Flank Of Volcano Research Articles

Helium-carbon systematics of groundwaters in the Lassen Peak Region

Carbon dioxide emissions from active subaerial volcanoes represent 20–50% of the annual global volcanic CO2 flux (Barry et al., 2014). Passive degassing of carbon from the flanks of volcanoes, and the associated accumulation of dissolved inorganic carbon (DIC) within nearby groundwater, also represents a potentially important, yet poorly constrained flux of carbon to the surface (Werner et al., 2019). Here we investigate sources and sinks of DIC in groundwaters in the Lassen Peak region of California. Specifically, we report and interpret the relative abundance and isotopic composition of helium (3He, 4He) and carbon (12C, 13C, 14C) in 37 groundwater samples, from 24 distinct wells, collected between 20 and 60 km from Lassen Peak. Measured groundwater samples have air-corrected 3He/4He values between 0.19 and 7.44 RA (where RA = air 3He/4He = 1.39 × 10−6), all in excess of the radiogenic production value (~0.05 RA), indicating pervasive mantle-derived helium additions to the groundwater system in the Lassen Peak region. Stable carbon isotope ratios of DIC (δ13C) vary between −12.6 and − 27.7‰ (vs. VPDB). Measured groundwater DIC/3He values fall in the range of 2.2 × 1010 to 1.1 × 1012. Using helium and carbon isotope data, we explore several conceptual models to estimate surface carbon contributions and to differentiate between DIC derived from soil CO2 versus DIC derived from external (slab and mantle) carbon sources. Specifically, if we use 14C to identify soil-derived DIC (assuming decadal-to-centennial groundwater ages and a soil CO214C activity equal to that of the atmosphere), we calculate that a hypothetical external carbon source would have an apparent δ13C signature between −10.3 and − 59.3‰ (vs. Vienna Pee Dee Belemnite (VPDB)) and an apparent C/3He between 7.0 × 109 and 1.0 × 1012. These apparent δ13C and C/3He values are substantially isotopically lighter than and greater than canonical MORB values, respectively. We suggest that >95% of any external (non-soil-derived) DIC in groundwater must thus be non-mantle in origin (i.e., slab derived or assimilated organic carbon). We further investigate possible sources of external DIC to groundwater using two idealized conceptual approaches: a pure (unfractionated) source mixing model (after Sano and Marty, 1995) and a scenario that invokes fractionation due to calcite precipitation. Because the former model requires carbon contributions from an organic source component with unrealistically low δ13C (~ − 60‰), we suggest that the second scenario is more plausible. Importantly, however, we caution that all conceptual models are dependent on assumptions about initial 14C activity. Thus, we cannot rule out the possibility that the true fraction of non-surface-derived DIC in these samples is lower or negligible, despite the pervasive mantle-derived He isotope signatures throughout the region. Following the 14C approach to deconvolving sources of DIC, we determine that the maximum passive carbon flux could be up to ~2.2 × 106 kg/yr, which is lower than previous magmatic carbon flux estimates from the Lassen region (Rose and Davisson, 1996). We find that the passive dissolved carbon flux could represent a maximum of ~4–18% of the total Lassen geothermal CO2 degassing flux (estimated to be ~3.5 × 107 kg/yr Rose and Davisson, 1996; Gerlach et al., 2008), which is still more than an order of magnitude smaller than soil gas CO2 flux estimates (7.3–11 × 107 kg/yr) for nearby volcanoes (Sorey et al., 1998; Gerlach et al., 1999; Evans et al., 2002; Werner et al., 2014). We conclude that passive dissolved carbon fluxes should be combined with geothermal fluxes and soil gas fluxes to obtain a complete picture of volcanic carbon emissions globally. Our approach highlights the utility of measuring helium isotopes in concert with the full suite of noble gas abundances, tritium, δ13C and 14C, which when interpreted together can be used to better elucidate the various sources of DIC in groundwater.

