Dome Extrusion Research Articles

Unique seismic and eruption precursors to the 1996 and ongoing magmatic eruptions of Popocatépetl: Coupled and fluidized bed events

We describe three unique types of seismicity at Popocatépetl volcano that accompanied the initial vent-clearing eruptive activity in December 1994 through the eruption of the first two domes in 1996. We identify and describe two types of coupled events, 1) spasmodic burst coupled events, a burst of volcano tectonic (VT) events coupled with a large eruptive explosion (21 December 1994 and 5 March 1996), and 2) explosion-couplet coupled events, a pair of events with a deeper first event and whose second event correlates with a small gas emission or explosion. Explosion-couplets occurred with the onset of magmatic ash dominated eruptions and their properties are very useful for forecasting magmatic eruptions at Popocatépetl volcano. Measurable quantities including the time between the first and second phase, daily numbers of events, and the amplitude ratio between the second and first phase systematically changed as the first two domes approached the surface between March and June 1996. Interevent times decreased from many tens of seconds to a few seconds, while amplitude ratios increased from about 2 to 10 or more. Event numbers increased prior to and during initial dome extrusion. These changes were used to forecast the eruption of the first two domes. We also report on another unusual type of low frequency seismicity that accompanied emissions called fluidized bed events. Fluidized bed events occurred following the initial eruption on 21 December 1994, beginning mid-January 1995, when SO2 emissions were initially elevated, and the conduit was open. Fluidized bed events began to wane in late March through the end of May 1995 as did SO2 emissions. Consistent gas, visual and seismic observations by Centro Nacional de Prevención de Desastres (CENAPRED) enabled the direct correlation of the gas, magma, and seismic phenomena.

СЕМЕЙСТВА ДЛИННОПЕРИОДНЫХ ЗЕМЛЕТРЯСЕНИЙ НА ВУЛКАНЕ МОЛОДОЙ ШИВЕЛУЧ (РОССИЯ) В 2022–2023 ГОДАХ

On April 10, 2023, the strongest eruption of the Young Shiveluch volcano ( Russia, Kamchatka Peninsula) in the last 60 years occurred. The eruption was preceded by a long seismic activity since the end of July 2022. Earthquakes during this period were mainly long-period, occurring in the area of the extruding extrusive dome. The paper describes the grouping of earthquakes into families according to the similarity of waveforms, and their comparison with the activity of the Young Shiveluch volcano. For the period of monotonic, with a constant rate, dome extrusion, when the pressure in the channel was constant, earthquakes were grouped into long-term families. The period before the culmination phase is characterized by a greater number of families, which is interpreted as an indicator of instability of the environment. Such an increase in the number of earthquake families allows us to predict more accurately the beginning of the culmintion phase of eruptions of andesitic Young Shiveluch volcano.

Pre-eruptive magmatic processes at Taranaki volcano from an amphibole perspective

Amphibole phenocrysts in post-1 ka lava domes deposits of Taranaki volcano, an andesite arc volcano in New Zealand, provide an opportunity to explore late-stage changes in melt composition and volatiles in the run up to eruption. Amphibole is a subordinate phase (0–7% of modal phenocrysts) and the phenocrysts display three types of growth history. Type 1 are large compositionally and texturally uniform phenocrysts that have low MgO (<13 wt%) and high K2O (∼1–1.4 wt%) contents. In contrast, Type 2 have similar cores but have been partially resorbed and overgrown by a mafic rim distinguished by high MgO (up to 15 wt%) and low K2O (<1.0 wt%) contents. Type 3 are the least common, and have either normal zoned or concentrically zoned interiors with respect to MgO and FeO. Overall, elemental substitutions and zonation patterns are related to periods of resorption and regrowth that are best explained by changes in melt composition. Based on calculated equilibrium melt compositions, the amphibole crystallisation is consistent with an incrementally grown andesitic to dacitic (SiO2 58–67 wt%) crystal mush that was periodically recharged with more mafic magma (SiO2 ∼ 55 wt%). The melts span a compositional gap (SiO2 ∼ 60–65 wt%) that is not represented in eruption products from the last 8 ka. Such melts were likely brief stages during ongoing fractional crystallisation and magma mixing. Each recharge event disrupted an evolving system and mixed crystals from different parts of it. This concept supports triggering of eruptions by recharge of mafic melts, as also inferred from plagioclase zonation for some eruptions from Taranaki. The outermost rims (0–5 μm) of many amphibole phenocrysts are enriched in fluorine (up to 1.9 wt%) and surrounded by a thick opacitic decomposition growths. We interpret this as the result of slow magmatic ascent and extensive crystallisation that produced a late-stage halogen-rich interstitial melt. This likely extended the conditions for amphibole stability to lower pressure. If F enrichment was accompanied by comparable enrichments in other halogens that preferentially partition into an aqueous phase, then extensive degassing would have occurred during the dome extrusions.

