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Hidetsugu Yoshida - One of the best experts on this subject based on the ideXlab platform.
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volcanic Debris Avalanche transport and emplacement mechanisms
2021Co-Authors: E M R Paguican, Matteo Roverato, Hidetsugu YoshidaAbstract:Field observations of volcanic Debris Avalanche (VDA) morphology, sedimentology, and structural features have inspired several hypotheses on their dynamic behaviour. These include plug flow, translational slide, and sliding along multiple shear zones, none of which involve large-scale turbulence during transport. The plug flow model shows normal gradation in the plug, and reverse grading in the laminar boundary layers. During translational sliding, spreading of the mass is accommodated by listric normal faults that flatten into a main sliding plane at the base of or within the Avalanche body. Multiple shear zones include progressive fragmentation within the avalanching mass, resulting in pockets of shear and slip. We present case studies for each model and hypotheses for the formation of flowbands on the deposit surface. Processes involved during emplacement include disintegration, dynamic fragmentation, and matrix injection. Near the base, bulldozing and incorporation of substrata change the composition and behaviour of the VDA. In extreme cases, VDAs transform into lahars if sufficient water is available for entrainment. Post-emplacement, lahars can also happen, e.g., through Debris dewatering, loading of saturated substrata or in the case of landslide dam failure. VDA also create secondary slides when deflected by topographic barriers or when the margins are oversteepened.
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Characteristics of Debris Avalanche deposits inferred from source volume estimate and hummock morphology around Mt. Erciyes, central Turkey
Natural Hazards and Earth System Sciences, 2018Co-Authors: Yuichi S. Hayakawa, Hidetsugu Yoshida, Hiroyuki Obanawa, Ryutaro Naruhashi, Koji Okumura, Masumi Zaiki, Ryoichi KontaniAbstract:Abstract. Debris Avalanches caused by volcano sector collapse often form characteristic depositional landforms such as hummocks. Sedimentological and geomorphological analyses of Debris Avalanche deposits (DADs) are crucial to clarify the size, mechanisms, and emplacement of Debris Avalanches. We describe the morphology of hummocks on the northeastern flank of Mt. Erciyes in Kayseri, central Turkey, likely formed in the late Pleistocene. Using a remotely piloted aircraft system (RPAS) and the structure-from-motion and multi-view stereo (SfM–MVS) photogrammetry, we obtained high-definition digital elevation model (DEM) and orthorectified images of the hummocks to investigate their geometric features. We estimated the source volume of the DAD by reconstructing the topography of the volcano edifice using a satellite-based DEM. We examined the topographic cross sections based on the slopes around the scar regarded as remnant topography. Spatial distribution of hummocks is anomalously concentrated at a certain distance from the source, unlike those that follow the distance–size relationship. The high-definition land surface data by RPAS and SfM revealed that many of the hummocks are aligned toward the flow direction of the Debris Avalanche, suggesting that the extensional regime of the Debris Avalanche was dominant. However, some displaced hummocks were also found, indicating that the compressional regime of the flow contributed to the formation of hummocks. These indicate that the flow and emplacement of the Avalanche were constrained by the topography. The existing caldera wall forced the initial eastward flow to move northward, and the north-side caldera wall forced the flow into the narrow and steepened outlet valley where the sliding Debris underwent a compressional regime, and out into the unconfined terrain where the Debris was most likely emplaced on an extensional regime. Also, the estimated volume of 12–15 × 10 8 m 3 gives a mean thickness of 60–75 m, which is much deeper than the reported cases of other DADs. This suggests that the Debris Avalanche must have flowed further downstream and beyond the current DAD extent. Assessments of the DAD incorporating the topographic constraints can provide further insights into the risk and mitigation of potential disasters in the study area.