Exploring the links between volcano flank collapse and the magmatic evolution of an ocean island volcano: Fogo, Cape Verde

Mass-wasting of ocean island volcanoes is a well-documented phenomenon. Massive flank collapses may imply tens to hundreds of km3 and generate mega-tsunamis. However, the causal links between this large-scale, low-frequency instability, and the time–space evolution of magma storage, crystal fractionation/accumulation, lithospheric assimilation, and partial melting remains unclear. This paper aims at tracking time variations and links between lithospheric, crustal and surface processes before and after a major flank collapse (Monte Amarelo collapse ca. 70 ka) of Fogo volcano, Cape Verde Islands, by analysing the chemical composition (major, trace elements, and Sr–Nd–Pb isotopes) and age-controlled stratigraphy (K–Ar and Ar–Ar dating) of lavas along vertical sections (Bordeira caldera walls). The high-resolution sampling allows detecting original variations of composition at different time-scales: (1) a 60 kyrs-long period of increase of magma differentiation before the collapse; (2) a 10 kyrs-long episode of reorganization of magma storage and evacuation of residual magmas (enriched in incompatible elements) after the collapse; and (3) a delayed impact at the lithospheric scale ~ 50 kyrs after the collapse (increasing EM1-like materiel assimilation).

Gas Geochemistry at Grande Comore and Mayotte Volcanic Islands (Comoros Archipelago), Indian Ocean

AbstractThe Comoros archipelago is an active geodynamic region of intra‐plate volcanism within which the youngest and oldest islands (Grande Comore and Mayotte respectively) are characterized by recent volcanic activity. The frequent eruptions of the large shield volcano Karthala on Grande Comore (last eruption 2007), and the recent birth of a large submarine volcano since 2018 at the submarine base of Mayotte are associated with permanent fumarolic emissions, bubbling gas seeps, and soil gas emissions, which are studied in detail here for the first time. CO2 fluxes and chemical and isotopic gas compositions acquired during two surveys in 2017 and 2020 are integrated with older data sets collected between 2005 and 2016, permitting the identification of a possible influence of the recent volcanic and magmatic activity at Mayotte. At Karthala, high gas fluxes with high temperature, and a marked magmatic signature are concentrated close to the summit crater area, while only weaker emissions with a stronger biogenic signature are found on the volcano flanks. At Mayotte, lower temperature and higher CH4 content are recorded in two main seep areas of CO2‐rich fluid bubbling, while soil emissions on land record a higher proportion of magmatic fluids compared to Karthala. Our preliminary results reveal two quite separate gas emission patterns for each island that are distinct in composition and isotopic signatures, and well correlated with the present state of volcanic activity. This work may potentially provide support for local observation infrastructures and contribute to the improvement in volcanic and environmental monitoring.

Stable isotope and anthropogenic tracer signature of waters in an Andean geothermal system

In the present study, we combined stable isotopes and anthropogenic tracers to investigate the origin, residence times, and evolution of thermal waters in the Lonquimay-Tolhuaca Volcanic Complex (LTVC) of the southern Chilean Andes. A total of 20 water samples from springs discharging at a broad range of temperatures (8–96 °C) were collected and analyzed for major ion geochemistry, stable isotope ratios (δ2H, δ18O, δ13CTDIC), dissolved chlorofluorocarbons (CFCs) and sulfur hexafluoride (SF6). In addition, we compiled all available data on the isotopic composition of precipitation in the region to derive the local meteoric water line. Coupled with a Rayleigh-fractionation model of precipitation, we provide constraints on the elevation at which infiltration and recharge to the system is produced. δ13CTDIC values are consistent with the bulk of dissolved inorganic carbon being derived from the addition of soil CO2 to an atmospheric source, while magma degassing and boiling processes are evidenced in samples discharging directly on the flanks of volcanoes. The isotopic composition of thermal water, once heated at depth, is further modified by CO2 degassing and carbonate precipitation during ascent. All geothermal samples contain low but detectable concentrations of CFC-11, CFC-12, CFC-113, and SF6, suggesting the addition of only a small fraction (2–22%) of modern meteoric water. The discharge temperature of naturally outflowing springs in the LTVC correlates directly with the age distribution of the water samples. This difference in residence times is attributed to the distinct subsurface circulation pathways of each water type—i.e., the shallow, diffuse flow of cold groundwater vs. the deep, focused circulation of thermal water along fault zones. Conduit flow along high vertical permeability networks allows hydrothermal fluid to remain relatively unmixed with shallow meteoric water during ascent. Data from this study confirm that fault-fracture meshes with different orientations exert a first order control on the residence times, ascent, and mixing rates of thermal waters in this segment of the Andean Cordillera, thus modulating their chemical and isotopic signature. Additionally, our results show that the combined use of conventional hydrogeochemical and isotopic data with environmental tracers, including anthropogenic CFCs and SF6, is a powerful tool to better understand the dynamics of geothermal systems.