Reconstructing episodic and multi-vent, rhyolitic eruptions: The ∼ 1314 CE Kaharoa eruption of the Tarawera Dome Complex, Okataina Caldera (New Zealand)

Detailed stratigraphic reconstructions and quantitative deposit characterisations of moderate to large-scale rhyolitic eruptions are limited. This hinders our ability to model the multiple eruptive phenomena and hazards associated with rhyolitic volcanism. To gain new perspectives on the patterns and behaviours of rhyolitic eruptions, we present a study on the explosive phases of the 1314 ± 12 CE Kaharoa eruption of Tarawera, New Zealand. The eruption occurred from multiple aligned vents within the Okataina Caldera and is the youngest rhyolitic eruption of the frequently active Taupō Volcanic Zone. We systematically quantify the deposit characteristics of the Kaharoa pyroclastic succession to provide new insights into the type of eruption sequence and eruptive style changes. Based on field evidence, stratigraphic correlations, grain size and componentry analyses, we subdivide the Kaharoa deposit into 24 units and identify 7 main deposit types, which are linked to different eruptive and depositional processes. The explosive activity was discontinuous, characterised by repeated discrete episodes of sustained magma discharge separated by short time breaks. The activity consisted mainly of repeated subplinian-type columns that gave way to fallout deposition and emplacement of numerous lapilli beds. This activity transitioned to a pyroclastic density current (PDC) dominated phase in response to lateral vent migration. Ash emission activity occurred within and towards the end of the explosive sequence, indicating declines in the eruptive intensity. Six main intra-eruption phases (A to F) of dominant eruptive styles are established to describe the temporal evolution of the eruption. Phases A, B and D are associated with the repeated subplinian-type activity. Phase C comprises the major PDC activity, while the final two Phases E and F are associated with ash emission during initiation of lava dome extrusion and to the final dome-building sequence. This study highlights the complex nature of episodic, multi-phase, and multi-vent, explosive to dome-forming rhyolitic eruptions, depicting a scenario of great relevance for future volcanic hazard studies at active rhyolitic volcanoes worldwide.

Excess degassing drives long-term volcanic unrest at Nevado del Ruiz

This study combines volcanic gas compositions, SO2 flux and satellite thermal data collected at Nevado del Ruiz between 2018 and 2021. We find the Nevado del Ruiz plume to have exhibited relatively steady, high CO2 compositions (avg. CO2/ST ratios of 5.4 ± 1.9) throughout. Our degassing models support that the CO2/ST ratio variability derives from volatile exsolution from andesitic magma stored in the 1–4 km depth range. Separate ascent of CO2-rich gas bubbles through shallow (< 1 km depth), viscous, conduit resident magma causes the observed excess degassing. We infer that degassing of ~ 974 mm3 of shallow (1–4 km) stored magma has sourced the elevated SO2 degassing recorded during 2018–2021 (average flux ~ 1548 t/d). Of this, only < 1 mm3 of magma have been erupted through dome extrusion, highlighting a large imbalance between erupted and degassed magma. Escalating deep CO2 gas flushing, combined with the disruption of passive degassing, through sudden accumulation and pressurization of bubbles due to lithostatic pressure, may accelerate volcanic unrest and eventually lead to a major eruption.