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Morphological analysis of hummocks in Debris Avalanche deposits around Mt Erciyes, central Turkey
2017Co-Authors: Yuichi S. Hayakawa, Hidetsugu Yoshida, Hiroyuki Obanawa, Ryutaro Naruhashi, Koji Okumura, Masumi Zaiki, Ryoichi KontaniAbstract:Debris Avalanche caused by the sector collapse of a volcanic mountain often forms characteristic depositional landforms including hummocks. Not only sedimentological but also geomorphological analyses of Debris Avalanche deposits (DAD) are crucial to clarify the size, mechanisms, and processes of the Debris Avalanche. We investigate the morphology of hummocks newly identified in the DAD at the north-eastern flank of Mt. Erciyes in Kayseri, central Turkey, likely formed in the late Pleistocene. Using a remotely piloted aircraft system (RPAS) and the structure-from-motion multi-view stereo photogrammetry (SfM), we obtained high-definition digital elevation model (DEM) and orthorectified image of the DAD surface with hummocks. Detailed geometric features of the hummocks are investigated using the RPAS-derived high-definition DEM. The source volume of the DAD was also estimated by reconstructing the original shape of the mountain body using a lower-resolution satellite-based DEM. For this, topographic cross sections are examined based on the slopes around the scar that are regarded as the remnant topography preserved since the sector collapse. The spatial distribution of hummocks shows an unusual pattern regarding the distance-size relationships, i.e., anomalously concentrated in a certain distance from the source. The hummocks are found to be aligned toward the flow direction of the Debris Avalanche, suggesting the extensional regime of the Debris Avalanche. These facts indicate that this Debris Avalanche did not follow the typical flow type of Debris Avalanches observed in the other cases. Instead, the topographic constraints by former caldera wall and fault-induced lineaments could have strongly affected the flow course and pattern in this particular case: The pre-existing caldera wall topography could have acted as the topographic barriers for the Debris Avalanche to force the initial flow to turn northward, and the flow regime to be once compressional followed by extensional at the narrow and steepened outlet valley. Also, the estimated volume of the DAD 12–15 × 10 8 m 3 gives its mean thickness of 60–75 m, which is much deeper than the reported cases of other DADs. This suggests that the Debris Avalanche could have flown down to the far downstream areas from the presently-observed limit of the DAD extent. Assessments of the DAD including the results of this study can provide further insights into the risk and mitigation of potential disasters in the study area.
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Magnitude-Frequency Distribution of Hummocks on Rockslide-Debris Avalanche Deposits and Its Geomorphological Significance
Geosciences, 2016Co-Authors: Hidetsugu YoshidaAbstract:A magnitude-frequency analysis of rockslide-Debris Avalanche deposits was performed. Hummocks are conical mounds formed in Debris Avalanche deposits from the catastrophic sector collapse of a mountain (often volcanic) that represent relatively cohesive fragments of the mountain edifice. Examination of 17 Debris Avalanche deposits in Japan and the Philippines showed that, in general, the larger the magnitude of the hummocks, the smaller their frequency. Hummocks followed an exponential distribution: log10N(x) = a – bx, where N(x) is the cumulative number of hummocks with magnitude ≥ x and a and b are constants; x is equal to log10A, where A is the area of a hummock. The constants a and b were positively correlated. The value of b, which differs among Avalanches and in this analysis ranged between 1 and 3, may be controlled by the mobility of the Debris Avalanche. Avalanches with higher mobility (relatively longer runout) have higher b and potentially produce more numerous fragments forming hummocks (i.e., higher a). From the above correlation, the magnitude-frequency relationship can be used to roughly estimate the original height of the collapsed volcanic body, if the runout distance of the rockslide–Debris Avalanche can be estimated with sufficient accuracy.
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Decrease of size of hummocks with downstream distance in the rockslide-Debris Avalanche deposit at Iriga volcano, Philippines: similarities with Japanese Avalanches
Landslides, 2013Co-Authors: Hidetsugu YoshidaAbstract:A morphometric investigation of the longitudinal distribution of hummocks at the southeastern foot of Iriga volcano in the Philippines showed that hummock size decreases away from the volcano. Aerial photographs and GIS analysis revealed that the size–distance relationship can be expressed as the exponential function A = α exp (−β D), where A is the area of a hummock and D is its distance from the source. This relationship is the same as that observed previously for freely spreading Debris Avalanches in Japan, including two Avalanches at Bandai volcano. This size–distance relationship provides information about the physical characteristics of the event: the α value shows a strong correlation with the volume of the collapsed mass of the volcanic edifice, and the β value shows a strong correlation with the coefficient of friction of the Debris Avalanche. Thus, morphometric analysis of hummocks created by a volcanic Avalanche illuminates both the physical properties of the volcanic body and the mobility of the Avalanche. For the Iriga Debris Avalanche, the observed longitudinal hummock distribution is clearly a function of the volume of the collapsed mass and the coefficient of friction of the Avalanche. The relationships so defined appear to be a geometric effect related to the areal extent of freely spreading hummocky Avalanche deposits, especially their longitudinal dimensions.