Precipitation‐Driven Pedogenic Weathering of Volcaniclastics on Early Mars

AbstractCompositional stratigraphy, generally composed of Al‐rich clay minerals overlying Fe/Mg‐rich clay minerals, is observed in many locations on Mars. Here we describe the occurrence of such mineralogical stratigraphy in settings where the protoliths are almost certainly pyroclastic materials. One such example includes altered rocks high on the summit and flanks of explosive volcanoes in Thaumasia Planum. These clay‐bearing deposits are most consistent with precipitation‐driven weathering of ash deposits. Considering explosive volcanism was pervasive in the Noachian, the early sedimentary record of Mars in some locations is likely dominated by glassy, fragmented, porous, chemically reactive materials with highly specific surface area. These pyroclastic deposits were potentially a critical geological component linking clay minerals to elements of Mars’ climate, weathering, and sedimentary puzzle.

Correction to: Tsunamis from prospected mass failure on the Marsili submarine volcano flanks and hints for tsunami hazard evaluation

Correction to: Tsunamis from prospected mass failure on the Marsili submarine volcano flanks and hints for tsunami hazard evaluation

Modelling future lahars controlled by different volcanic eruption scenarios at Cotopaxi (Ecuador) calibrated with the massively destructive 1877 lahar

AbstractLahars are among the most hazardous mass flow processes on earth and have caused up to 23 000 casualties in single events in the recent past. The Cotopaxi volcano, 60 km southeast of Quito, has a well‐documented history of massively destructive lahars and is a hotspot for future lahars due to (i) its ~10 km2 glacier cap, (ii) its 117–147‐year return period of (Sub)‐Plinian eruptions, and (iii) the densely populated potential inundation zones (300 000 inhabitants). Previous mechanical lahar models often do not (i) capture the steep initial lahar trajectory, (ii) reproduce multiple flow paths including bifurcation and confluence, and (iii) generate appropriate key parameters like flow speed and pressure at the base as a measure of erosion capacity. Here, we back‐calculate the well‐documented 1877 lahar using the RAMMS debris flow model with an implemented entrainment algorithm, covering the entire lahar path from the volcano edifice to an extent of ~70 km from the source. To evaluate the sensitivity and to constrain the model input range, we systematically explore input parameter values, especially the Voellmy–Salm friction coefficients μ and ξ. Objective selection of the most likely parameter combinations enables a realistic and robust lahar hazard representation. Detailed historic records for flow height, flow velocity, peak discharge, travel time and inundation limits match best with a very low Coulomb‐type friction μ (0.0025–0.005) and a high turbulent friction ξ (1000–1400 m/s2). Finally, we apply the calibrated model to future eruption scenarios (Volcanic Explosivity Index = 2–3, 3–4, >4) at Cotopaxi and accordingly scaled lahars. For the first time, we anticipate a potential volume growth of 50–400% due to lahar erosivity on steep volcano flanks. Here we develop a generic Voellmy–Salm approach across different scales of high‐magnitude lahars and show how it can be used to anticipate future syneruptive lahars.