Numerical thermomechanical modelling of lava dome growth during the 2007–2009 dome-building eruption at Volcán de Colima

SUMMARY Lava domes form during effusive eruptions due to an extrusion of highly viscous magmas from volcanic vents. In this paper we present a numerical study of the lava dome growth at Volcán de Colima, Mexico during 2007–2009. The mathematical model treats the lava dome extrusion dynamics as a thermomechanical problem. The equations of motion, continuity and heat transfer are solved with the relevant boundary and initial conditions in the assumption that magma viscosity depends on the volume fraction of crystals and temperature. We perform several sets of numerical experiments to analyse the internal structure of the lava dome (i.e. the distributions of the temperature, crystal content, viscosity and velocity) depending on various heat sources and thermal boundary conditions. Although the lava dome growth at Volcán de Colima during short (a few months) dome-building episodes can be explained by an isothermal model of lava extrusion with the viscosity depending on the volume fraction of crystals, we show here that cooling plays a significant role during long (up to several years) episodes of dome building. A carapace develops as a response to a convective cooling at the lava dome–air interface. The carapace becomes thicker if the radiative heat loss at the interface is also considered. The thick carapace influences the lava dome dynamics preventing its lateral advancement. The release of the latent heat of crystallization leads to an increase of the temperatures in the lava dome interior and to a relative flattening of the dome. Meanwhile, the heat source due to viscous dissipation inside the lava dome is negligible, and it does not influence the lava dome growth. The developed thermomechanical model of the lava dome dynamics at Volcán de Colima can be used elsewhere to analyse effusive eruptions, dome morphology and carapace evolution including its failure potentially leading to pyroclastic flow hazards.

New geological and geochronological constraints on the evolution of the Cotacachi - Cuicocha volcanic complex (Ecuador)

Extensive fieldwork at the Cotacachi-Cuicocha Volcanic Complex (CCVC, North of Ecuador) resulted in a new collection of geological data including cartography, chronology, petrography, geochemistry, and morphology. This volcanic complex is formed by a central volcano (Cotacachi: 4939 m asl, current bulk volume of 56 ± 4 km3), several peripheral domes, and a 3 km wide volcanic caldera (Cuicocha: 4.2 ± 0.1 km3). CCVC comprises three stratigraphic members: The first, Cotacachi Basal, represents the initial phase of construction, which started at 173 ± 4 ka with a basal andesitic lava flow succession (∼500 m-thick) including isolated basaltic-andesitic lavas (Verde Tola unit; NE: 113 ± 6 ka, SE: 133 ± 9 ka), the construction of some peripheral amphibole-bearing andesitic domes, such as Muyurcu and Loma Negra (138 ± 4 ka and <108 ka, respectively), and a debris-avalanche deposit to the north-west (0.5–1.8 km3, older than 108 ka). The second member, Upper Cotacachi, consists of an andesitic lava flow succession (∼300 m-thick), younger than 108 ± 6 ka. A gap of activity occurred afterwards from 100 to 70 ka, during which a second debris-avalanche (0.2–1.1 km3, 108 to 65 ka) occurred to the NE, followed by the effusion of the dacitic Piribuela dome (65 ± 2 ka). Afterwards, several superimposed andesitic lava flows were emplaced at the summit, possibly around 15–10 ka since they lack glacial erosion. The third member includes the extrusion of the andesitic Cuicocha pre-caldera domes, which marks the beginning of a new eruptive stage of activity of CCVC during the Holocene, resulting in a violent eruption (3525 ± 35 to 2980 ± 30 a BP; VEI = 5) that partially destroyed the young dome and formed a funnel-shaped caldera (Cuicocha Caldera-Lake), ending with the emplacement of the Wolf and Yerovi post-caldera domes.

