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Triggering factors, behavior, and social impact of the January 2021 hail-debris flows at the Central Valley of Chile
Abstract
Accepted paper
An extreme precipitation event produced catastrophic debris flows in central Chile during 29-31 January 2021 (austral summer). Our study focuses on the triggering factors and dynamic behavior of hail-debris flows affecting the small commune of Malloa (Central Valley), which caused 200 injured and 73 damaged houses. We carried out a post-event detailed field mapping of the local geology, the erosional features on the ravines, and its related hail-debris flow deposits. In parallel, the study involved a socio-cultural analysis of vulnerability to debris flows, with a particular focus on the disaster experience of the local community. Our results indicate that these hail-debris flows were likely conditioned by extended drought, local geomorphology, bedrock weathering/alteration, and water-oversaturated soil by two antecedent precipitation pulses. Soil erosion triggered by a hailstorm during a third precipitation pulse initiated hail-debris flows from small basins (<1.2 km2). Basin concentration times were estimated in 6-8 minutes, while hail reduced flow resistance by interparticle lubrication, promoting peak flow velocities near 2.4 to 5.5 m/s. Debris flow risk management should focus on developing suitable infrastructure and installing capacities at the local level as an essential condition for implementing subsequent inter-sectoral actions (for prevention, mitigation, and design risk scenarios).
... The emergence of lightning (Sup. Fig. 3) and the presence of hail on the ground (Romero et al., 2022) further supports the notion of strong convection developing in the evening of 30 and 31 January. To further quantify this aspect, Fig. 4d shows ERA5 hourly series of surface based Convective Available Potential Energy (CAPE) averaged over central Chile. ...
... Their temporal-latitudinal location is shown in Fig. 3a, revealing that most of the reported landslides occurred by the end of 30 and during 31 January between 33 and 35 • S (Metropolitan and O'Higgins regions), although more events may have occurred unreported in other sparsely populated Andean sectors. Romero et al. (2022) also describe a catastrophic hail-debris flow in isolated mountains of the central valley. The sudden increase in river flow and numerous landslides, in turn, caused dozens of roadblocks including cuts in two international routes and dozens of tourists stranded in the mountains for 3 days. ...
... Most of the landslides and flashfloods were trigger by high rain rates/hail in the COL-convective part of the storm (Fig. 3a) when the soil was already saturated -because of the ZAR precipitation (Romero et al., 2022). Furthermore, the extremely dry conditions that have prevailed in central Chile for more than a decade (the so-called Central Chile Mega Drought: Garreaud et al., 2017Garreaud et al., , 2019 has been suggested as a preconditioning element for the landslide generation (Romero et al., 2022) In this sense, the end of January 2021 storm can be framed as an extreme compound event (e.g., Leonard et al., 2014). ...
A major storm impacted the subtropical Andes during 28–31 January 2021 producing 4-days accumulated precipitation up to 100 mm over central-south Chile. These are high accumulations even for winter events but the storm occurred in the middle of the summer when precipitation in virtually absent, conferring it an extraordinary character. Similar storms have occurred only 2–3 times in the past century. The January 2021 event included periods of high rainfall intensity, hail and lighting, causing dozens of landslides and flash floods with the concomitant social impacts and economical losses. Here we examine the meteorological drivers of this storm at multiples scales, its climatological context, the associated surface impacts, and some aspects of its predictability.
About a week before the storm development over central Chile, a large-scale perturbation in the central South Pacific set the stage for the formation of a zonal jet aloft and zonal atmospheric river (ZAR) that extended eastward until reaching the west coast of South America. The ZAR landfalled at 39°S and its subsequent northward displacement resulted in copious orographic precipitation over the Andes and adjacent lowlands, concomitant with a relatively warm environment during first phase of the storm (28–29 January). During the second phase (30–31 January) the ZAR decayed rapidly but left behind significant amount of water vapor and the formation of a cut-off low (COL) in its poleward flank. The COL facilitated both advection of cyclonic vorticity and cold air at mid-levels, setting the environment for deep convection, intense rain showers, significant lightning activity, and hail.
An assessment of the quantitative precipitation forecast (QPF) from the operational Global Forecast System (GFS) indicates that the model captured well the 96-h precipitation accumulation (28–31 January) in terms of timing and spatial extent. However, specific zones with the largest accumulations varied as a function of lead time. The more stable precipitation during the ZAR phase was better predicted than the convective precipitation during the COL phase. Proper dissemination of these forecast and recently established infrastructure contributed to ease the impact of this extraordinary event on the general population.
A major storm impacted the subtropical Andes during 28-31 January 2021 producing 4-days accumulated precipitation up to 100 mm over central-south Chile. These are high accumulations even for winter events but the storm occurred in the middle of the
summer when precipitation in virtually absent, conferring it an extraordinary character.
Similar storms have occurred only 2-3 times in the past century. The January 2021 event included periods of high rainfall intensity, hail and lighting, causing dozens of landslides and flash floods with the concomitant social impacts and economical losses.
Here we examine the meteorological drivers of this storm at multiples scales, its climatological context, the associated surface impacts, and some aspects of its predictability.
About a week before the storm development over central Chile, a large-scale perturbation in the central South Pacific set the stage for the formation of a zonal jet aloft and zonal atmospheric river (ZAR) that extended eastward until reaching the west coast of South America. The ZAR landfalled at 39°S and its subsequent northward displacement resulted in copious orographic precipitation over the Andes and adjacent lowlands, concomitant with a relatively warm environment during first phase of the
storm (28-29 January). During the second phase (30-31 January) the ZAR decayed rapidly but left behind significant amount of water vapor and the formation of a cut-off low (COL) in its poleward flank. The COL facilitated both advection of cyclonic vorticity and cold air at mid-levels, setting the environment for deep convection, intense rain showers, significant lightning activity, and hail. An assessment of the quantitative precipitation forecast (QPF) from the operational Global Forecast System (GFS) indicates that the model captured well the 96-h precipitation accumulation (28-31 January) in terms of timing and spatial extent.
However, specific zones with the largest accumulations varied as a function of lead time. The more stable precipitation during the ZAR phase was better predicted than the convective precipitation during the COL phase. Proper dissemination of these forecast and recently established infrastructure contributed to ease the impact of this extraordinary event on the general population.
Debris flow generation in volcanic zones in the southern Andes has
not been widely studied, despite the enormous economic and infrastructure damage
that these events can generate. The present work contributes to the
understanding of these dynamics based on a study of the 2017 Petrohué
debris flow event from two complementary points of view. First, a
comprehensive field survey allowed us to determine that a rockfall initiated
the debris flow due to an intense rainfall event. The rockfall lithology
corresponds to lava blocks and autobrecciated lavas, predominantly over 1500 m a.s.l. Second, the process was numerically modelled and constrained by in
situ data collection and geomorphological mapping. The event was studied by
back analysis using the height of flow measured on Route CH-255 with errors
of 5 %. Debris flow volume has a high sensitivity with the initial water
content in the block fall zone, ranging from 4.7×105 up to
5.5×105 m3, depending on the digital elevation model (DEM) used.
Therefore, debris flow showed that the zone is controlled by the initial
water content available previous to the block fall. Moreover, our field data
suggest that future debris flows events can take place, removing material
from the volcanic edifice. We conclude that similar events could occur in
the future and that it is necessary to increase the mapping of zones with
autobrecciated lava close to the volcano summit. The study contributes to
the understanding of debris flows in the southern Andes since the Osorno volcano
shares similar features with other stratovolcanoes in the region.
Piton de la Fournaise (PdF) is a basaltic volcano whose activity is characterized by effusive to mildly explosive eruptions. The geologic record preserves evidence of explosive eruptions associated with the seaward sliding of the steep east flank. Such eruptions formed calderas that are several km in diameter and their products have been emplaced as breccias. The breccias of PdF offer the opportunity to sample a wide range of different lithologies covering most of the stratigraphy of the edifice. Petrophysical measurements revealed a corresponding variability in density, porosity, P-wave velocity, and uniaxial compressive strength, confirming the petrophysical consequences of the lithological diversity. Different lithologies cannot simply be distinguished on the basis of their physical properties. We infer that volcano instability should not be interpreted solely in terms of altered rock units. The large heterogeneity of crustal rocks must be considered when interpreting monitoring data and assessing hazards related to volcano stability.
Hail impact-induced erosion has the potential to significantly affect the operational lifetime of structures exposed to extreme weathering environments such as hail events. Computational materials modelling can be used to better understand the erosion behaviour during a hailstone impact, and here the relevant background work is detailed. In this paper, an implementation of an ice impact model, utilising Smooth Particle Hydrodynamics along with a highly strain-rate-dependent material model, is shown, and its results and limitations discussed. An overview is given on the literature on modelling hail events, including the history of experimental work. The various potential modelling methods which have been developed is then given, along with an evaluation of the suitability of the methods to future work in this area.