Chapter 7.4 Active volcanoes in Marie Byrd Land

Abstract Two volcanoes in Marie Byrd Land, Mount Berlin and Mount Takahe, can be considered active, and a third, Mount Waesche, may be as well; although the chronology of activity is less well constrained. The records of explosive activity of these three volcanoes is well represented through deposits on the volcano flanks and tephra layers found in blue ice areas, as well as by the presence of cryptotephra layers found in West and East Antarctic ice cores. Records of effusive volcanism are found on the volcano flanks but some deposits may be obscured by pervasive glacerization of the edifices. Based on a compilation of tephra depths–ages in ice cores, the activity patterns of Mount Takahe and Mount Berlin are dramatically different. Mount Takahe has erupted infrequently over the past 100 kyr. Mount Berlin, by contrast, has erupted episodically during this time interval, with the number of eruptions being dramatically higher in the time interval between c. 32 and 18 ka. Integration of the Mount Berlin tephra record from ice cores and blue ice areas over a 500 kyr time span reveals a pattern of geochemical evolution related to small batches of partial melt being progressively removed from a single source underlying Mount Berlin.

Непрерывный мультиспутниковый мониторинг вулканов для обнаружения извержений на примере бокового прорыва вулкана Ключевской в феврале 2021 г.

Непрерывный мультиспутниковый мониторинг вулканов для обнаружения извержений на примере бокового прорыва вулкана Ключевской в феврале 2021 г.

Tsunamis from prospected mass failure on the Marsili submarine volcano flanks and hints for tsunami hazard evaluation

The Marsili Seamount (Tyrrhenian Sea, Italy) is the largest submarine volcano in the Mediterranean Sea, located in the middle of the Marsili Basin, facing the Calabrian and Sicilian coasts on its eastern side, and the coasts of Sardinia on the opposite side. It has erupted in historical times, and its summit crest is affected by widespread hydrothermal activity. This study looks at mass failures taking place at different depths on the flanks of the volcano and estimates their associated tsunamigenic potential. Mass failure, tsunami generation, and propagation have been simulated by means of numerical models developed by the Tsunami Research Team of the University of Bologna. In all, we consider five cases. Of these, three scenarios, one regarding a very small detachment and two medium-sized ones (between 2 and 3 km3 failure volume), have been suggested as possible failure occurrences in the published literature on a morphological basis and involve the north-eastern and north-western sectors of the volcano. The two additional cases, one medium-sized and one extreme, intended as a possible worst-case scenario (volume 17.6 km3), affecting the eastern flank. Results indicate that small-volume failures are not able to produce significant tsunamis; medium-size failures can produce tsunamis which dangerously affect the coasts if their detachment occurs in shallow water, i.e., involves the volcano crest; and extreme volume failures have the potential to create disastrous tsunamis. In all the simulations, tsunami waves appear to reach the Aeolian Islands in around 10 min and the coasts of Calabria and Sicily in 20 min. This study highlights that there is a potential for dangerous tsunamis generation from collapses of the Marsili volcano and as a consequence a need to intensify research on its status and stability conditions. More broadly, this investigation should also be extended to the other volcanic seamounts of the Tyrrhenian Sea, since their eruptive style, evolution, and tsunamigenic potential are still poorly known.