Petrology of the explosive deposits from the April 2021 eruption of La Soufrière volcano, St Vincent: a time-series analysis of microlites

Abstract After more than three months of lava dome extrusion, La Soufrière (St Vincent) transitioned to a series of explosive eruptions in April 2021. Here we present a time-series petrologic analysis of the phenocryst and microlite populations during the first c. 48 h of explosivity to constrain ascent conditions and processes that drove changes in behaviour. Primary eruptive products were crystal-rich (45–50 vol%) basaltic andesites with similar phenocryst phase assemblages and compositions. The change in eruptive style is consistent with overpressurization as a consequence of second boiling from anhydrous microlite crystallization. The microlites display variation between the explosive phases, with two populations: (1) ‘inherited’ − normally zoned high-An plagioclase (&gt;An 70 ) + olivine (Fo 62–79 ) + clinopyroxene + titanomagnetite, inferred to have crystallized at depths &gt;15 km and high water pressures; (2) ‘juvenile’ − unzoned plagioclase (An 45–65 ) + clinopyroxene + orthopyroxene + intermediate pyroxene (Wo 12–38 ) + titanomagnetite, inferred to have crystallized upon ascent due to decompression and degassing. Scoria from the first explosions featured extensive groundmass crystallization and a significant ‘inherited’ microlite population. Later explosions had a more abundant ‘juvenile’ microlite population and lower crystallinity, consistent with more rapid ascent from depth, initiated by decompression following initial blasts and destruction of the lava dome.

Petrophysical and Strength Properties of Extrusive Rocks of the Bezymianny Volcano, Kamchatka

For the first time, the results of petrophysical studies of the Bezymianny volcano extrusive rocks from dacites to andesites are presented. A comparative characteristic of the extrusive rocks properties is given according to the selected age groups. The dynamics of changes in the properties of extrusion rocks depending on their age is shown: it is established that the older the rocks, the higher the indicators of their density, strength and elastic properties. The petrophysical features of the rocks of the extrusive domes and lava flows are compared. The applicability of petrophysical properties to clarify the genesis of rocks similar in petrographic characte-ristics, in particular, of extrusive and effusive origin, is substantiated.

The 2013–2020 seismic activity at Sabancaya Volcano (Peru): Long lasting unrest and eruption

Sabancaya volcano is the youngest and second most active volcano in Peru. It is part of the Ampato-Sabancaya volcanic complex which sits to the south of the ancient Hualca Hualca volcano and several frequently active faults, thus resulting in complex volcano-tectonic interactions. After 15 years of repose, in 2013, a series of 4 earthquakes with magnitude >4.5 occurred within 24 h, marking the beginning of a new episode of unrest. Several additional swarms of earthquakes occurred in the following years until magmatic eruptive activity started on 6 November 2016. This activity is ongoing as of this writing, with an average of 50 explosions per day. In this study, we present results of multiparametric monitoring of Sabancaya's activity observed during 2013–2020. Seismic data are used to create a one-dimensional seismic velocity model, to catalog, locate, and characterize earthquakes, to detect repeating earthquake families, and to monitor seismic velocity variations by ambient noise cross-correlation. These analyses are complemented by visual and remote sensing observations and ground deformation measurements. All monitored parameters showed significant changes on 6 November 2016, the day of eruption onset, thus dividing the eruptive activity into pre-eruptive and eruptive stages.The unrest is characterized by high levels of seismic activity with hundreds of events detected per day. Volcano-tectonic (VT) earthquakes were dominant during the pre-eruptive period while long-period (LP) events and explosions have been most numerous since the eruption onset. Earthquake locations highlight long-lasting seismogenic zones along multiple previously active regional faults, as well as along newly identified faults. This VT seismicity is mainly distributed in a sector from the northwest to the east of the volcanic complex at distances of up to 30 km from the crater. We focus our analysis on two eruptive episodes: the eruption onset and subsequent crater migration from south to north, and the increase of lava dome extrusion rate in 2019. Both episodes are accompanied by seismic velocity decreases of up to 0.2% and are preceded by a few weeks by bursts of distal VT activity, including numerous repeating earthquakes. These repeated events were located on several remote tectonic faults (5–25 km from the vent). We suggest that these phenomena could be due to the injection of a batch of magma in the deep reservoir and/or conduit, which would generate 1) a pressure wave propagating in the hydrothermal system, triggering the bursts of seismic activity and 2) slow rising of magma by melting old material filling the conduit that eventually produced the eruptive and dome growth acceleration events.

