Sector Collapse Research Articles

Volcanic Lateral Collapse Processes in Mafic Arc Edifices: A Review of Their Driving Processes, Types and Consequences

Volcanic cones are frequently near their gravitational stability limit, which can lead to lateral collapse of the edifice, causing extensive environmental impact, property damage, and loss of life. Here, we examine lateral collapses in mafic arc volcanoes, which are relatively structurally simple edifices dominated by a narrow compositional range from basalts to basaltic andesites. This still encompasses a broad range of volcano dimensions, but the magma types erupted in these systems represent the most abundant type of volcanism on Earth and rocky planets. Their often high magma output rates can result in rapid construction of gravitationally unstable edifices susceptible both to small landslides but also to much larger-scale catastrophic lateral collapses. Although recent studies of basaltic shield volcanoes provide insights on the largest subaerial lateral collapses on Earth, the occurrence of lateral collapses in mafic arc volcanoes lacks a systematic description, and the features that make such structures susceptible to failure has not been treated in depth. In this review, we address whether distinct characteristics lead to the failure of mafic arc volcanoes, or whether their propensity to collapse is no different to failures in volcanoes dominated by intermediate (i.e., andesitic-dacitic) or silicic (i.e., rhyolitic) compositions? We provide a general overview on the stability of mafic arc edifices, their potential for lateral collapse, and the overall impact of large-scale sector collapse processes on the development of mafic magmatic systems, eruptive style and the surrounding landscape. Both historical accounts and geological evidence provide convincing proofs of recurrent (and even repetitive) large-scale (>0.5 km3) lateral failure of mafic arc volcanoes. The main factors contributing to edifice instability in these volcanoes are: (1) frequent sheet-like intrusions accompanied by intense deformation and seismicity; (2) shallow hydrothermal systems weakening basaltic rocks and reducing their overall strength; (3) large edifices with slopes near the critical angle; (4) distribution along fault systems, especially in transtensional settings, and; (5) susceptibility to other external forces such as climate change. These factors are not exclusive of mafic volcanoes, but probably enhanced by the rapid building of such edifices.

Construction of an intraplate island volcano: The volcanic history of Heard Island

Heard Island is a subantarctic volcanic island in the southern Indian Ocean and includes Australia’s only active volcano, Big Ben (2813 m high, 18 km diameter). The most recent eruption of lava at Big Ben occurred in November 2020. Heard Island is the southernmost subaerial exposure of the Kerguelen Plateau, a mainly submerged large igneous province formed as a result of the activity of the Kerguelen plume over the last 130 Myrs. Using published and unpublished data and reports, modern satellite images, and private and public rock collections, we produced a new geological map of Heard Island supplemented by new 40Ar/39Ar isotopic ages. The volcanoes on Heard Island have been constructed on a ~ 300-m-thick platform of 10–5-Myr-old submarine volcaniclastic rocks known as the Drygalski Formation, now exposed above sea level. The Drygalski Formation is underlain by the Oligocene Laurens Peninsula Limestones. Exposed Big Ben lavas are dominated by basanite, basalt, and trachybasalt compositions. Two Big Ben lavas were dated at 11.1 ± 1.1 ka and 23.9 ± 2.1 ka, expanding the range of ages previously reported for nonhistorical lavas from Big Ben (356 ± 51–33 ± 52 ka). Sector collapse occurred on Big Ben prior to the formation of the current eruptive centre, Mawson Peak (likely after 23 ± 16 ka). Laurens Peninsula lies to the west of Big Ben and consists of trachyte and basanite lavas and domes. Laurens Peninsula lavas have ages in the range 5.1 ± 3.5 to 76.6 ± 5.5 ka. Young basaltic cones are located around the coast of Heard Island and range in age from 1.9 ± 3.8 to 13.3 ± 4.1 ka. Heard Island is a relatively small volcanic edifice with a low average magma discharge rate (~0.0002 km3/yr) when compared with other intraplate basaltic volcanic islands.