Rapid magmatic processes drive persistently active volcanism

Rapid transitions between long periods of relatively benign low magnitude activity and short episodes of higher magnitude eruption, pose significant risk to local populations. Here we investigate the relationship between persistent, low magnitude activity and upsurges to more sever eruptions at four persistently to intermittently active volcanoes in the Vanuatu Arc (Yasur, Ambrym, Ambae and Lopevi) using uranium-series isotopes. This approach offers the unique ability to examine both magmatic processes and the timescales over which they operate. Significant 226Ra excesses at Ambrym, Ambae and Lopevi, as high as 6.56, indicate fast transit of magma through the crust, suggesting that persistent activity is driven by continuous magma supply. At Yasur, equilibrium between 210Pb and 226Ra in erupted magmas reveals rapid magma replenishment and degassing. Rapid ascent is facilitated by crustal weakness that favours the formation of open conduits, either as a result of regional tectonic regimes or localised caldera formation. At Yasur (230Th/232Th) in lavas and tephras varies between 1.449 and 1.482 and (226Ra/230Th) ranges between 1.165 and 2.069, while at Ambrym (226Ra/230Th) extends from 2.796 to 6.557. This observed variation in ThRa isotopes cannot be explained by simple models of magma replenishment and mixing, and instead requires cryptic assimilation with older, stored crystal mushes. Evidence for this cryptic assimilation differs between the examined volcanoes, suggesting differences in the location of mush zones. At Ambrym, Ambae and Lopevi the tectonic regime favours rifting, and mushes accumulate in the volcano's flanks, while at Yasur a ‘typical’ subduction regime leads to development of a large crystal mush body directly beneath the volcano. These differences in mush storage have significant impact on the frequency and magnitude of upsurges in eruption intensity at these volcanoes, with mush bodies stored beneath the volcano remobilised to produce lower frequency/higher magnitude eruptions.

Editorial: Flank dynamics, sector collapses, lahars, and rockfalls: analysis, monitoring, and modelling of small to large scale volcanic slope instability

Slope dynamics in volcanic environments comprise a wide spectrum of phenomena, from large lateral collapse to shallow debris remobilization, which may represent a major threat for human communities and infrastructures. Many volcanos built up from the ocean floor and large portions of the volcano edifice are submerged. In these settings, only the edifice’s summit can be investigated by terrestrial remote sensing and in-situ approaches. Growth and destruction, including tectonics and gravitational phenomena, affect entire volcano flanks and are not limited to the physical boundary of the sea level but could comprise their subaqueous parts

Overflows and Pyroclastic Density Currents in March-April 2020 at Stromboli Volcano Detected by Remote Sensing and Seismic Monitoring Data

Between 28 March and 1 April 2020, Stromboli volcano erupted, with overflows from the NE crater rim spreading along the barren Sciara del Fuoco slope and reaching the sea along the NW coast of the island. Poor weather conditions did not allow a detailed observation of the crater zone through the cameras monitoring network, but a clear view of the lower slope and the flows expanding in the area allowed us to characterize the flow features. This evidence was integrated with satellite, GBInSAR, and seismic data, thus enabling a reconstruction of the whole volcanic event, which involved several small collapses of the summit cone and the generation of pyroclastic density currents (PDCs) spreading along the slope and on the sea surface. Satellite monitoring allowed for the mapping of the lava flow field and the quantification of the erupted volume, and GBInSAR continuous measurements detected the crater widening and the deflation of the summit cone caused by the last overflow. The characterization of the seismicity made it possible to identify the signals that are associated with the propagation of PDCs along the volcano flank and, for the first time, to recognize the signal that is produced by the impact of the PDCs on the coast.

Potential mass movements on the Palinuro volcanic chain (southern Tyrrhenian Sea, Italy) and consequent tsunami generation

The Palinuro volcanic chain (PVC) is located about 80 km offshore the Campania region (Italy) in the southern sector of the Tyrrhenian Sea. The chain consists of 15 volcanic edifices aligned in an E-W direction with two distinct major seamounts (Palinuro and Glabro). They cover a 90 km long and 20 km wide area, with a present-day volume of 2700 km3. Palinuro volcanism emplaced between 0.8 and 0.3 Ma, although shallow seismicity and hydrothermalism indicate an ongoing volcanic activity. A geomorphological analysis of the volcanic chain and data from a multichannel seismic profile reveal large volumes of buried chaotic material suggesting gravity mass sliding from the volcano flanks and slide scars. A stability analysis of the Palinuro flanks has been carried out to determine the sectors potentially prone to sliding in case of shallow volcanic earthquakes. Landslides are simulated by adopting a scenario-based approach. Tsunamis induced by these mass movements and their propagation across the Tyrrhenian Sea are modeled. Results suggest that shallow earthquakes (M ~4.6–4.8) are able to destabilize the flanks of the volcanic chain generating slope failures. Sliding volumes in the order of 1.5 km3 and 2.4 km3 may induce waves as high as 1.5 and 6 m, respectively, along the peri-Tyrrhenian coast. Our results underline the need for further investigations on the stability of the submarine volcanoes of the Tyrrhenian basin. These volcanoes are still poorly known although their instability could trigger large tsunamis along the southern Italy coastal sectors. Our recommendation is that multiparamertic monitoring networks on PVC and periodic oceanic cruises should be put into action, and further that a systematic evaluation of the tsunami hazard related to possible sliding phenomena on the flanks of the Tyrrhenian seamounts should be performed.