Rapid pre-explosion increase in dome extrusion rate at La Soufrière, St. Vincent quantified from synthetic aperture radar backscatter

The extrusion rate of a lava dome is a critical parameter for monitoring silicic eruptions and forecasting their development. Satellite radar backscatter can provide unique information about dome growth during a volcanic eruption when other datasets (e.g., optical, thermal, ground-based measurements, etc.) may be limited. Here, we present an approach for estimating volcanic topography from individual backscatter images. Using data from multiple SAR sensors we apply the method to the dome growth during the 2021 eruption at La Soufrière, St. Vincent. We measure an average extrusion rate of 1.8 m3s−1 between December 2020 and March 2021 before an acceleration in extrusion rate to 17.5 m3s−1 in the 2 days prior to the explosive eruption on 9 April 2021. We estimate a final dome volume of 19.4 million m3, extrapolated from the SAR sensors, with approximately 15% of the total extruded volume emplaced in the last 2 days. A possible explanation for the acceleration in extrusion rate could be the combined emptying of a conduit and reservoir of older material before the ascent of gas-rich magma in April 2021.

Crater Lake Kipyashchee of Volcan Golovnin Caldera: Geochemistry of Water and Gases, Output of Magmatic Volitatives (Kunashir Island)

Lake Kipyashchee (Boiling) with an area of ~4.6 ha and a maximum depth of 25 m fills the explosion funnel near one of the extrusive domes of the Golovnin volcano caldera. The water of the lake is ultra-acid (рН = 2.2–2.5) of the chloride-sulfate type with a mineralization of 2.0–2.2 g/l. The water temperature on the surface varies from 30 to 100°C, the average is 37°C. The flow of the lake is carried out through the Protoka in the lake Goryachee (Hot) is 120 l/s (August 2021). The hydrothermal output of magmatic Cl and S (as SO4) from Lake Kipyashchee is 10 t/day and 5.4 t/day, respectively. For the first time, the total diffusive removal of carbon dioxide from the surface of Lake Kipyashchee was estimated as 5.4 tons/day. Obtained from the results of field work in 2020–2021 geochemical data indicate an increase (compared to 2015) in hydrothermal activity in the Golovnin volcano caldera.

Modulation of Popocatépetl’s activity by regional and worldwide earthquakes

Volcanoes switching from quiescence to eruption shortly after catastrophic earthquakes have raised interest for volcanic triggering and the influence of earthquakes on volcanic activity. Its influence on already active systems and especially at open-vent volcanoes is more difficult to apprehend. A number of recent observations suggest an influence of tectonic earthquakes on Popocatépetl’s activity, the importance of which remains unknown. To further investigate this, we introduce an index, based on the near-field concept, identifying the earthquakes with the highest potential to promote volcanic activity (hereafter termed “significant earthquakes”). The time series of significant earthquakes is compared with the intensity of the volcanic activity, as characterized by the number and energy of volcano-tectonic earthquakes, the number of dome extrusions, the intensity of thermal and degassing fluxes, and ash production. Three main periods with contrasting activity stand out showing that Popocatépetl presents intense activity when significant tectonic earthquakes are frequent. Enhanced extrusion apparently follows significant earthquakes quickly with pulses of dome extrusion that peak after 1.3 ± 0.3 years. Conversely, extrusive activity vanishes when significant seismicity disappears, as during the period 2003–2011, which coincides with a 12-year-long significant seismicity gap. Hence, we propose that the 1994–2022 open-vent activity at Popocatépetl is in part modulated by the repetitive occurrence of significant earthquakes that periodically promote volcanic activity.