The Tutupaca volcanic complex (Southern Peru): Eruptive chronology and successive destabilization of a dacitic dome complex

Several processes have been proposed as triggering mechanisms for the large sector collapses that affect most volcanoes, and which may occur several times in the volcano's lifetime. Here we present and discuss the case of Tutupaca volcano, located in southern Peru and part of the Central Volcanic Zone of the Andes. Tutupaca is composed of an old, hydrothermally altered and highly eroded Basal edifice, as well as younger twin peaks located in the northern part of the complex (the Western and Eastern Tutupaca). The youngest Eastern edifice of Tutupaca is composed of at least seven coalescing lava domes and associated deposits, including block-and-ash flow and debris avalanche deposits. We identified two debris avalanche deposits. An older unit (Azufre debris avalanche deposit) was channeled in the valleys located to the E and SE of the basal volcano, reaching up to 3.5 km from its source region. Four cosmogenic nuclide exposure dates (10Be/feldspar) were obtained from boulders of this debris avalanche deposit and ranged between 6.0 ± 0.7 and 7.8 ± 1.5 ka. The younger unit (Paipatja deposit) was associated with the sector collapse of the edifice reconstructed just after the first debris avalanche (domes IV to VIII). The sector collapse produced a debris avalanche deposit that outcrops immediately to the NE of the amphitheater and was associated with a large pyroclastic density current deposit that was previously dated by radiocarbon at 218 ± 14 a BP (Samaniego et al., 2015). Both debris avalanche deposits have two contrasting sub-units: (1) the main subunit, hereafter called hydrothermal-altered debris avalanche deposit, is a whitish-yellow volcanic breccia with heterolithic and heterometric blocks, which originated from the Basal edifice, and (2) a dome-rich debris avalanche deposit, composed by non-altered dome blocks from Eastern Tutupaca. In proximal areas, the dome-rich unit overlaps the hydrothermally-altered unit while in distal areas, these two units are mixed forming a hummocky and/or ridged topography. In addition to the similarity of both debris avalanches, we propose that the triggering mechanism for these debris avalanches was similar. The dacitic dome growth, coupled with a substrate of older, hydrothermally-altered rock, induced the destabilization of the edifice, producing the debris avalanches and the related pyroclastic density currents.

「液状化」ですべる話2題：1792年雲仙眉山崩壊と1783年浅間山鎌原土石なだれ

「液状化」ですべる話2題：1792年雲仙眉山崩壊と1783年浅間山鎌原土石なだれ

Impact of Covid-19 in India: Issues , Challenges and Opportunities

The first case of COVID-19 was detected in Wuhan city of China. The mysterious virus believed to have been spread by the sea food or bat. In a few days ,it gripped the entire world. Consequently, WHO(World Health Organisation) had to declare it a pandemic. There was no option before the world except social distancing and lockdown to keep safe from it. There are a number of issues such as disruption of supply chain, shutdown of core manufacturing sectors , loss of revenues from railways, aviation, tourism, unemployment, problems of the migrant workers, poverty , collapse of informal sectors, Micro Small and Medium enterprises and e-commerce. There are challenges before the country to deal with these issues as how to manage the survival , provide employment, eradicate poverty and improve the health sector. The country can seek various opportunities from lockdown such as utilisation of manpower , information and machine technology. The positive impact of lockdown has fallen on environment. Pollution levels have come down. Air has cleaned and Air Quality Index has improved. The paper examines the impact of lockdown, issues of economic growth as well as the opportunities wrought from the crisis.

Volcanic Hazard Assessment for an Eruption Hiatus, or Post-eruption Unrest Context: Modeling Continued Dome Collapse Hazards for Soufrière Hills Volcano

Effective volcanic hazard management in regions where populations live in close proximity to persistent volcanic activity involves understanding the dynamic nature of hazards, and associated risk. Emphasis until now has been placed on identification and forecasting of the escalation phase of activity, in order to provide adequate warning of what might be to come. However, understanding eruption hiatus and post-eruption unrest hazards, or how to quantify residual hazard after the end of an eruption, is also important and often key to timely post-eruption recovery. Unfortunately, in many cases when the level of activity lessens, the hazards, although reduced, do not necessarily cease altogether. This is due to both the imprecise nature of determination of the “end” of an eruptive phase as well as to the possibility that post-eruption hazardous processes may continue to occur. An example of the latter is continued dome collapse hazard from lava domes which have ceased to grow, or sector collapse of parts of volcanic edifices, including lava dome complexes. We present a new probabilistic model for forecasting pyroclastic density currents (PDCs) from lava dome collapse that takes into account the heavy-tailed distribution of the lengths of eruptive phases, the periods of quiescence, and the forecast window of interest. In the hazard analysis, we also consider probabilistic scenario models describing the flow’s volume and initial direction. Further, with the use of statistical emulators, we combine these models with physics-based simulations of PDCs at Soufrière Hills Volcano to produce a series of probabilistic hazard maps for flow inundation over 5, 10, and 20 year periods. The development and application of this assessment approach is the first of its kind for the quantification of periods of diminished volcanic activity. As such, it offers evidence-based guidance for dome collapse hazards that can be used to inform decision-making around provisions of access and reoccupation in areas around volcanoes that are becoming less active over time.