Preferably Plinian and Pumaceous: Implications of Microbial Activity in Modern Volcanic Deposits at Askja Volcano, Iceland, and Relevancy for Mars Exploration

To search more efficiently for a record of past life on Mars, it is critical to know where to look and thus maximize the likelihood of success. Large-scale site selection for the Mars 2020 mission has been completed, but small (meter to 10 cm)-scale relationships of microenvironments will not be known until the rover reaches the surface. Over a 2 m transect at a modern volcanic deposit on the flank of Askja volcano in the barren highlands of Iceland, we compared two biological indicators (ATP activity and 16SrRNA amplicon sequence composition) to physical characteristics including bulk chemical composition, spectral signatures of mineralogy, and grain size. Using analytical instrumentation analogous to those available on Mars rovers, we were able to characterize the geological setting of the deposits and link physical parameters to microbial abundance and diversity. In general, methanogenesis, methanotrophy/methylotrophy, and nitrate reduction were the functional traits most associated with microbial community shift along the transect. Core microbiome members tended to be associated with nitrate reduction, and relative abundance of core microbes was strongly related to free water in the deposit. Community compositional shift of the rare microbiome was related to microenvironmental changes such as change in grain size, geochemistry, and age of deposit. These correlations lead us to suggest a sampling strategy that accounts for Martian geology, looking for undisturbed (not remobilized) explosive volcanic ash below pumice that could maximize diversity and abundance of different bioindicators. Our study also illustrates the importance of studying the variability across microenvironments in low biomass settings on earth.

Alluvial fans on volcanic islands: A morphometric perspective (São Vicente, Cape Verde)

The distribution, morphology and development of volcanic island alluvial fans are investigated using São Vicente from the Cape Verde volcanic chain (east-central Atlantic Ocean). This is a tectonically and volcanically inactive dryland setting, comprising an eroded Plio-Pleistocene composite volcano overlying a submarine shield volcano. We mapped 228 alluvial fans, quantifying fan (F) and catchment (C) morphological properties (area [A], gradient [G], relief [R], length [L]). Fans and catchments of varying size and gradient are distributed around the island coastal margins (6%) and along interior valley sides (94%). Regression results (i.e. +ve/−ve slopes of best fit lines) conformed to broader fan research but with weak correlations, and coefficient-exponent values outside, or at the lower end of values reported from non-volcanic settings. Analysis of fan area and gradient vs catchment area regression residuals revealed fans were dominated by small-steep gradient (28%) and large-low gradient forms (39%). Fan building space is a fundamental control, specifically linked to volcano structure, but with interplay between rock strength, base level, and climate. Fans around the volcanic edifice flanks are uncommon due to steep flank slopes. Where flank margin fans occur they are typically small and steep forms due to marine erosion. Fans along flank incised valleys are common. Large low gradient fans are associated with a major volcanic rift-aligned valley structure, with extensive erosion into altered and weathered edifice-core lithologies. Small-steep gradient fans are associated with edifice flank valleys. Steeper and narrower valley forms reflect incision into stronger lithologies of the composite volcano flanks, restricting fan building space. Fans located within the volcano central depression are amongst the largest and lowest gradient types, building into the eroded and unconfined edifice core space. Coalescence, apex-toe incision, toe erosion and catchment stream channel backfilling displayed by most fans suggest landscape erosion dominates during more arid periods (e.g. interglacials), with the dryland setting generating limited sediment and insufficient flood runoff for transport and fan deposition. Fan building likely occurs during wetter periods linked to Quaternary climate variability. Quaternary eustatic variations are relevant for the volcano edifice margins where sea level changes control fan building space and erosion.