Sangay is one of the most active volcanoes in the world. Its eruptions were first recorded by Spanish priests in 1628, and since 2010 it has displayed VEI 1–2 level eruptive activity about every two years. Its most recent eruptive phase began on May 7, 2019, and has continued until the present. While most eruptive products do not impact inhabited areas, Sangay's associated Pleistocene-age avalanche deposits were enormous and far-reaching. Their surfaces are now populated by numerous communities on the volcano's E and SE aprons. The study of Sangay's debris-avalanche deposits located in SE Ecuador in the upper Amazon Basin indicates at least two avalanche events. Sangay Debris Avalanche-1 is the first deposit (250–100 Ka, as reported by Monzier et al., 1999), and Sangay Debris Avalanche-2 the younger deposit (~30 Ka, ¹⁴C dated). Both avalanches have a run-out distance of more than 60 km from Sangay's central crater. Statistical analysis of 541 counted hummocks shows that the largest hummocks are located in the middle run-out zone, between 40 and 50 km from the volcano. This middle zone possibly indicates that while in transport, the younger avalanche impacted laterally with a 500 m high ridge located SE of the volcano. The flow was redirected around this elevated, uplifted morphology. Petrological and geochemical data of clasts from the avalanche deposits have a similar affinity with late Holocene primary eruptive products from Sangay volcano. The vertical relief, mapped area, run-out distance, and the estimated deposit volumes categorize the two Sangay debris avalanche deposits as some of the furthest reaching volcanic slides related to continental volcanoes. Numerical simulations indicate that Sangay's potential future flank collapse could produce large debris avalanche deposits directed to the East, occupying the northern and southern drainage networks around the volcano. Several localities and towns would be affected, and the flow of major rivers would be blocked, and subsequent secondary lahars could have important discharges (1000 to 10,000 m³/s). We performed numerical simulations using the VolcFlow code, applying rheological parameters (plastic retarding stress of ~50 kPa) to simulate possible future debris avalanches of Sangay volcano.
The interpretation of disaster through a religious lens has produced diverse theological perspectives regarding the disaster. This article seeks to analyze the theology of disaster from a Protestant perspective, which may be combined with local knowledge and modern science to create disaster response strategies. This study is based on field studies and related literature analysis with a qualitative method using an ethnoscience approach to see disaster phenomena in the context of Indonesian society, using primary data and secondary data. This study finds out that within Christian theology and among its follower's disasters can be seen as the means through which God glorifies His creation while punishing those who have sinned and abandoned His teachings. It concludes, first, that God-the Creator-shows His love and mercy even through a disaster. In the Protestant perspective, God seeks to honor His creation by mercifully creating balance. Second, disaster, as part of a natural cycle, should also be understood through local knowledge and modern science; as such, a holistic approach is necessary to understand and respond to a disaster.
Whether arc magmatism occurs above oceanic subduction zones is the forefront of studies on convergent plate margins. The most important petrologic issue related to the evolution of arc systems is the origin of arc magmatism, among which arc basalts are the most important one because they provide insights into mantle enrichment mechanism and crust-mantle interaction at oceanic subduction zones. Fluids or melts released either by dehydration or by melting of subducting oceanic slab infiltrate and metasomatize the overlying mantle wedge at varying depth, leading to the formation of source regions of arc basalts. Such processes make most of arc basalts commonly enriched in large ion lithosphile elements and light rare earth elements, but depleted in high-field strength elements and heavy rare earth elements. Small amounts of arc basalts are characterized by relatively high Nb contents or by Nb enrichment. Rare basalts with compositions similar to ocean island basalts or mid-ocean ridge basalt also occur in arc systems. For these peculiar rocks, it remains debated whether their source is affected by subduction-related components. During their ascent and before their eruption, arc basaltic magmas are subjected to crystal fractionation, mixing and crustal contamination. In addition to the contribution of subducting slab components to the mantle source of arc basalts, the materials above the subducting slab at forearc depths would have been transported either by drag or by subduction erosion into the subarc mantle and into the source of arc magmas. Heats and materials brought by corner flows also play important roles in the generation of arc basalts. Despite the important progresses made in recent studies of arc basalts, further efforts are needed to investigate subarc mantle metasomatism, material recycling, the formation of arc magma sources, geodynamic mechanism in generating arc basalts, and their implicationd s for the initiation of plate tectonics on Earth.
The evolution of complex volcanic structures usually includes the occurrence of flank collapse events. Monogenetic cones, however, are more stable edifices with minor rafting processes that remove part of the cone slopes. We present the eruptive history of Mazo volcano (Lanzarote, Canary Islands), including the first detailed description of a syn-eruptive debris avalanche affecting a volcanic monogenetic edifice. The study and characterization, through new geological and morphological data and the analysis of a great number of documentary data, have made it possible to reinterpret this volcano and assign it to the Timanfaya eruption (1730–1736). The eruptive style evolved from Hawaiian to Strombolian until a flank collapse occurred, destroying a great part of the edifice, and forming a debris avalanche exhibiting all the features that define collapsing volcanic structures. The existence of blocks from the substrate suggests a volcano-tectonic process associated with a fracture acting simultaneously with the eruption. The sudden decompression caused a blast that produced pyroclasts that covered most of the island. This study forces to change the current low-hazard perception usually linked to monogenetic eruptions and provides a new eruptive scenario to be considered in volcanic hazards analysis and mitigation strategies development.
The estimation of the volume of volcanic flows during an ongoing eruption is challenging but this information is crucial for improving risk assessment and for forecasting future events. Although previous studies have shown the ability of TanDEM-X satellite data to derive the thickness and the volume of lava flow fields during effusive eruptions, the method has not been explored yet for pyroclastic flows. Using bi-static interferometry, we produce TanDEM-X DEM on Fuego volcano (Guatemala) to measure the significant topographic changes caused by the 3rd June 2018 eruption, which destroyed the town of San Miguel Los Lotes. We estimate the volume of the Pyroclastic Density Currents (PDCs) to be 15.1 ± 4.2 × 106 m3. The deposits are likely to be the source of lahars during future rainy seasons. We identify the main channel of deposition (positive elevation changes) and the source region of pyroclastic material, areas of significant substrate erosion, and vegetation destruction (negative elevation changes). Our results show that the June 3rd 2018 pyroclastic flow was predominantly composed of material which had gravitationally collapsed from a location close to the vent. The eroded material increased the volume of the flow (bulking) and likely caused the run-out distance of the 2018 PDC to be larger than previous eruptions (1999–2017). This study highlights the potential of remote sensing techniques for actively monitoring topography changes in inaccessible locations and to rapidly derive deposit volumes.
In active volcanic arcs such as the Andean volcanic mountain belt, magmatically-sourced fluids are channelled through the brittle crust by faults and fracture networks. In the Andes, volcanoes, geothermal springs and major mineral deposits have a spatial and genetic relationship with NNE-trending, margin-parallel faults and margin-oblique, NW-trending Andean Transverse Faults (ATF). The Tinguiririca and Planchón-Peteroa volcanoes in the Andean Southern Volcanic Zone (SVZ) demonstrate this relationship, as their spatially associated thermal springs show strike alignment to the NNE-oriented El Fierro Thrust Fault System. We constrain the fault system architecture and its interaction with volcanically sourced hydrothermal fluids using a combined magnetotelluric (MT) and seismic survey that was deployed for 20 months. High conductivity zones are located along the axis of the active volcanic chain, delineating fluids and/or melt. A distinct WNW-trending cluster of seismicity correlates with resistivity contrasts, considered to be a reactivated ATF. Seismicity occurs below 4 km, suggesting activity is limited to basement rocks, and the cessation of seismicity at 9 km delineates the local brittle-ductile transition. As seismicity is not seen west of the El Fierro fault, we hypothesize that this structure plays a key role in compartmentalizing magmatically-derived hydrothermal fluids to the east, where the fault zone acts as a barrier to cross-fault fluid migration and channels fault-parallel fluid flow to the surface from depth.
Increases in fluid pressure above hydrostatic may facilitate reactivation. This site-specific case study provides the first three-dimensional seismic and magnetotelluric observations of the mechanics behind the reactivation of an ATF.