Monitoring lava dome extrusion of Merapi Volcano during 2018-2019, using low-cost UAV application

Merapi volcano has a well-known eruption type, namely Merapi type, in which an extruded lava dome collapses and is accompanied by pyroclastic density current (PDC). This type of eruption makes morphological monitoring of the lava dome crucial in the hazard mitigation process. After the VEI 4 eruption in 2010, a new lava dome of Merapi appeared on top of the 2010 lava dome in August 2018 and continuously grew. In November 2019, the lava dome started to collapse outward the crater area. We reported the lava dome morphological monitoring using a UAV (Unmanned Aerial Vehicle) photogrammetry conducted from August 2018 to February 2019. This UAV monitoring provides processed aerial photo data in Digital Terrain Model (DTM) and orthophoto with low operating costs and short data acquisition time. The lava domes erupted from the same eruptive canter within this period and grew evenly in all directions. The 2018-2019 Merapi lava dome has basal ratio of 0.183 to 0.290 with height of 11 to 41 m, respectively. Volume changed from 33,623 m3 in August 2018 to 658,075 m3 in February 2019, suggesting growth rate at ~3,500 m3/day. The lava base filled the crater base area (0.21 km2) and started to collapse outward in November 2019.

Numerical Modeling of the Ash Cloud Movement from the Catastrophic Eruption of the Sheveluch Volcano in November 1964

This paper reconstructs, for the first time, the motion dynamics of an eruptive cloud formed during the catastrophic eruption of the Sheveluch volcano in November 1964 (Volcanic Explosivity Index 4+). This became possible due to the public availability of atmospheric reanalysis data from the ERA-40 archive of the European Center for Medium-Range Weather Forecasts (ECMWF) and the development of numerical modeling of volcanic ash cloud propagation. The simulation of the eruptive cloud motion process, which was carried out using the FALL3D and PUFF models, made it possible to clarify the sequence of events of this eruption (destruction of extrusive domes in the crater and the formation of an eruptive column and pyroclastic flows), which lasted only 1 h 12 min. During the eruption, the ash cloud consisted of two parts: the main eruptive cloud that rose up to 15,000 m above sea level (a.s.l.), and the co-ignimbrite cloud that formed above the moving pyroclastic flows. The ashfall in Ust-Kamchatsk (Kamchatka) first occurred out of the eruptive cloud moving at a higher speed, then out of the co-ignimbrite cloud. In Nikolskoye (Bering Island, Commander Islands), ash fell only out of the co-ignimbrite cloud. Under the turbulent diffusion, the forefront of the main eruptive cloud rose slowly in the atmosphere and reached 16,500 m a.s.l. by 04:07 UTC on November 12. Three days after the eruption began, the eruptive cloud stretched for 3000 km over the territories of the countries of Russia, Canada, the USA, Mexico, and over both the Bering Sea and the Pacific Ocean. It is assumed that the well-known long-term decrease in the solar radiation intensity in the northern latitudes from 1963–1966, which was established according to the world remote sensing data, was associated with the spread of aerosol clouds formed not only by the Agung volcano, but those formed during the 1964 Sheveluch volcano catastrophic eruption.