Eruptive history and volcano-tectonic evolution of Paka volcanic complex in the northern Kenya rift: Insights into the geothermal heat source

In this paper, we provide insights into the eruptive history and volcano-tectonic evolution of the Paka volcanic complex in a revised stratigraphic framework. We integrate all available 40Ar/39Ar radiometric dates along with field observations, remote sensing data, and the analysis of surface and cutting samples from a 2552 m deep borehole (PK-01). Chemical analyses distinguish basalt, hawaiite, mugearite, benmorite, and trachyte rock type in Paka. It also indicates that the eruptive products are genetically related by fractional crystallization. Major element mass balance and Rhyolite-MELTS models are consistent with the trachyte being generated by 74–83% fractional crystallization of Paka basalt. Before the growth of the volcano, volcanic activity was characterised by plateau fissure eruptions at 582–405 ka. Eruptions directly related to the Paka edifice are divided into four different volcanic sequences. Sequences 1–4 span the periods 390–278 ka, 247–205 ka, 160–36 ka, and 36–8 ka. The Pre-Paka plateau eruption products outcrop at the base of the volcano flanks and are overlain by edifice-forming trachyte. Initial caldera-related subsidence is expressed by arcuate structures to the west and southeast parts of the volcano. These initial collapses are associated with tuff and pyroclastic eruptions estimated to have occurred at ~38 ka. Following these explosive eruptions, a ~1.5 by ~1.6 km main caldera developed. The lithological information from the drilled geothermal exploration borehole PK-01 indicates a minimum thickness of ~2200 m for the extrusive lava sequences, with the uppermost 1050 m of the strata being directly related to eruptions from the Paka volcano (Phases 1–4). We estimate a minimum total bulk volume of ~50 km3 for the volcanic material erupted from Paka during the last ~390 ka. This translates to an average eruption rate of ~1.2 × 10−4 km3/yr. The associated advected magmatic heat supported an ‘excess’ heat flux ranging between 110 and 138 mW/m2 or about twice present day average continental flux (57 mW/m2) and about 1.3 times the background values in geothermal areas (90 mW/m2). The apparent high heat flux implies a magma-driven geothermal system, where convection of the hydrothermal fluid is occurring above the heat source. Structural mapping revealed normal faults, strike-slip faults, lineaments, and an array of eruptive vents and domes as the main volcano-tectonic structures. We infer at least four faulting and fault reactivation events that have occurred during Paka geological history. The structural orientations in the area are dominated by NNE and NW with subordinate N-S and NNW striking structures. Evidence suggests that the intersection of NNE and NW trending structures may have had a major influence on the volcanism in the area.

The evolution of Santa Maria Island in the context of the Azores Triple Junction

Santa Maria is the oldest island in the Azores, formerly belonging to the Eurasia plate and currently the only one sitting on the Nubia Plate, thus sharing a geodynamic evolution with the Azores Triple Junction. It is therefore important to evaluate the effects of active tectonics on the evolution of Santa Maria, for example on its vertical movements. We present new stratigraphic, geomorphologic, structural and geochronological data from Santa Maria which shed further light on how a volcanic ocean island evolves in a tectonically active setting. Santa Maria island started with a first shield volcano (Old Volcanic Complex) that emerged ca. 6.0 Ma ago and was active until ca. 5.3 Ma. The short time span between the first and second shield volcanoes (ca. 0.3 Ma) and the preservation of only the western flank of this first shield volcano indicate an initial flank collapse at ca. 5 Ma. The collapse scar was covered by an eastwards dipping sedimentary complex (Intermediate Sedimentary Complex), with a likely tsunami deposit at the base. A second shield volcano (Young Volcanic Complex) rapidly grew on these sediments from 4.8 to 3.8 Ma, and the island subsided by more than 100 m. At 3.7 Ma, a second flank collapse occurred, as inferred from the missing summit and eastern flank. Volcanism then resumed (3.6 to 2.8 Ma), giving rise to Strombolian cones lying unconformably on the collapse scar and conformable parasitic cones on the unaffected flank. Submarine lavas occurring at up to 200 m altitude with a youngest age of 3.0 Ma indicate major uplift of the island since, at most, that time. Here we interpret uplift as the result of rift flank uplift on the southern shoulder of the nearby Terceira Rift in the last ca. 1.5 Ma.