The hydrothermal system associated with Miocene Chimpa volcano, Central Andes. Implications on potential mineralization

Miocene volcanism in the central sector of the Puna plateau, in the back–arc region of the Central Andes, has important economic potential, because it is associated with many epithermal ore deposits. Chimpa volcano is one of the largest stratovolcanoes of this region, hosting hydrothermal alteration. In order to map and characterize the hydrothermal alteration, multispectral ASTER satellite imagery, fieldwork, petrography, XRD and Raman spectroscopy have been used. Our study allowed identifying two alteration zones: alunite + illite + jarosite, and alunite + illite. The alunite + illite + jarosite zone occurs mainly in the center of Chimpa volcano, corresponding to the vent area and covering an area of ~0.02 km2. The alunite + illite zone covers a wider area mainly surrounding the alunite + illite + jarosite region, extending to the east and west and covering an area of ~2.5 km2. Small altered zones observed away from the vent area have been incorporated in mass-wasting and sector collapse deposits. Therefore, the hydrothermal alteration zone may be actually narrower than the area occupied by altered rocks. The absence of ore minerals indicates a potential barren hydrothermal system. However, the recognized alteration zones, together with the presence of vuggy silica and hypogene alunite, suggest that Chimpa volcano could host a volcanic-hydrothermal leached system related to the emplacement of a volcanic dome complex in the summit area. The hydrothermal system was set up in the final stage or immediately after the dome emplacement phase. Further prospection studies, such as geophysical techniques and drilling, should be focused on finding out if the Chimpa volcano hosts a mineralized system or is a non-economic acidic alteration.

The rebirth and evolution of Bezymianny volcano, Kamchatka after the 1956 sector collapse

Continued post-collapse volcanic activity can cause the rise of a new edifice. However, details of such edifice rebirth have not been documented yet. Here, we present 7-decade-long photogrammetric data for Bezymianny volcano, Kamchatka, showing its evolution after the 1956 sector collapse. Edifice rebirth started with two lava domes originating at distinct vents ~400 m apart. After 2 decades, activity became more effusive with vents migrating within ~200 m distance. After 5 decades, the activity focused on a single vent to develop a stratocone with a summit crater. We determine a long-term average growth rate of 26,400 m3/day, allowing us to estimate the regain of the pre-collapse size within the next 15 years. Numerical modeling explains the gradual vents focusing to be associated with loading changes, affecting magma pathways at depth. This work thus sheds light on the complex regrowth process following a sector collapse, with implications for regrowing volcanoes elsewhere.

Evolution of the Quaternary silicic volcanic complex of Shiribetsu, Hokkaido, Japan: an example of ignimbrite shield volcanoes in an island arc setting

This paper describes the geology and eruptive history of a Quaternary silicic volcanic complex at Shiribetsu, Hokkaido, Japan, with a focus on volcanic landforms produced by silicic explosive eruptions that were not associated with caldera collapse. The Shiribetsu volcanic complex comprises a dacitic pyroclastic plateau and an overlying dacitic central dome complex. The pyroclastic plateau is 22 × 25 km in size, < 200 m high, and consists of two ignimbrite units (the Km-1 and Km-2 deposits; SiO2 = 67–68 wt%; total volume ~ 10 km3). The central dome complex is 4–5 km wide, rises to 650 m above the pyroclastic plateau, and comprises two adjoining edifices, which are East and West Shiribetsu (SiO2 = 62–64 wt%; total volume = 1.6 km3). East Shiribetsu has a conical morphology, whereas West Shiribetsu comprises lava flows and a dome, and has a large amphitheater. A debris avalanche deposit (volume = 1 km3) extends from the amphitheater to the western foot of West Shiribetsu. A dacitic lava dome (volume = 0.2 km3) occurs within the amphitheater. According to the stratigraphic relationships and new fission-track dating, the Shiribetsu volcanic complex evolved as follows: (1) dacitic explosive eruptions at ca. 130 ka (Km-2) and 70 ka (Km-1) produced the pyroclastic plateau; (2) effusive dacitic eruptions at 70 ka (East Shiribetsu) and 60 ka (West Shiribetsu) produced the central dome complex; (3) sector collapse occurred at West Shiribetsu at 50–60 ka; and (4) lava dome formation within the amphitheater at 50 ka. The evolution of the Shiribetsu volcanic complex resembles that of ignimbrite shield volcanoes in the central Andes. Shiribetsu may be the first identified example of ignimbrite shield volcanoes in an island arc setting. We suggest that these are an independent class of explosive silicic volcanoes, distinct from calderas, and form above small magma chambers.