Detecting multiscale periodicity from the secular effusive activity at Santiaguito lava dome complex (Guatemala)

Santiaguito, Guatemala, represents one of the best cases of active lava dome complex in the world, producing lava flow effusion, weak explosive activity, and cycles of lava dome extrusion over varying timescales. Since the inception in 1922, it has shown a remarkable constant eruptive activity, characterized by effusion of blocky domes and lava flows punctuated by moderate explosions of gas-and-ash and pyroclastic flows. In this study, we reconstruct the time evolution of discharge rates of Santiaguito across one entire century, from 1922 to 2021, combining, for the more recent activity, new satellite thermal data. By using discrete Fourier transform (DFT) and Morlet wavelet analyses, we identify three fundamental periodicities in subsets of the 1922–2021 time-series: (i) long term (ca. 10 years), (ii) intermediate term (ca. 3.5 years), and (iii) short term (from ca. 1 year to ca. 3 months), which are comparable with those observed at other lava dome eruptions at calc-alkaline volcanoes. Such inferred periodicities provide a powerful tool for the interpretation of the non-linear eruptive behaviour and represent a pivotal benchmark for numerical modelling aimed to reconstruct the dynamics of the magma feeding system based on a time-averaged discharge rate dataset.Graphical

Magma buoyancy drives rhyolitic eruptions: A tale from the VEI 5 2008-2009 Chaitén eruption (Chile) from seismological and geodetic data

Magma buoyancy is a mechanism usually neglected with respect to magma overpressure in eruption models constrained with geophysical data. In this study we provide evidence for a buoyancy-driven mechanism of magma ascent during the effusive phase of the 2008-2009 Chaitén rhyolitic eruption. We also constrain the volcano plumbing system with source models from InSAR and teleseismic data. InSAR data did not detect unambiguous evidence of pre-eruptive ground deformation up to 1 year before the eruption. Teleseismic data indicate that a dike opened twice during the first two days of the eruption, while InSAR data show that three sources deflated during the eruption. These include one dike and a sill during the onset of the eruption, and a spherical source halfway through it, all located at depths between 3 and 12 km. 75% of the total ground deformation of ∼0.5 m occurred during the first three weeks of the eruption. A Pléiades DEM show that the dome has a bulk volume of 1 km3, and was extruded with an exponential trend, but the lack of deformation during most of the effusive phase of the eruption implies that the dome extrusion did not result in depressurization of a magma reservoir. Instead, we show that the time series of extruded volume can be explained by magma ascending due its buoyancy instead of its overpressure. Further, the end of the first pulse of dome effusion in September 2008 can be explained by an increase in the dome surface load that equals the effect of the magma buoyancy. These results imply that in some cases ground deformation data alone cannot be used to forecast the temporal evolution of an eruption. They also call for the acquisition of denser time series of extruded volume, as a way to better constrain their evolution through time.

Geochronological evolution of the potentially active Iliniza Volcano (Ecuador) based on new K-Ar ages

The youngest volcanism of the Ecuadorian Volcanic Front (Western Cordillera) is mainly dominated by highly explosive events, including the growth and violent destruction of lava domes, and the formation of thick pyroclastic sequences. Deposits associated with such eruptive dynamics have been identified at Iliniza, a compound volcano located in the Western Cordillera with a poorly defined evolutionary history. We present the first K-Ar ages of Iliniza volcano combined with stratigraphic data, numerical reconstructions, and geochemical analyses, providing a new perspective on its evolution. Our results show that Iliniza volcano is much younger than previously proposed. The Iliniza twin-peaked shape is the result of the superposition of two andesitic to dacitic stratovolcanoes. (1) The North Iliniza (NI) edifice was constructed by two lava successions and an intermediate satellite vent, showing a short range of mainly effusive activity between 123 ± 6 and 116 ± 2 ka. (2) The South Iliniza (SI) edifice began its construction through the Lower SI stage when massive lavas dated at ~45 ka formed a basal cone. During the Upper SI stage, the uppermost part of this edifice was destroyed by the highly explosive Jatuncama phase (VEI 5) leaving a 30–40 m-thick ignimbrite sequence. The subsequent extrusion of several dacitic lava domes reconstructed the South Iliniza summit at around 35 ka. The Terminal SI stage corresponds to the emission of several andesitic lavas between 31 ± 4 and 25 ± 3 ka. The Iliniza eruptive activity extended into the Late Pleistocene and Holocene with the extrusion of the Tishigcuchi lava dome, and the emission of the Pongo lava flow dated at 6 ± 4 ka. Based on the proposed eruptive history, we suggest that a revised volcanic hazard assessment of the potentially active Iliniza volcano is required.