Over the past decades, several numerical models have been developed to understand, simulate and predict debris flow events. Typically, these models simplify the complex interactions between water and solids using a single-phase approach and different rheological models to represent flow resistance. In this study, we perform a sensitivity analysis on the parameters of a debris flow numerical model (FLO-2D) for a suite of relevant variables (i.e., maximum flood area, maximum flow velocity, maximum height and deposit volume). Our aims are to (i) examine the degree of model overparameterization and (ii) assess the effectiveness of observational constraints to improve parameter identifiability. We use the Distributed Evaluation of Local Sensitivity Analysis (DELSA) method, which is a hybrid local-global technique. Specifically, we analyze two creeks in northern Chile (∼ 29 • S, 70 • W) that were affected by debris flows on 25 March 2015. Our results show that SD (sur-face detention) and β 1 (a parameter related to viscosity) provide the largest sensitivities. Further, our results demonstrate that equifinality is present in FLO-2D and that the final deposited volume and maximum flood area contain considerable information to identify model parameters.
The contribution of an individual extreme storm event to long-term erosion rates has been estimated for the first time in the Atacama Desert. A mean erosion of 1.3 mm has been calculated for the March 2015 event that impacted the southernmost part of the Atacama Desert. The estimated erosion is consistent with millennial erosion rates and the previously reported return times of high-sediment-discharge events in the study area. This is significant because erosion rates, related to events of high sediment discharge in arid fluvial systems, are difficult to measure with sediment loading due to destruction of gauges by devastating flash floods and therefore have not been directly measured yet. During the March 2015 storm, debris flows were reported as the main sediment transport process, while gullies and channels erosion were the main source of sediments that generated debris flows reaching the tributary junctions and the trunk valleys. Sediment yield at tributary outlets is highly dependent on the ability of catchments to store sediments in stream networks between storms. The largest tributary catchments, the high hydrological hierarchy, the low topographic gradient and the gentle slopes are the most determining factors in generating debris flows capable of reaching alluvial fans in any storm event from large sediment volumes stored in the stream networks. Our findings better assess the susceptibility to debris flow of arid catchments, which is significant for the southernmost valleys of the Atacama Desert because human settlements and industries are mostly established in alluvial fans.
The May 2018 rift intrusion and eruption of Kīlauea Volcano, Hawai‘i, represented one of its most extraordinary eruptive sequences in at least 200 years, yet the trigger mechanism remains elusive¹. The event was preceded by several months of anomalously high precipitation. It has been proposed that rainfall can modulate shallow volcanic activity2,3, but it remains unknown whether it can have impacts at the greater depths associated with magma transport. Here we show that immediately before and during the eruption, infiltration of rainfall into Kīlauea Volcano’s subsurface increased pore pressure at depths of 1 to 3 kilometres by 0.1 to 1 kilopascals, to its highest pressure in almost 50 years. We propose that weakening and mechanical failure of the edifice was driven by changes in pore pressure within the rift zone, prompting opportunistic dyke intrusion and ultimately facilitating the eruption. A precipitation-induced eruption trigger is consistent with the lack of precursory summit inflation, showing that this intrusion—unlike others—was not caused by the forceful intrusion of new magma into the rift zone. Moreover, statistical analysis of historic eruption occurrence suggests that rainfall patterns contribute substantially to the timing and frequency of Kīlauea’s eruptions and intrusions. Thus, volcanic activity can be modulated by extreme rainfall triggering edifice rock failure—a factor that should be considered when assessing volcanic hazards. Notably, the increasingly extreme weather patterns associated with ongoing anthropogenic climate change could increase the potential for rainfall-triggered volcanic phenomena worldwide.
Magmatic intrusions, eruptions and flank collapses are frequent processes of volcano dynamics, inter-connected at different space and time scales. The December 2018 recrudescent episode at Mt. Etna is an exemplary case where a sudden intrusive event culminated with a short eruption, intense seismicity and a shallow large strike-slip earthquake at the edge of the eastern sliding flank. Here, we show that high resolution velocity models and transient changes of VP and VP/VS resolve the magma intrusion through a dyke and local stress increase at the base of the unstable flank, inducing the collapse. Episodic brittle faulting occurs at the edge of the sliding sector, locally contributed by high fluid pressure. The feedback between magma ascent, stress changes and flank collapse is driving the volcano dynamics, with processes ranging from long term to transient episodes.
High rates of volcano surface deformation can be indicative of a forthcoming eruption, but can also relate to slope instability and possible flank collapse. Tungurahua volcano, Ecuador, has been persistently active since 1999 and has previously experienced catastrophic flank failures. During the ongoing eruptive activity, significant surface deformation has been observed, with the highest rates contained within the amphitheatre-shaped scar from the 3000-year-old failure on the west flank. However, the cause of this asymmetric deformation and how it might relate to slope stability has not been assessed. Here, for the first time, we present a range of models to test physical processes that might produce asymmetric deformation, which are then applied to slope stability. Our models are informed by InSAR measurements of a deformation episode in November 2015, which show a maximum displacement of ∼3.5 cm over a period of ∼3 weeks, during which time the volcano also experienced multiple explosions and heightened seismicity. Asymmetric flank material properties, from the rebuilding of the cone, cannot explain the full magnitude and spatial footprint of the observed west flank deformation. The inflation is inferred to be primarily caused by shallow, short-term, pre-eruptive magma storage that preferentially exploits the 3 ka flank collapse surface. Shallow and rapid pressurization from this inclined deformation source can generate shear stress along the collapse surface, which increases with greater volumes of magma. This may contribute to slope instability during future unrest episodes and promote flank failure, with general application to other volcanoes worldwide displaying asymmetric deformation patterns.
Volcanic archipelagos are a source of numerous on- and offshore geohazards, including explosive eruptions and potentially tsunamigenic large-scale flank-collapses. Fogo Island in the southern Cape Verdes is one of the most active volcanoes in the world, making it both prone to collapse (as evidenced by the ca. 73 ka Monte Amarelo volcanic flank-collapse), and a source of widely-distributed tephra and volcanic material. The offshore distribution of the Monte Amarelo debris avalanche deposits and the surrounding volcaniclastic apron were previously mapped using only medium-resolution bathymetric data. Here, using recently acquired, higher resolution acoustic data, we revisit Fogo’s flank-collapse, and find evidence suggesting that the deposition of hummocky volcanic debris originating from the failed eastern flank most likely triggered the contemporaneous, multi-phase failure of pre-existing seafloor sediments. Additionally, we identify, for the first time, multiple mass-transport deposits in the southern part of the volcaniclastic apron of Fogo and Santiago based on the presence of acoustically chaotic deposits in parametric echo sounder data and volcaniclastic turbiditic sands in recovered cores. These preliminary findings indicate a long and complex history of instability on the southern slopes of Fogo and suggest that Fogo may have experienced multiple flank collapses.
Basaltic eruptions are the most common form of volcanism on Earth and planetary bodies. The low viscosity of basaltic magmas inhibits fragmentation, which favours effusive and lava-fountaining activity, yet highly explosive, hazardous basaltic eruptions occur. The processes that promote fragmentation of basaltic magma remain unclear and are subject to debate. Here we used a numerical conduit model to show that a rapid magma ascent during explosive eruptions produces a large undercooling. In situ experiments revealed that undercooling drives exceptionally rapid (in minutes) crystallization, which induces a step change in viscosity that triggers magma fragmentation. The experimentally produced textures are consistent with basaltic Plinian eruption products. We applied a numerical model to investigate basaltic magma fragmentation over a wide parameter space and found that all basaltic volcanoes have the potential to produce highly explosive eruptions. The critical requirements are initial magma temperatures lower than 1,100 °C to reach a syn-eruptive crystal content of over 30 vol%, and thus a magma viscosity around 10⁵ Pa s, which our results suggest is the minimum viscosity required for the fragmentation of fast ascending basaltic magmas. These temperature, crystal content and viscosity requirements reveal how typically effusive basaltic volcanoes can produce unexpected highly explosive and hazardous eruptions.
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.
Groups defined by race and ideology are well‐known predictors of interpersonal and political trust, but gender‐based effects are undecided. I investigate whether disaster experience conditions a difference in political trust between women and men. Examining the hurricane data set of U.S. public opinion, I analyze intersectionality's influence on disaster‐based political trust with a three‐way interaction between race, class, and gender. Among disaster survivors, black women trust less than all other race–gender groups, and white men trust the most. The difference between black and white women survivors’ political trust is attenuated by education. Education exacerbates race‐based political trust among observers. Among observers, there is not a gender‐based distinction. Disasters create new identities based on shared experience, and offer a moment in time that illustrates how trust varies along gender–race–class–disaster dimensions. Knowing how trust differs according to intersectionality allows managers to manage critical events better.