The 1951 eruption of Mount Lamington, Papua New Guinea: Devastating directed blast triggered by small-scale edifice failure

The catastrophic explosion of Mount Lamington volcano, Papua New Guinea on January 21, 1951 produced a devastating pyroclastic density current (PDC) that knocked down dense tropical rainforest over an area of 230 km2 and killed approximately 3000 people. We present results of a field reinvestigation of the 1951 PDC deposit combined with an analysis of the available photographs and eyewitness accounts of the eruption first published in the fundamental work of G. A. M. Taylor (1958).We have concluded that the six-days-long pre-climactic activity before the 1951 eruption (which included felt local seismicity, frequent ash-laden explosions of vulcanian type, bulging of the volcano slope accompanied with landslides) was associated with shallow-level intrusion of a highly viscous magma body (cryptodome/dome) of andesitic composition with a volume of approximately 0.01 km3. This intrusion destabilized Mount Lamington's prehistoric intra-crater lava dome.On January 21 the destabilized dome gravitationally collapsed and produced a relatively small-volume debris avalanche, the deposit of which was not recognized during Taylor's original investigation. The debris avalanche had a volume of approximately 0.02–0.04 km3, travelled a distance (L) of 8.5 km and had the ratio of vertical drop (H) to runout (L) of 0.14. The edifice collapse decompressed the intruding cryptodome and triggered its explosive fragmentation.Photographs of the climactic explosion show that the eruptive cloud initially rose vertically but subsequently collapsed upon the terrain around the vent, and formed a PDC which flowed radially outward. The enhanced northward propagation of the PDC to a maximum distance of 13 km reveals that the northern breach in the ancient crater's high walls influenced the distribution of the deposit. In the studied NE-N-NW sector of the devastated area, in the zone proximal to the volcano, the PDC emplaced a normally graded layer of coarse ash and lapilli mixed in the base with picked-up soil and plant fragments. The layer gradually becomes thinner and finer-grained with distance from the volcano. The PDC deposit has a volume of approximately 0.025 km3 and consists of approximately 80% juvenile rock fragments derived from the explosively fragmented cryptodome. The remaining 20% consists of accidental clasts derived from the old volcanic edifice. The juvenile material is crystal-rich andesite with a unimodal vesicularity distribution (4 to 36%). The reconstructed eruption sequence, the PDC tree blowdown pattern and characteristics of the PDC deposit are similar to those of catastrophic laterally-directed blasts of volcanoes Bezymianny in 1956, Mount St.Helens in 1980, and Soufriere Hills, Montserrat in 1997. In contrast to the cases of these “classic” lateral blasts, the blast cloud of Lamington was initially vertically-directed before collapsing to produce a PDC. We speculate that the climactic explosion of Mount Lamington was initially vertical because the rupture surface of the triggering sector collapse intersected the apex of the intruding cryptodome (it exposed a subhorizontal surface of the cryptodome apex), while at Bezymianny, Mount St.Helens, and Soufriere Hills the rupture intersected the main body of the cryptodome/dome, and exposed their steeply inclined surfaces.