Present sedimentation in the volcanic lakes of the Kurile-Kamchatka region (Russia) as a basis for paleoreconstructions

Abstract. The results of modern processes observations of the sedimentation in the volcanic lakes of the region are summarized with the use of material from other regions of the world. The available data on the drained volcanic lakes deposits, Uzon-Geysernaya caldera as example, was analysed. The main sources of material (volcanic and post-volcanic activity, gravitational displacements on slopes, and erosion-denudation processes) and the mechanisms of its entry into volcanic lakes, as well as the features of the subsequent deposits transformation as a result of hydrothermal, seismic, and volcano-tectonic activity, are identified. The results of the studies carried out allow us to conclude that the volcanic lakes deposits are complexly constructed polyfacial complexes with alternating fine-grained lacustrine and lacustrine-swamp deposits with pyroclastic horizons and interlayers of untreated or poorly processed coarse clastic material coming as a result of volcano-tectonic activity, gravitational and erosion processes. The irregularity of horizons along strike is typical; and is characterized by the large-scale sediments deformation under the influence of seismic activity, growth of effusive and extrusive domes, phreatic explosions, etc. Hydrothermal activity contributes to the weathering and cementation of the lake sediments. Lava outpourings and the high-temperature pyroclastic flows provokes sintering of contacting horizons sediments.

Volcanic activity accompanying the emplacement of dacitic lava domes and effusion of lava flows at Nevados de Chillán Volcanic Complex – Chilean Andes (2012 to 2020)

Nevados de Chillán volcanic complex (NChVC) is one of the most active volcanoes in Chile having 4 eruptive episodes within the previous century. All of this activity has been concentrated within Las Termas sub-complex, the last eruption before the current reactivation occurred in 2008 characterized by a lava flow toward the east side of the edifice. The first surficial manifestation was an explosive event occurred on January 8, 2016, NChVC has been in eruption since then and continuing today. Seismicity has shown a variety of waveforms and types: Long Period (LP), Tornillo (TO), Very Long Period (VLP), spasmodic tremor, harmonic tremor and Volcano Tectonic (VT) earthquakes. Reactivation was marked by an increase in LP seismicity accompanied by a more regular VT activity. Based on seismicity, morphological changes and some petrological features it has determined five phases of activity, from hydrothermal dominance up to different magmatic episodes. It includes a lava dome extrusion, alternate growing and destruction of it, effusion of four lava flows. It is remarkable the low flow rates observed on extrusion and effusion of lava bodies (0.008 m3/s-0.04 m3/s), the constant vulcanian type eruptions of low and middle intensity, the occurrence of piroclastic flows mainly toward north and northeast to the crater and deformation process absent in the lava dome extrusion and very clear during lava flows effusion. This work makes a broad description of multiparametric data acquired by the monitoring network from 2012 to 2020, in order to illuminate the internal and external processes acting during the NChVC crisis and a hypothetical model of the magmatic plumbing system is proposed. This model states the presence of a magma plug in the shallow (0.5–1.1 km) conduit reactivated by at least two intrusive processes from 4 to 6 km depth magma chamber following the trend of a major fault structure, Cortaderas fault, which controls the distribution of eruptive centers of the complex. Our results could contribute also, to understand the behavior of the magmatic systems that produce dacitic lava domes with low volume and low growing rates.