We have calculated a mean erosion of 1.3 mm caused by an individual storm event in March 2015 that impacted a large mountainous area of the southernmost Atacama Desert. The calculated erosion agrees with millennial erosion rates and with return time of high sediment discharge events previously reported in the study area. Here, we quantify for the first time the contribution of an individual extreme storm event to long-term erosion rates in the Atacama Desert. This is significant because erosion rates, related to high sediment discharge events in arid fluvial systems, are hard to measure with sediment load due the destruction of gauges by devastating flashfloods and thus have not been directly measured yet. During the March 2015 storm, debris flows were reported as the main sediment transport process. Erosion of gullies and channels are the main source of sediments that finally generate debris flows that reach the tributary junctions and the trunk valleys. The sediment yield to the tributary outlets strongly depends on the hydraulic capacity of catchments to store sediments in the drainage network between storms. Larger tributary catchments, high hydrological hierarchy, low topographic gradient and gentle slopes are the most susceptible catchments to generate debris flows that reach alluvial fans at any storm event from large debris volumes stored in the drainage network. Our findings better assess debris flow susceptibility of arid catchments, which is significant for the southernmost Atacama Desert valleys because human settlements and industries are mostly established in alluvial fans.
Extreme rainfall events are thought to be one of the major threats of climate change given an increase of water vapor available in the atmosphere. However, before projecting future changes in extreme rainfall events, it is mandatory to know current patterns. In this study we explore extreme daily rainfall events along central-southern Chile with emphasis in their spatial distribution and concurrent synoptic-scale circulation. Surface rain gauges and reanalysis products from the Climate Forecast System Reanalysis are employed to unravel the dependency between extreme rainfall and horizontal water vapor fluxes. Results indicate that extreme rainfall events can occur everywhere, from the subtropical to extratropical latitudes, but their frequency increases where terrain has higher altitude, especially over the Andes Mountains. The majority of these events concentrate in austral winter, last a single day, and encompass a north–south band of about 200 km in length. Composited synoptic analyses identified extreme rainfall cases dominated by northwesterly (NW) and westerly (W) moisture fluxes. Some features of the NW group include a 300-hPa trough projecting from the extratropics to subtropics, a surface-level depression, and cyclonic winds at 850 hPa along the coast associated with integrated water vapor (IWV) > 30 mm. Conversely, features in the W group include both a very weak 300-hPa trough and surface depression, as well as coastal westerly winds associated with IWV > 30 mm. About half of extreme daily rainfall is associated with an atmospheric river. Extreme rainfall observed in W (NW) cases has a strong orographic (synoptic) forcing. In addition, W cases are, on average, warmer than NW cases, leading to an amplified hydrological response.
Central Chile, along the subtropical west coast of South America, has experienced an uninterrupted sequence of dry winters (annual rainfall deficit 20-40%) since 2010. The so called Mega Drought (MD) is the longest event on record and encompasses a broad area, with detrimental effects on water availability, vegetation and forest fires. Local records and reanalysis data reveal that the exceptional length of the MD results from the reiteration of a circulation dipole -disfavoring the passage of extratropical storms over central Chile- characterized by troposheric-deep positive pressure anomalies over the southeast subtropical Pacific and negative pressure anomalies over the Amundsen-Bellinhausen Sea. Historically, ENSO is a major modulator of such dipole, but the ongoing dry period has occurred under ENSO-neutral conditions, except for the winters of 2010 (La Niña) and 2015 (strong El Niño). Nonetheless, atmospheric-only global model simulations forced with observed global SST and present-day radiative forcing replicate the south Pacific dipole and capture part of the rainfall anomalies during the MD. Further numerical experiments suggest that most of the ocean forcing emanates from the subtropical southwest Pacific, a region that has experienced a marked warming over the last decade. Such warming may excite Rossby waves whose propagation intensify the circulation pattern that lead to dry conditions in central Chile. On the other hand, the positive trend of the Southern Annular Mode also contributes to strength of the south Pacific dipole, signaling that anthropogenic forcing (greenhouse gases concentration increase and stratospheric ozone depletion) have played a role on the maintenance of the central Chile MD. Given the concomitance of natural (ocean sourced) and anthropogenic forcing, we anticipate only a partial recovery of central Chile precipitation in the decades to come.
Central Chile, home to more than 10 million inhabitants, has experienced an uninterrupted sequence of dry years since 2010 with mean rainfall deficits of 20–40%. The so-called Mega Drought (MD) is the longest event on record and with few analogues in the last millennia. It encompasses a broad area, with detrimental effects on water availability, vegetation and forest fires that have scaled into social and economical impacts. Observations and reanalysis data reveal that the exceptional length of the MD results from the prevalence of a circulation dipole-hindering the passage of extratropical storms over central Chile—characterized by deep tropospheric anticyclonic anomalies over the subtropical Pacific and cyclonic anomalies over the Amundsen–Bellingshausen Sea. El Niño Southern Oscillation (ENSO) is a major modulator of such dipole, but the MD has occurred mostly under ENSO-neutral conditions, except for the winters of 2010 (La Niña) and 2015 (strong El Niño). Climate model simulations driven both with historical forcing (natural and anthropogenic) and observed global SST replicate the south Pacific dipole and capture part of the rainfall anomalies. Idealized numerical experiments suggest that most of the atmospheric anomalies emanate from the subtropical southwest Pacific, a region that has experienced a marked surface warming over the last decade. Such warming may excite atmospheric Rossby waves whose propagation intensifies the circulation pattern leading to dry conditions in central Chile. On the other hand, anthropogenic forcing (greenhouse gases concentration increase and stratospheric ozone depletion) and the associated positive trend of the Southern Annular Mode also contribute to the strength of the south Pacific dipole and hence to the intensity and longevity of the MD. Given the concomitance of the seemingly natural (ocean sourced) and anthropogenic forcing, we anticipate only a partial recovery of central Chile precipitation in the decades to come.
Long-lived, high-angle fault systems constitute high-permeability zones that can localize the upward flow of hydrothermal fluids and magma throughout the upper crust. Intersections of these types of structures can develop complex interference patterns, which constitute volumes of damaged rock (networks of small-scale faults and fractures) where permeability may be significantly enhanced. This is relevant for understanding regional-scale structural controls on the emplacement of hydrothermal mineral deposits and volcanic centers, and also on the distribution of areas of active upper-crustal seismicity. In the high Andes of central Chile, regional-scale geophysical (magnetic, gravimetric, seismic) and structural datasets demonstrate that the architecture of this Andean segment is defined by NW-and NE-striking fault systems, oblique to the N-S trend of the magmatic arc. Fault systems with the same orientations are well developed in the basement of the Andes. The intersections of conjugate arc-oblique faults constitute the site of emplacement of Neogene intrusive complexes and giant porphyry Cu-Mo deposits, and define the location of major clusters of upper-crustal earthquakes and active volcanic centers, suggesting that these fault systems are still being reactivated under the current stress regime. A proper identification of one-dimensional, lithospheric-scale high-permeability zones located at the intersections of high-angle, arc-transverse fault systems could be the key to understanding problems such as the structural controls on magmatic and hydrothermal activity and the patterns of upper-crustal seismicity in the high Andes and similar orogenic belts. Keywords: Basement fault intersections, Magma and hydrothermal fluid flow, Central Chile.
Over 2 weeks in August 2014, magma propagated 48 km laterally from Bárðarbunga volcano before erupting at Holuhraun for 6 months, accompanied by collapse of the caldera. A dense seismic network recorded over 47,000 earthquakes before, during, and after the rifting event. More than 30,000 earthquakes delineate the segmented dike intrusion. Earthquake source mechanisms show exclusively strike‐slip faulting, occurring near the base of the dike along preexisting weaknesses aligned with the rift fabric, while the dike widened largely aseismically. The slip sense of faulting is controlled by the orientation of the dike relative to the local rift fabric, demonstrated by an abrupt change from right‐ to left‐lateral faulting as the dike turns to propagate from an easterly to a northerly direction. Around 4,000 earthquakes associated with the caldera collapse delineate an inner caldera fault zone, with good correlation to geodetic observations. Caldera subsidence was largely aseismic, with seismicity accounting for 10% or less of the geodetic moment. Approximately 90% of the seismic moment release occurred on the northern rim, suggesting an asymmetric collapse. Well‐constrained focal mechanisms reveal subvertical arrays of normal faults, with fault planes dipping inward at ∼60° ± 9°, along both the north and south caldera margins. These steep normal faults strike subparallel to the caldera rims, with slip vectors pointing toward the center of subsidence. The maximum depth of seismicity defines the base of the seismogenic crust under Bárðarbunga as 6 km below sea level, in broad agreement with constraints from geodesy and geobarometry for the minimum depth to the melt storage region.