Transport and Evolution of Supercritical Fluids During the Formation of the Erdenet Cu–Mo Deposit, Mongolia

Petrological and fluid inclusion data were used to characterize multiple generations of veins within the Erdenet Cu–Mo deposit, Mongolia, and constrain the evolution of fluids within the magmatic–hydrothermal system. Three types of veins are present (from early to late): quartz–molybdenite, quartz–pyrite, and quartz. The host rock was emplaced at temperatures of 700–750 °C, the first quartz was precipitated from magma-derived supercritical fluids at 650–700 °C, quartz–molybdenite and quartz–pyrite veins were formed at ~600 °C, and the quartz veins were precipitated in response to retrograde silica solubility caused by decreasing temperatures at &lt;500 °C. We infer that over-pressured fluid beneath the cupola caused localized fluid injection, or that accumulated stress caused ruptures and earthquakes related to sector collapse; these events disrupted impermeable layers and allowed fluids to percolate through weakened zones.

Combining 3D seismics, eyewitness accounts and numerical simulations to reconstruct the 1888 Ritter Island sector collapse and tsunami

The 1888 Ritter Island volcanic sector collapse triggered a regionally damaging tsunami. Historic eyewitness accounts allow the reconstruction of the arrival time, phase and height of the tsunami wave at multiple locations around the coast of New Guinea and New Britain. 3D seismic interpretations and sedimentological analyses indicate that the catastrophic collapse of Ritter Island was preceded by a phase of deep-seated gradual spreading within the volcanic edifice and accompanied by a submarine explosive eruption, as the volcanic conduit was cut beneath sea level. However, the potential impact of the deep-seated deformation and the explosive eruption on tsunami genesis is unclear. For the first time, it is possible to parameterise the different components of the Ritter Island collapse with 3D seismic data, and thereby test their relative contributions to the tsunami. The modelled tsunami arrival times and heights are in good agreement with the historic eyewitness accounts. Our simulations reveal that the tsunami was primarily controlled by the displacement of the water column by the collapsing cone at the subaerial-submarine boundary and that the submerged fraction of the slide mass and its mobility had only a minor effect on tsunami genesis. This indicates that the total slide volume, when incorporating the deep-seated deforming mass, is not directly scalable for the resulting tsunami height. Furthermore, the simulations show that the tsunamigenic impact of the explosive eruption energy during the Ritter Island collapse was only minor. However, this relationship may be different for other volcanogenic tsunami events with smaller slide volumes or larger magnitude eruptions, and should not be neglected in tsunami simulations and hazard assessment.

Frontal Aureole Deposit on Acheron Fossae ridge as evidence for landslide-generated tsunami on Mars

The recurrent failures of the 8 to 10-km high basal scarp of the Olympus Mons volcano on Mars has resulted in enormous landslides merging into a composite deposit known as the aureole. The largest of these landslides, the western (W) aureole, appears as a hummocky and extensive tongue reaching the distance of 700 ​km from the present Olympus Mons edge. Totalizing a volume of 106 Km3, the W aureole was created by a single, 100°-wide sector collapse of the Olympus Mons flank between north and west directions. Whereas the western segment of the landslide fell onto the flat area of Amazonis Planitia, the northern section came across the gently sloping ridge of Acheron Fossae after 550 ​km of travel, and subsequently rose against slope for some additional 50–80 ​km.Analysis of imagery on Acheron Fossae ridge beyond the front of the landslide shows a peculiar deposit and associated morphologies. Termed here Frontal Aureole Deposits (FAD), it occurs in two units: a smooth, uniform deposit immediately beyond the aureole terminus, followed in the distal part by distinct lobes directed against slope. These deposits are interpreted as the remnants of debris-rich sandy and muddy waves thrust by the W aureole landslide that inundated the Acheron Fossae ridge. Numerical and analytical calculations set up to study the dynamics of inundation show that the length of the deposits was in the reach of water thrust by a fast-travelling landslide. A possible explanation for the presence of water is that the front was travelling across an outlet of the ancient Martian ocean which, consequently, must have persisted when the landslide event took place. According to this hypothesis, FAD represents the remnant of a giant tsunami deposit similar, albeit at a much larger scale, to those that occur on Earth.

The evolution of bank bailout policy: two centuries of variation, selection and retention

Why has the policy of state-backed bank bailouts emerged as the de facto global response by governments to crises involving systemic bank risk? This question has salience in the context that while bank bailouts solve an immediate problem of systemic risk, they create another set of problems almost as significant. Bailouts involve largescale socialization of private losses, are politically toxic, ideologically contrary to market norms, and economically costly to the state. For these reasons many commentators view the policy to be neither optimal nor desirable, yet it has nonetheless been institutionalized in all modern financial systems. In this paper I argue that the global diffusion of bank bailout policy over the past two centuries is an example of institutional evolution. A process of variation, selection and retention has winnowed down initial variation in responses to possible financial sector collapse to one policy, a state-backed guarantee to bail out the financial system. Understanding the past is a prerequisite for gaining insight into possible futures. Consequently, historical study of bank bailouts will contribute to understanding the future evolution of systemic banking crises by providing insight into the evolution of institutional resilience.

