere-egu2020-21685, 2020.

The volcanic system of Ischia is characterized by an intense hydrothermal activity, documented since the early 16th century by the study of Iasolino (1588), which represents the first systematic analysis of the thermal springs of the island for therapeutic purposes. Later studies partially contributed to the enhancement of knowledge on the volcanic, hydrogeological and hydrothermal features of the island, highlighting the strong interaction between hydrothermal flowpaths and volcano-tectonic processes . The reconstruction of the hydrothermal system becomes, therefore, a fundamental element for territorial planning, not only in terms of management of the huge water and geothermal resource, but also and above all in a perspective of prevention and mitigation of volcanic risk. Thermal springs, fumaroles and clay deposits due to the hydrothermal alteration of volcanic products testifies for the existence of an active deep hydrothermal system. Commonly, the geochemical characterization of fluids and groundwater has been used for the definition of the origin and structure of hydrothermal systems, when hydrogeological information is incomplete. However, volcanic hydrothermal systems, such as that characterizes the island of Ischia, are particularly difficult to analyze and outline, as the groundwater resources are the result of an articulated and dynamic interaction among meteoric water, sea water and fluids of deep origin. In such cases, the need for an interdisciplinary approach is evident, involving knowledge and research methods ranging from geology to volcanology, geophysics, geochemistry and hydrogeology. With particular reference to the functional and structural representation of the geothermal system of the island of Ischia and the resulting correlations with the volcano-tectonic processes, the examination of previous information highlights the need to update and improve the knowledge on groundwater hydrodynamics and mineralization processes.

Therefore, this study represents the result of  a strong interdisciplinary action that, starting from the design and implementation of a database on the existing geological/volcanological and hydrogeological information, contributes to highlight the critical issues, defines an operating scheme of the hydro-geo-thermal system of the island of Ischia, and aims at upgrade its hydrogeological, geochemical and volcanic monitoring system, in order to contribute to the mitigation of natural risks.

Moreover, this study well fits into the framework of the ongoing researches on volcanic hazard at Ischia and is integrated with the actions planned by the Italian Department of Civil Defense. The knowledge of groundwater dynamics and pathways is of fundamental importance for understanding the water/magma interaction processes in case of re-alimentation of the shallow magmatic system, and the assessment of the possibility of phreatic explosions occurrence.

How to cite: de Vita, S., Di Vito, M. A., Marotta, E., Avino, R., Carandente, A., Belviso, P., Fabbrocino, S., Giardino, A., Marino, L., and Todisco, F.: Groundwater flow and fluid/groundwater geochemical characterization at Ischia Island: a new strategy for the mitigation of the volcanic risk, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22083, https://doi.org/10.5194/egusphere-egu2020-22083, 2020.