Cryptodomes are shallow-level intrusions that cause updoming of overlying sediments or other rocks. Understanding the formation of cryptodomes is important for hazard assessment, as cryptodome-forming eruptions are one of the major triggering factors in sector collapse. This paper describes internal structures of a Quaternary subaerial rhyodacite cryptodome at Ogariyama, Usu volcano, Japan (the Ogariyama dome), and examines the textural differences between subaerial and subaqueous cryptodomes to extend our knowledge of these phenomenon. The Ogariyama dome, which is one of the youngest subaerial cryptodomes in the world (<0.4 ka), can be viewed in cross-section because a vertical fault formed during the 1977–1978 eruption and cut through the center of the cryptodome, exposing its interior. The morphology of the cryptodome is scalene triangular in shape, with rounded corners in cross-section, and it is 150 m across and 80 m high. The internal structure of the dome is concentrically zoned, with a massive core, jointed rim, and brecciated border, all of which are composed of uniform, feldspar-phyric rhyodacite (SiO2 = 71–72 wt.%). The massive core (130 m across) consists of coherent rhyodacite that has indistinct, large-scale flow banding and rectangular joints that are spaced 50–200 cm apart. The jointed rim (8–12 m wide) surrounds the massive core and consists of coherent rhyodacite that is characterized by distinct rectangular joints that are 30–80 cm apart and radiate outward. The outermost brecciated border (7–10 m wide) comprises monolithological breccia, consisting of angular rhyodacite clasts (5–30 cm across) and a cogenetic matrix. These internal structures suggest that the Ogariyama dome was formed by endogenous growth, involving continuous magma supply during a single intrusive event and simple expansion from its interior. The massive core formed by slow cooling of homogeneous rhyodacite magma. The jointed rim formed by fracturing of solidifying rhyodacite magma in response to cooling–contraction and dynamic stress driven by continued movement of the less viscous core. The brecciated border formed by fragmentation of the solidified rim of the dome in response to dynamic stress. The growth style of the Ogariyama dome closely resembles that of subaqueous cryptodomes. However, the morphology and internal structures of the Ogariyama dome differ from those of subaqueous cryptodomes, given its asymmetric morphology and absence of radial columnar joints and large-scale flow banding. These differences might reflect the well-consolidated and inhomogeneous physical properties of the host sediment and the slow cooling rate and high viscosity of the Ogariyama dome. The Ogariyama dome is probably the best cross-sectional example of a subaerial cryptodome in the world. Our descriptive study of the cryptodome provides invaluable information for hazard assessment.
Discourses in disaster studies have seen a paradigm shift from hazard centric to people focussed approaches. ‘Social vulnerability’ has been the key to understanding experiences of people and communities with respect to disasters. Through a narrative ethnographic study of the Nepal earthquake in 2015, this study aims to understand post‐disaster experiences of relief and rehabilitation of Nepali women. In doing so, it adopts an intersectional approach to vulnerability and privileges voices of marginalized women in post disaster contexts.
This paper brings out narratives of violent experiences in post disaster spaces which include stories of rampant alcoholism, drug abuse, illegal trafficking, prostitution, self‐harm and suicides. These violent experiences are more pronounced in the voices of Dalit women who also face institutionalized violence in the form of unequal access to disaster relief aid, dignity kits, safe spaces, among other resources. Such discrimination makes Dalit women from poor socio‐economic backgrounds more vulnerable in post disaster contexts. In the case of Nepal, relief and rehabilitation processes carried out by the Government, Army and NGOs, failed to understand and address intersectional vulnerability and in some respect became part of the problem. Therefore, through examining narratives of women across different caste and class, this paper argues for an intersectional approach to examining vulnerability in post disaster contexts.
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Volcanic landslides are controlled by a combination of magmatic, tectonic and surficial processes, the last of which is predominantly influenced by climate. In this chapter, we consider the influences of present and geologically recent climates on the occurrence of volcanic landslides. We begin by summarizing Quaternary climatic variability to illustrate the wide range of conditions and rates of change experienced by modern edifices. A focus on geologically recent volcanoes is prudent because both their morphologies and evidence of the climatic conditions affecting them are typically better preserved; pre-Quaternary climates similarly affected edifices that are now largely lost from the geomorphic record. We then review the climatic factors that condition and possibly trigger volcanic landslides, the challenges in dating landslides and climatic changes, and the difficulties in determining triggers of volcanic landslides. Finally, case studies of present and past climate influences on volcanic landslides collected from scientific literature–covering both subaerial and coastal settings–illustrate several key points: edifice collapses were numerous at the end of the last glaciation; current glacial retreat is conditioning volcanic slope failure in some specific settings; shallow landslides in volcanic environments appear to be increasing due to changes in weather extremes; and sea level fluctuation plays a role in volcanic island collapses. As knowledge on climate variability, volcanic, and surficial processes progresses, the understanding of how climate and its changes affect volcanic landslides will further improve.
In the four decades since the 1980 eruption of Mount St. Helens, debris-avalanche deposits generated by gravitational lateral collapse of volcanoes have become widely recognized. Selected regionally sequenced case studies highlight the evolution of thought regarding these events prior to 1980 in contrast to subsequent research with benefit of insights from the events of May 18, 1980. These typically hummocky deposits, of volcanic materials but lying far beyond volcanoes, had puzzled geologists for more than a century and been interpreted as a wide range of primary and secondary volcanic or non-volcanic features. Contrary to general perception, however, the volcanological literature contained multiple accounts prior to 1980 that recognized the landslide origin of some of these deposits, albeit mostly in regional publications not widely known. The burst of interest in lateral-collapse events after 1980 has led to an average of one regional or global debris-avalanche inventory annually in terrestrial or submarine settings and the recognition of a thousand events from nearly 600 volcanoes. The last major volcaniclastic process to be widely recognized and understood, large-volume debris avalanches originating from lateral collapse of volcanic edifices have been found to be a relatively common occurrence across a wide spectrum of volcanic features and settings.
Many factors can lead to volcano lateral collapse, which can produce devastating debris avalanches that travel up to several tens to over 100 km and cover hundreds to more than a thousand km 2 with debris. Volcanic lateral collapses are severe hazards because of their destructive power and size, and sudden onset. Although their frequency of occurrence is not as high as those of smaller volcanic mass movements, such as rock falls and lahars, globally large collapses ! 0.1 km 3 have occurred at least five times per century over the last 500 years. A large variety of destabilizing factors such as over-steepened slopes, magma intrusions, hydrothermal activity , climate fluctuations, deformation of the basement, and faulting can create the conditions for volcano collapse. Once a volcano reaches its critical point, a mechanism is necessary to trigger the failure event. We present the state-of-the-art of the knowledge acquired in the last few decades concerning the causes of large-scale volcanic failures to better understand the triggers, preparatory factors, and timing of volcano lateral collapse.
The March 2015 extraordinary hydrometeorological event in the Andes cordillera caused severe floods in the southern Atacama Desert. One of the most affected cities was Copiapó (northern Chile) located at the downstream the junction between the Copiapó river and its ephemeral tributary Quebrada Paipote. This work analyses the features of this catastrophic flood and relate them with the identified impacts. A large volume of water mixed with fine sediments overflowed the tributary channel generating a flood that affected 72% of the urban area. The rheological (velocity, density and flow regime) and sedimentary features of the flow reveal the occurrence of massive mudflows that infilled the space available inside the buildings, buried the streets with a sandy mud deposit of more than 30 cm medium thickness and made the sewer network to collapse. The post-event survey carried out by the Ministry of Housing and Urban Planning (MINVU) was used for the development of fragility curves that allows modelling the probability of damage. Results indicate that the greatest probability of building damage is generated by the accumulation of sediments instead of the flow depth. On the other hand, once the very fine grain sediments of the top of the deposit dried up it increased the concentration of post-event suspension particulate matter causing a health issue. This work highlights the need to understand mudflow processes and their consequences in arid environments to improve urban planning and mitigate future damages since their impacts strongly affect infrastructures and communities.