Unusual volcanic instability and sector collapse configuration at Chimpa volcano, central Andes

Upper Miocene Chimpa volcano is one of the largest stratovolcanoes of the back–arc region of the central Andes. The gentle–sloped volcano underwent previously unrecognized volcanic instability, consisting of ≈ 2 km3 mass–wasting processes and catastrophic sector collapse, whose characteristics have been identified by means of stratigraphy, geological mapping and structural analysis. The origin of instability at Chimpa can be attributed to tectonic faulting, hydrothermal alteration and overloading. These common promoting and triggering factors have produced an unusual configuration of the volcano gravitational instability, characterized by parallel landslide scars delimiting unstable sectors on eastern and western volcano flanks, with large toreva blocks sliding in opposite directions, perpendicular to the flow direction of a subsequent long–run out debris avalanche. Even if the style of such a complex volcanic instability has never been described before, its identification may be also useful to study volcano sector failures and mass–wasting deposits in other volcanoes worldwide.

Infrastructure of Sustainable Energy Development in Pakistan: A Review

Pakistan is an energy-resourceful country with vast and untapped renewable energy sources (RESs). The wind, solar, and biomass of the country are practically capable of ending a power sector collapse caused by demand-supply variances. A significant percentage of Pakistan's population resides in rural areas. For rural population, the lack of connection to the mainstream of national development is a direct consequence of frequent power blackouts and, in certain cases, a lack of grid connection altogether. Lucrative features of smart grid are not fully incorporated into the power network yet, but policy-makers are paying attention to increase RES reliance. A comprehensive study describing the renewable energy potential of Pakistan is of importance. This research work attempts to present a collective summary of Pakistan's renewable energy potential. A statistical analysis of the proposed and installed projects in various districts are presented. This paper elaborates the pressing needs of renewable energy integration for resolving Pakistan's energy crisis. Renewable energy projects are acclaimed in this paper for affording higher living standards and better job opportunities than the fossil fuel based industry in Pakistan. Integrating RESs into the national portfolio is guaranteed to offer profound socio-economic benefits to Pakistan's rural population.

Pyroclastic deposits and eruptive heterogeneity of Volcán Antuco (37°S; Southern Andes) during the Mid to Late Holocene (

Volcán Antuco (37°24′ S, 71°22′W; 2979 m asl) is the 13th ranked high threat volcano in Chile with 27 recorded historical eruptions, mostly (~96%) with volcanic explosivity indices (VEI) of ~1–2. An older eruptive record has been reconstructed from sections exposed on the western flank and is intimately related to a well-documented catastrophic sector collapse at ~7.2 cal ka BP. However, very little is known about Antuco's post-collapse eruptive history in other sectors, especially on the eastern flanks where prevalent westerly winds favor optimal eastward tephra transport and deposition. Our study reveals a more complete record of activity that has already been indicated from previous work with at least 23 tephra-forming explosive eruptions, most of them within the last c. 7.2 ka, including 4 events that have generated pyroclastic density currents that have widely inundated the lower eastern flanks. Tephra from these eruptive events are typically composed of scoria, free crystals and lithics, with occasional pumice. The composition of juvenile fragments varies between basalt and trachyandesite (50.2–62.2 wt% SiO2) and show phenocrysts of plagioclase, olivine and pyroxene. Our results show that most of the eruptions of Antuco (c. 79%) are Strombolian to violent Strombolian. These eruptions have an estimated longer repose times (c. 200 year) and are likely higher in magnitude than those registered during historical times. This study also shows that the composition, style and magnitude may change from one eruptive episode to the next. This eruptive variability seems in complete accord with recent findings from other centers in the Southern Volcanic Zone exhibiting similar temporal eruptive diversity and ultimately, has significant implications with respect to hazard assessment.