Modelling 2018 Anak Krakatoa Flank Collapse and Tsunami: Effect of Landslide Failure Mechanism and Dynamics on Tsunami Generation

The 2018 Anak Krakatoa volcano flank collapse generated a tsunami that impacted the Sunda Strait coastlines. In the absence of a tsunami early warning system, it caused several hundred fatalities. There are ongoing discussions to understand how the failure mechanism of this event affected landslide dynamics and tsunami generation. In this paper, the sensitivity to different failure scenarios on the tsunami generation is investigated through numerical modelling. To this end, the rate of mass release, the landslide volume, the material yield strength, and orientation of the landslide failure plane are varied to shed light on the failure mechanism, landslide evolution, and tsunami generation. We model the landslide dynamics using the depth-averaged viscoplastic flow model BingClaw, coupled with depth-averaged long wave and shallow water type models to simulated tsunami propagation. We are able to match fairly well the observed tsunami surface elevation amplitudes and inundation heights in selected area with the numerical simulations. However, as observed by other authors, discrepancies in simulated and observed arrival times for some of the offshore gauges are found, which raises questions related to the accuracy of the available bathymetry. For this purpose, further sensitivity studies changing the bathymetric depth near the source area are carried out. With this alteration we are also able to match better the arrival times of the waves.

Bedforms on the submarine flanks of insular volcanoes: New insights gained from high resolution seafloor surveys

AbstractA comparative analysis of bedform fields along the submarine flanks of insular volcanoes, characterized by different morpho‐structural settings, volcanic and meteo‐marine regimes (Vanuatu, Kermadec, Bismark, Madeira and Aeolian archipelagos), is presented here to provide insights on the size distribution, morpho‐dynamic and genesis of such bedforms. Two main types of bedforms are recognized according to their size, location and preconditioning/triggering processes. Small‐scale bedforms have wavelengths of tens to hundreds of metres and wave heights of metres. Because of their small‐size, they are typically not recognizable at water depths greater than 400 m from vessel‐mounted bathymetric surveys. Few examples of small‐scale bedforms are reported from upper volcanic flanks, where steep gradients commonly hinder their formation. Their recognition is mostly limited to the thalweg of shallow and flat‐bottomed channels that carve the insular shelf on slope gradients <15°. Small‐scale bedforms are mostly related to erosional–depositional processes due to sedimentary gravity flows that are often the result of a cascading effect between volcanic and non‐volcanic processes (for example, flood discharges and retrogressive landslides). Large‐scale bedforms occur at all water depths, having wavelengths of hundreds/thousands of metres and wave heights up to few hundreds of metres. The origin of large bedforms is more difficult to ascertain, especially if only bathymetric data are available. Some diagnostic criteria are presented to distinguish between bedforms associated with landslide deposits and those associated with density currents. In this latter case, relevant sediment sources and slope gradients (<8°) are key factors for bedform development. Erosional–depositional bedforms are typically related to eruption‐fed density flows formed during large caldera collapses or to large turbidity flows. Bedforms generated by turbidity flows are often observed in the lower volcanic flanks, where an abrupt decrease of gradients is present, often matching a change from confined to unconfined settings. In summary, this study provides insights to interpret bedforms in modern and ancient marine volcaniclastic settings elsewhere.