In continental arcs, the exposure of primitive eruptive products at the surface is typically a result of rapid magmatic transfer through the crust. As a result, the initially primitive magma experiences minimal crustal residence and thus insignificant differentiation towards more evolved products. This rapid transfer of primitive magma through thickened crust is commonly recorded from smaller, monogenetic cinder cones. Manantial Pelado (35.5°S) is a long-lived stratocone in the Southern Andean Volcanic Zone (SVZ) overlying thick continental crust (45-50 km) that produces almost exclusively mafic material. As Manantial Pelado is surrounded by extensive silicic volcanism, the study of its mafic exposure as a stratocone can be used to further understand magmatic origins of long-lived volcanic systems. Our study uses textural, geochemical, and geochronological data from lavas collected from Manantial Pelado to characterize its magmatic petrogenesis, assess the primitive nature, and explain processes in the crust within the SVZ. A geologic description of the volcano reveals a mostly monotonous eruptive history of basaltic andesites that are now accessible through glacially carved valleys. New 40 Ar/ 39 Ar dating constrains most of the volcano's cone constructing phase to last from~220 to 190 ka. At~30 ka, small-volume activity and different petrography of more intermediate magmas were present reflecting a change in the volcano's character. A combination of the whole-rock and mineral-scale data reveals that basaltic andesites at Manantial Pelado are among the most primitive magmas in the thickened crust of the SVZ. Evidence for this primitive signature consists of textural and zonation patterns in olivine, the presence of Cr-spinel in olivine cores, and elevated Fo and Ni content within olivine cores. This data combined with elemental diffusion modeling provides evidence for a primitive signature for these lavas. Intermediate Fo olivines with uniform core compositions (Fo 80-84) suggest that basaltic andesites reside in the crust in quasi-closed system environments for extended storage prior to eruption (2 5-6000 years). Diffusive equilibration in those intermediate Fo olivines masks the primitive nature of the magmas. These results suggest that mafic magmas can have a protracted storage history in the crust that does not significantly alter their primitive bulk composition before reaching the surface. We argue that these are important processes in understanding the magmatic origin of long-lived systems and the presence of compositionally homogenous olivines at intermediate Fo content may represent cryptic evidence for recharge with primitive magmas that experienced prolonged crustal storage.
Over the past decades, many numerical models have been developed to understand, simulate and predict debris flow processes. Typically, these models simplify the complex interactions between water and solids using a single phase approach and different rheological models to represent flow resistance. Further, different rheological models have different sets of uncertain parameters that need to be specified to simulate debris flow. In this study, we perform a sensitivity analysis for a debris flow numerical model (FLO-2D) to identify the most sensitive parameters for a suite of relevant simulated variables (i.e., run-out distance, maximum flow velocity, minimum flow velocity, deposit depth). We use the Distributed Evaluation of Local Sensitivity Analysis (DELSA) method, which is a hybrid local-global technique. Specifically, we analyze the debris flow event occurred in northern Chile on March 25, 2015. We include two different ravine types: (i) La Mesilla ravine, characterized by a big alluvial fan where considerable sedimentation occurs, and (ii) Acerillas ravine, characterized by a marked narrow channel with almost none alluvial fan, where sediments are mainly transported to the river. We apply the DELSA method for the above ravines, considering eight FLO-2D parameters used to estimate the friction factor. We also examine the influence of topography and grid cell size on parameter sensitivities. Our results show that volumetric concentration and beta2 - a parameter related to yield stress - are the most sensitive parameters, regardless of the target variable. Additionally, different parameter sensitivities are obtained for each debris flow variable (i.e., flow velocity, flow height, deposited area, run-out, etc.)
The Planchón Peteroa Volcanic Complex (PPVC) is located on the border of Chile and Argentina, and is one of the most active volcanic systems in the Andes. Holocene activity has included magma-water interaction with an evolving series of crater lakes, mainly sourced from Peteroa volcano. This study examines data from the 2018/19 eruption, together with the volcanic history of the PPVC, to elucidate the complex interplay between magmatic activity and summit water and ice. From February 2016 to mid-2019, three seismic swarms occurred in the PPVC, preceding the explosive eruption from September 2018 to April 2019. The activity originated from a small vent nested within the easternmost crater, the most active portion of the complex (Peteroa). The explosions interacted with a crater lake, producing ash plumes up to 2 km above the crater and building a small tephra cone. To investigate the eruption mechanisms, we performed remote sensing analysis of plume dispersal, thermal anomalies and ground deformation, and characterized the volcanic products, including grain size, componentry, morphology, internal textures, composition and mineralogy. Our results suggest that the precursory seismicity beginning in 2016 was related to the intrusion of a new magma batch that reached the surface during the 2018/19 eruption. The eruption was also preceded by thermal anomalies, geomorphic changes and increased hydrothermal activity at the surface, though without any ground deformation recognized through radar interferometry (InSAR). The eruption initially produced predominantly recycled ash (phreatic activity), then evolved to increasing proportions of juvenile magma (phreatomagmatic) by April 2019. The juvenile clasts had a trachyandesite composition (~59 wt% SiO2), with vesicular and dense scoria containing plagioclase and pyroxene. The ash surfaces show external quenching cracks and step fractures consistent with phreatomagmatic fragmentation within the active crater lake. Textural characteristics also point to a slowly ascending batch of magma that was relatively viscous by the time it interacted with water in the crater lake. Notably, these juvenile particles are distinctive from the pre-2018 products. Ash erupted from 2010/11 did not contain recognizable juvenile material, and is inferred to have been a mainly phreatic eruption. Our findings suggest that the interplay between phreatic and phreatomagmatic eruptions fed by small magma batches intruding at shallow levels characterize much of the eruptive behavior of the PPVC during the last three decades. Multi-parametric assessment is a powerful tool to discriminate between phreatic and phreatomagmatic eruptions.
The purpose of this paper was to draw attention to the need for rising landslide disaster risk awareness directed to children at the local level, particularly in peri-urban mountain areas of Mexico, where high vulnerability conditions and the lowest levels of information and attention are usually found. An attempt to engage children in the co-production of basic disaster risk knowledge associated with landslide exposure founded on a community-based mapping approach was documented for the neighbourhoods of Ayotzingo and Las Moraledas, localities built as post-disaster resettlements, resulting from the disaster of October 1999 associated with rainfall-induced landslides, in the municipality of Teziutlán, Puebla, in México. The performed community-based mapping endeavour is part of the activities carried out within the framework of the ICL-IPL Project “Landslide disaster risk communication in mountain areas.” This approach indicated that analytical capabilities of community-based strategies could be used not only to contribute to the elaboration of hazard maps, but also to highlight the spatial complexity of social and environmental issues that produce and influence landslide disaster risk at the local level. Most importantly, community-based mapping workshops were useful to emphasise the importance of children’s education and participation in disaster risk reduction. In this paper, it is argued that in addition to using maps as quantitative and qualitative tools for depicting the different ingredients and interactions of historical and contemporary processes leading to the social construction of disaster risk, they are a popular and simplified view of the own space of peoples at risk that can be transformed to personal and communal awareness as an initial stage into the understanding of disaster risk and the necessity to transcend disaster response by supporting scientific evidence-based integrated disaster risk management (IDRiM). It was possible to conclude that community-based landslide mapping should be regarded as a cornerstone for landslide disaster risk awareness, favouring the co-production of knowledge by taking into account local contexts. Above and beyond all, it is considered that the sustain participation of children in DRR should be highly valued as a significant means to contribute to the challenge of curbing disaster losses and reducing disaster risk. Furthermore, it should be emphasised that the use of community-based approaches directed to children is obligated for educating the new generations due to the fact that the children of today will be the decision makers and responsible for the disaster risk governance of tomorrow.
En los últimos años, diversos estudios han señalado la existencia de una primera fase orogénica en los Andes durante el Cretácico medio a Tardío. No obstante, las evidencias directas de este evento son escasas, lo que deja abierta la pregunta respecto al real impacto de esta fase en el margen andino. En este contexto, se estudiaron las estructuras, la cronología, estratigrafía, sedimentología y proveniencia sedimentaria de la Formación Las Chilcas. Nuevas dataciones U-Pb en circones de niveles ígneos y sedimentarios de la Formación Las Chilcas permiten fijar su edad entre los 105 y 82 Ma, siendo esta dividida en cuatro miembros: Pitipeumo (105 100 Ma), Tabón (100 93 Ma), Ñilhue (92 90 Ma) y El Calvario (89 82 Ma). Conjuntamente se ha decidido separar de la base de la Formación Las Chilcas a la Formación Cerro Morado (116 106 Ma). La estructura y la estratigrafía estudiada permiten concluir que, tras un largo período de extensión durante el Cretácico Temprano, se habría iniciado, en Chile central, a aproximadamente 105 Ma, la inversión de las cuencas que acomodaron los miles de metros de lavas de la Formacion Veta Negra. Esta inversión habría permitido el desarrollo del Monoclinal El Melón, cuya carga litostática habría generado una fuerte subsidencia que desarrolló una incipiente cuenca de antepaís, depositándose en ésta el Miembro Pitipeumo. Posteriormente, durante el Cenomaniano, el proceso de inversión generó el Anticlinal Cerro Blanco, cuya erosión provocó la acumulación de cientos de metros de conglomerados sinorogénicos, correspondientes a abanicos aluviales y sistemas fluviales, asignados al Miembro Tabón. A continuación, durante el Turoniano, se instaura un sistema sedimentario de agua dulce de extensión regional (Miembro Ñilhue) mientras continúa la compresión registrada en la Falla Los Maquis. Finalmente, el establecimiento de un volcanismo importante, entre los 89 y 82 Ma (Miembro El Calvario), constata un corrimiento hacia el este del arco volcánico, a la vez que suaves pliegues y una suave discordancia con la sobreyacente Formación Lo Valle, ponen en evidencia que la compresión continuaba. Los datos de proveniencia sedimentaria de la Formación Las Chilcas permiten observar una secuencia de destechamiento de las formaciones del Cretácico Temprano. Los mismos datos sugieren que producto de la inversión se habrían exhumado otra cuenca que habría acomodado los depósitos del arco jurásico, ubicada posiblemente más al oeste. Así, la Formación Las Chilcas representa los depósitos sinorogénicos del antepaís más proximal, acumulados durante un evento de inversión que se extendió, en Chile central, desde los 105 a los cerca de 80 Ma.