Growth and collapse of a littoral lava dome during the 2018/19 eruption of Kadovar Volcano, Papua New Guinea, analyzed by multi-sensor satellite imagery

Growing volcanic islands and lava domes become structurally unstable, associated with sectoral collapses, explosive volcanism and related hazards. This article describes the rare case of a growing and collapsing lava dome at Kadovar Volcano, a small inhabited volcanic island located north of Papua New Guinea. The eruption began on January 5, 2018 and was monitored by multi-sensor satellite imagery, including optical, thermal and synthetic aperture radar (SAR) sensors. Results show that Kadovar began a new episode of volcanic activity at the central crater and then also at the eastern coast of the island. SAR amplitude imagery has made it possible to monitor the birth of a new peninsula on the eastern coast. This new peninsula has a blocky appearance and is associated with a localized thermal anomaly, which is indicative of an emerging lava dome. We analyzed the changes on the island and the peripheral lava dome and found that after a great increase in the size of the area, parts of the island and the lava dome then collapsed eastwardly into the ocean on February 9, 2018. The sector collapse caused small tsunami waves that hit the neighboring islands. A subsequent slower re-growth of the lava dome is evident from the satellite data, which has reached a final area of ˜40,000 m². This study provides details on the rapid growth and collapse of a peripheral lava dome and a destabilization episode in an island and dome sector, and underlines the great value of remote sensing data on remote volcanic islands.

Complex hazard cascade culminating in the Anak Krakatau sector collapse

Flank instability and sector collapses, which pose major threats, are common on volcanic islands. On 22 Dec 2018, a sector collapse event occurred at Anak Krakatau volcano in the Sunda Strait, triggering a deadly tsunami. Here we use multiparametric ground-based and space-borne data to show that prior to its collapse, the volcano exhibited an elevated state of activity, including precursory thermal anomalies, an increase in the island’s surface area, and a gradual seaward motion of its southwestern flank on a dipping décollement. Two minutes after a small earthquake, seismic signals characterize the collapse of the volcano’s flank at 13:55 UTC. This sector collapse decapitated the cone-shaped edifice and triggered a tsunami that caused 430 fatalities. We discuss the nature of the precursor processes underpinning the collapse that culminated in a complex hazard cascade with important implications for the early detection of potential flank instability at other volcanoes.

Modelling of the tsunami from the December 22, 2018 lateral collapse of Anak Krakatau volcano in the Sunda Straits, Indonesia

On Dec. 22, 2018, at approximately 20:55–57 local time, Anak Krakatau volcano, located in the Sunda Straits of Indonesia, experienced a major lateral collapse during a period of eruptive activity that began in June. The collapse discharged volcaniclastic material into the 250 m deep caldera southwest of the volcano, which generated a tsunami with runups of up to 13 m on the adjacent coasts of Sumatra and Java. The tsunami caused at least 437 fatalities, the greatest number from a volcanically-induced tsunami since the catastrophic explosive eruption of Krakatau in 1883 and the sector collapse of Ritter Island in 1888. For the first time in over 100 years, the 2018 Anak Krakatau event provides an opportunity to study a major volcanically-generated tsunami that caused widespread loss of life and significant damage. Here, we present numerical simulations of the tsunami, with state-of the-art numerical models, based on a combined landslide-source and bathymetric dataset. We constrain the geometry and magnitude of the landslide source through analyses of pre- and post-event satellite images and aerial photography, which demonstrate that the primary landslide scar bisected the Anak Krakatau volcano, cutting behind the central vent and removing 50% of its subaerial extent. Estimated submarine collapse geometries result in a primary landslide volume range of 0.22–0.30 km3, which is used to initialize a tsunami generation and propagation model with two different landslide rheologies (granular and fluid). Observations of a single tsunami, with no subsequent waves, are consistent with our interpretation of landslide failure in a rapid, single phase of movement rather than a more piecemeal process, generating a tsunami which reached nearby coastlines within ~30 minutes. Both modelled rheologies successfully reproduce observed tsunami characteristics from post-event field survey results, tide gauge records, and eyewitness reports, suggesting our estimated landslide volume range is appropriate. This event highlights the significant hazard posed by relatively small-scale lateral volcanic collapses, which can occur en-masse, without any precursory signals, and are an efficient and unpredictable tsunami source. Our successful simulations demonstrate that current numerical models can accurately forecast tsunami hazards from these events. In cases such as Anak Krakatau’s, the absence of precursory warning signals together with the short travel time following tsunami initiation present a major challenge for mitigating tsunami coastal impact.