Community resilience is the ability of people exposed to disasters, crises and underlying vulnerabilities, to anticipate, to prepare for, to reduce the impact of, to cope with and to recover from the effects of shocks and stresses without compromising their long-term prospects. In February 2010, the town of Maierato (Calabria, southern Italy) was hit by a large landslide, which radically changed the morphology of the territory and produced an important social and economic impact. The aim of this paper is to deal with the concepts of social vulnerability and community resilience, within the framework of the landslide risk governance and the perception of the risk. Survey was conducted by means of a structured questionnaire interviewing 200 adults. Results, analyzed by means of qualitative methods with the support of descriptive statistics, highlighted several important remarks. Globally, this case study indicates that urgent actions should be taken to reduce disaster-risk such as: improving citizens' understanding of disaster management, reinforcing risk governance to improve disaster management, investing in risk mitigation and programs fostering adaptation and resilience, improving emergency planning strategies.
The relationship between subduction in convergent margins, crustal structures and magmatism is crucial to understand processes such as the type and frequency of volcanic activity in these areas. Although it is well known that the release of fluids by the subducting slab is the main cause of the arc volcanism in areas like the Central and Southern Andes, details such as the timing and pathways of magma ascent and storage are still not well understood. A key factor that needs to be better studied in the Southern Volcanic Zone of the Andes of Chile is the role of large tectonic features in fluid transport and magma ascent processes, such as the Liquiñe-Ofqui Fault Zone, a N-S strike-slip crustal structure parallel to the main volcanic arc. In this study, we focus on Osorno volcano, a stratovolcano composed mainly by products of basaltic to basaltic-andesite composition with minor dacites and with historical Hawaiian-Strombolian eruptions. Through the measurement of magnetotellurics and the use of 3-D modeling tools and petrologic constraints, two magmatic reservoirs have been inferred, which suggest a complex magmatic system with reservoirs of different depths and compositions. The shallowest magmatic reservoir (4–8 km) has a dacitic composition, while the deepest one (7–15 km), has an andesitic composition instead. The shallow reservoir is located 2 km to the E of the volcano and the deepest one is located 10 km to the E. Considering that the Liquiñe-Ofqui Fault Zone is located 20 km to the E of the volcano, we suggest that eruptions of Osorno volcano are associated with the ascent of deep crustal basaltic magma enhanced by this master fault, re-activating the inferred reservoirs and the volcano.
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.
Tributary-junction alluvial fans situated at the intersection of confined valleys with <100 km2 tributary catchments are of special interest to evaluate the heterogeneous consequences of extreme rainfall events in arid zones. These fans record the episodic sedimentological behaviour of the hillslope response to rainstorm events within tributary catchments, together with the influence on the main fluvial systems. In this paper, we benefit from the March 2015 event (23–26 March 2015), which produced 75–46 mm of precipitation over four days in the southern portion of the Atacama Desert. This storm event triggered several debris flows in El Huasco River watershed tributaries and, therefore, tributary-junction alluvial fans received a total of ∼106 m3 of sediments across 49 activated catchments. We find that the characteristic storm signature across the catchments can be synthetised in a conceptual fan formation model based on field mapping of facies (F1 to F6) present in the fans. The characteristic signature is a record of initially high sediment-to-water flows restricted to the fan environments (mainly debris flows) followed by later, more dilute (mainly hyper-concentrated to fluvial) flows that incise the tributary-junction alluvial fan deposits and link tributary catchments with the main river. These later-stage flood event deposits, locally, are capable of ponding and compartmentalising the main river where the longitudinal connectivity of the tributary-junction catchment is effective. This situation improves tributary-junction fan slope and main-trunk-channel linkages. This approach provides a reference framework for understanding the distribution and routing of effective runoff from similar rainfall events that control the aggradation and incision of the fluvial system, which is of great value when studying past stratigraphic arrangements in these arid alleys.
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 centres in the Southern Volcanic Zone exhibiting similar temporal eruptive diversity and ultimately, has significant implications with respect to hazard assessment.
Oblique-slip tectonics in the intra-arc region of the Southern Andes accommodates heterogeneous deformation derived from plate convergence during the Pliocene and Quaternary. Long-term mechanical interaction between Andean transverse faults (i.e. NW-striking sinistral faults) and margin-parallel faults (i.e. NNE-striking faults) results in linked transtensional fault damage zones that facilitate structural conditions for the migration and emplacement of geofluids in the upper crust. We investigated the architecture of pre-eruptive units and the nature of faulting at the Tatara–San-Pedro–Pellado volcanic complex in the Southern Andes. Here, oblique-slip faulting crosscuts Miocene folded strata and granitoids. Our main results suggest that Quaternary volcanism and an associated geothermal systems developed on top of an ENE-oriented structural anisotropy defined by hundreds of faults and dikes interacting in a ca. 9 km long and 4 km wide rock volume, named the Tatara Damage Zone. Deformation in this domain is characterized by ENE- to WNW-striking transtensional oblique-slip faults flanked by (1) the seismically active NS-striking (dextral) Melado Fault to the west, (2) discrete NS- to ENE-striking dextral splay faults to the east and (3) the sinistral NW-striking Los Cóndores Fault to the north-east, which is reported for the first time in this work. The latter fault represents an excellent example of a long-lived Andean Transverse Fault. Furthermore, we suggest that the Los Cóndores Fault accommodates a margin-oblique slip component of bulk transpressional deformation. We demonstrate that Pliocene–Quaternary intra-arc oblique faulting developed after pre-Late Miocene compressional tectonics, and that this oblique faulting constrains the geometry of permeable pathways for the flow, emplacement, and eruption of quaternary geofluids. Furthermore, we evaluated the stress field for a discrete volcanic complex and provided key elements to better understand the role of Andean Transverse Faults in the spatial organization of Quaternary arc volcanism and geothermal systems in the Southern Andes.
Debris flows occur in mountainous areas characterized by steep slope and occasional severe rainstorms. The massive urbanization in these areas raised the importance of studying and mitigating these phenomena. Concerning the strategy of protection, it is fundamental to evaluate both the effect of the magnitude (that concerns the definition of the hazard), in terms of mobilized volume and travel distance, and the best technical protection structures (that concerns the mitigation measures) to reduce the existing risk to an acceptable residual one. In particular, the mitigation measure design requires the evaluation of the effects of debris flow impact forces against them. In other words, once it is established that mitigation structures are required, the impacting pressure shall be evaluated and it should be verified that it does not exceed barrier resistance. In this paper, the author wants to focus on the definition and the evaluation of the impacting load of debris flows on protection structures: a critical review of main existing models and equations treated in scientific literature is here presented. Although most of these equations are based on solid physical basis, they are always affected by an empirical nature due to the presence of coefficients for fitting the numerical results with laboratory and, less frequently, field data. The predicting capability of these equations, namely the capability of fitting experimental/field data, is analysed and evaluated using ten different datasets available in scientific literature. The purpose of this paper is to provide a comprehensive analysis of the existing debris flow impact models, highlighting their strong points and limits. Moreover, this paper could have a practical aspect by helping engineers in the choice of the best technical solution and the safe design of debris flow protection structures. Existing design guidelines for debris flow protection barrier have been analysed. Finally, starting from the analysis of the hydro-static model response to fit field data and introducing some practical assumptions, an empirical formula is proposed for taking into account the dynamic effects of the phenomenon.
The first comprehensive global database of giant landslides on volcanic islands is outlined in this report. This database comprises a total of one hundred and eighty-two entries: the Atlantic Ocean hosts seventy-five giant landslides; the Pacific Ocean hosts sixty-seven giant landslides; and the Indian Ocean hosts forty giant landslides. To determine the spatial characteristics of each giant landslide, it has been necessary to georeference published maps using ArcGIS software coupled with global DTMs. Using the georeferenced outputs, it has been possible to measure the basic morphometric characteristics of each landslide such as its length, width, perimeter, area, and fall height. Landslide volumes have been calculated with a higher degree of certainty in thirty-five cases and with a lower degree of certainty in sixty-three cases while complete outlines of the landslide area have been defined in ninety-six cases. On the basis of these data, it has been possible to interrogate relationships between potentially significant variables. The age distribution of giant landslides on volcanic islands demonstrates that more than half of the records in the database occurred during the last 0.5 Ma. This global database of giant landslides on volcanic islands is hosted on the website of the Institute of Rock Structure & Mechanics: https://www.irsm.cas.cz/ext/giantlandslides. From there, the records can be downloaded as a spreadsheet or as a kml file for interrogation in a number of geospatial software programs including ArcGIS and Google Earth. This work is part of the activities of the International Consortium on landslides, namely, its International Programme on Landslides (Project No. 212).
Volcanogenic tsunamis are one of the deadliest volcanic phenomena. Understanding their triggering processes, and mitigating their effect, remains a major challenge. On 22 December 2018, flank failure of the Anak Krakatau volcano in Indonesia generated a tsunami that killed more than 400 people. This event was captured in unprecedented detail by high-resolution satellite imagery and eyewitness accounts. Here we combine historic observations with these recent data to—for the first time—interpret the internal architecture of Anak Krakatau, and reconstruct the failure, tsunamigenesis, and regrowth processes observed. We calculate the volume of material initially lost from the volcano flank failure and find that it was relatively small (~0.1 km3) compared to the overall changes observed during the entire eruption, but it was nonetheless able to generate rapid tsunami waves with devastating impacts. The flank failure also changed the eruption style and the upper volcanic plumbing system, with the subsequent explosive eruptions destroying the summit and then partially rebuilding the lost flank. The nature of the flank failure was controlled by the internal structure of the island, and—although regrowth rate will be a primary control on flank failure intervals—the reconfiguring of the volcano’s internal vent network is likely to have re-stabilized it in the medium term. The findings demonstrate that hazard assessments at ocean islands must consider that even small flank failures, during unexceptional eruptions, can have catastrophic consequences.
Sector collapses affect volcanic edifices across all tectonic settings and involve a rapid redistribution of mass, comparable in scale to the largest magmatic eruptions. The eruptive behaviour of a volcano following sector collapse provides a test of theoretical relationships between surface loading and magma storage, which imply that collapse-driven unloading may lead to changes in eruption rate and erupted magma compositions. Large sector collapses are infrequent events globally, with all historical examples being relatively small in comparison to many of the events documented in the geological record. As a result, exploration of the impacts of sector collapse on eruptive behaviour requires detailed investigation of prehistoric collapses, but this is often hindered by poorly-resolved stratigraphic relationships and dating uncertainties. Nevertheless, observations from a number of volcanoes indicate sharp changes in activity following sector collapse. Here, a global synthesis of studies from individual volcanoes, in both arc and intraplate settings, is used to demonstrate a number of common processes in post-collapse volcanism. Multiple examples from large (>5 km³) sector collapses in arc settings show that collapse may be followed by compositionally anomalous, large-volume and often effusive eruptions, interpreted to originate via disruption of a previously stable, upper-crustal reservoir. These anomalous eruptions highlight that magma compositions erupted during periods of typical (i.e. unperturbed by sector collapse) volcanism may not be representative of the range of compositions stored within a vertically extensive crustal reservoir. If eruptible magma is not present, upper-crustal reservoirs may rapidly solidify following collapse, without further eruption, allowing more mafic compositions to ascend to the surface with only limited upper-crustal modification, resulting in edifice regrowth at temporarily elevated eruption rates. Subsequent re-establishment of an upper-crustal reservoir further supports a relationship between surface loading and crustal storage, but long-term chemical and mineralogical differences between pre- and post-collapse evolved magmas imply that a newly-developed reservoir can overprint the influence of a preceding reservoir, forming a spatially and compositionally distinct plumbing system. These broad patterns are replicated in intraplate settings, despite differences in scale and melting processes; current evidence suggests that post-collapse evolution of intraplate volcanoes can be explained by unloading-induced destabilisation of the magma plumbing system, rather than increased melt production. What emerges from an apparently diverse set of observations is a systematic behaviour that strongly supports a coupling between edifice growth and magma ascent, storage and pressurisation. Eruption rates, erupted compositions, and the style of volcanism at any particular system may thus be modulated from the surface, and long-term shifts in surface behaviour may occur without any changes in the deep parts of magmatic systems. Observations of sharp post-collapse changes in erupted compositions, including the ascent of primitive mafic magmas, also require a crystal-dominated mid- to upper-crustal reservoir, consistent with recent models of crustal magmatic systems.
The current understanding of tsunamis generated by volcanic-island landslides is reliant on numerical models benchmarked against reconstructions of past events. As the largest historical event with timed tsunami observations, the 1888 sector collapse of Ritter Island, Papua New Guinea provides an outstanding opportunity to better understand the linked process of landslide emplacement and tsunami generation. Here, we use a combination of geophysical imaging, bathymetric mapping, seafloor observations and sampling to demonstrate that the Ritter landslide deposits are spatially and stratigraphically heterogeneous, reflecting a complex evolution of mass-flow processes. The primary landslide mass was dominated by well-bedded scoriaceous deposits, which rapidly disintegrated to form an erosive volcaniclastic flow that incised the substrate over much of its pathway. The major proportion of this initial flow is inferred to have been deposited up to 80 km from Ritter. The initial flow was followed by secondary failure of seafloor sediment, over 40 km from Ritter. The most distal part of the 1888 deposit has parallel internal boundaries, suggesting that multiple discrete units were deposited by a series of mass-flow processes initiated by the primary collapse. The last of these flows was derived from a submarine eruption triggered by the collapse. This syn-collapse eruption deposit is compositionally distinct from pre- and post-collapse eruptive products, suggesting that the collapse immediately destabilised the underlying magma reservoir. Subsequent eruptions have been fed by a modified plumbing system, constructing a submarine volcanic cone within the collapse scar through at least six post-collapse eruptions. Our results show that the initial tsunami-generating landslide at Ritter generated a stratigraphically complex set of deposits with a total volume that is several times larger than the initial failure. Given the potential for such complexity, there is no simple relationship between the volume of the tsunamigenic phase of a volcanic-island landslide and the final deposit volume, and deposit area or run-out cannot be used to infer primary landslide magnitude. The tsunamigenic potential of prehistoric sector-collapse deposits cannot, therefore, be assessed simply from surface mapping, but requires internal geophysical imaging and direct sampling to reconstruct the event.
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Volcanic island flank collapses have the potential to trigger devastating tsunamis threatening coastal communities and infrastructure. The 1888 sector collapse of Ritter Island, Papua New Guinea (in the following called Ritter) is the most voluminous volcanic island flank collapse in historic times. The associated tsunami had run-up heights of more than 20 m on the neighboring islands and reached settlements 600km away from its source. This event provides an opportunity to advance our understanding of volcanic landslide-tsunami hazards. Here, we present a detailed reconstruction of the 1888 Ritter sector collapse based on high-resolution 2D and 3D seismic and bathymetric data covering the failed volcanic edifice and the associated mass-movement deposits. The 3D seismic data reveal that the catastrophic collapse of Ritter occurred in two phases: (1) Ritter was first affected by deep-seated, gradual spreading over a long time period, which is manifest in pronounced compressional deformation within the volcanic edifice and the adjacent seafloor sediments. A scoria cone at the foot of Ritter acted as a buttress, influencing the displacement and deformation of the western flank of the volcano and causing shearing within the volcanic edifice. (2) During the final, catastrophic phase of the collapse, about 2.4km3 of Ritter disintegrated almost entirely and traveled as a highly energetic mass flow, which incised the underlying sediment. The irregular topography west of Ritter is a product of both compressional deformation and erosion. A crater-like depression underlying the recent volcanic cone and eyewitness accounts suggest that an explosion may have accompanied the catastrophic collapse. Our findings demonstrate that volcanic sector collapses may transform from slow gravitational deformation to catastrophic collapse. Understanding the processes involved in such a transformation is crucial for assessing the hazard potential of other volcanoes with slowly deforming flanks such as Mt. Etna or Kilauea.