Marcos Báez - One of the best experts on this subject based on the ideXlab platform.
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geological history and within island diversity a Debris Avalanche and the tenerife lizard gallotia galloti
Molecular Ecology, 2006Co-Authors: Richard P. Brown, Paul A. Hoskisson, John-henry Welton, Marcos BáezAbstract:Several processes have been described that could explain geographical variation and speciation within small islands, including fragmentation of populations through volcanic eruptions. Massive landslides, or Debris Avalanches, could cause similar effects. Here we analyse the potential impact of the 0.8 million-year-ago (Ma) Guimar valley Debris Avalanche on the phylogeography of the lizard Gallotia galloti on the Canary Island of Tenerife. Distributions of mitochondrial DNA lineages (based on cytochrome b sequences) were analysed on a 60-km southeastern coast transect centred on this area. Three main clades were detected, which can be divided into northern (one clade) and southern (two clades) groups that introgress across the valley. Maximum-likelihood estimates of migration rates (scaled for mutation rate) revealed highly asymmetric patterns, indicating that long-term gene flow into this region from both the northern and the southern populations greatly exceeded that in the opposite directions, consistent with recolonization of the area. The ancestral Tenerife node on the G. galloti tree is estimated at 0.80 Ma, matching closely with the geological estimate for the Debris Avalanche. Morphological variation (body dimensions and scalation) was also analysed and indicated a stepped cline in female scalation across the valley, although the patterns for male scalation and male and female body dimensions were not as clear. Together these findings provide support for the hypothesis that the Debris Avalanche has shaped the phylogeography of G. galloti and may even have been a primary cause of the within-island cladogenesis through population fragmentation and isolation. Current estimates of timing of island unification mean that the original hypothesis that within-island diversity is explained by the secondary contact of populations from the two ancient precursor islands of Teno and Anaga is less plausible for this and some other Tenerife species. Large-scale landslides have occurred on many volcanic islands, and so may have been instrumental in shaping within-island diversities.
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Geological history and within‐island diversity: a Debris Avalanche and the Tenerife lizard Gallotia galloti
Molecular ecology, 2006Co-Authors: Richard P. Brown, Paul A. Hoskisson, John-henry Welton, Marcos BáezAbstract:Several processes have been described that could explain geographical variation and speciation within small islands, including fragmentation of populations through volcanic eruptions. Massive landslides, or Debris Avalanches, could cause similar effects. Here we analyse the potential impact of the 0.8 million-year-ago (Ma) Guimar valley Debris Avalanche on the phylogeography of the lizard Gallotia galloti on the Canary Island of Tenerife. Distributions of mitochondrial DNA lineages (based on cytochrome b sequences) were analysed on a 60-km southeastern coast transect centred on this area. Three main clades were detected, which can be divided into northern (one clade) and southern (two clades) groups that introgress across the valley. Maximum-likelihood estimates of migration rates (scaled for mutation rate) revealed highly asymmetric patterns, indicating that long-term gene flow into this region from both the northern and the southern populations greatly exceeded that in the opposite directions, consistent with recolonization of the area. The ancestral Tenerife node on the G. galloti tree is estimated at 0.80 Ma, matching closely with the geological estimate for the Debris Avalanche. Morphological variation (body dimensions and scalation) was also analysed and indicated a stepped cline in female scalation across the valley, although the patterns for male scalation and male and female body dimensions were not as clear. Together these findings provide support for the hypothesis that the Debris Avalanche has shaped the phylogeography of G. galloti and may even have been a primary cause of the within-island cladogenesis through population fragmentation and isolation. Current estimates of timing of island unification mean that the original hypothesis that within-island diversity is explained by the secondary contact of populations from the two ancient precursor islands of Teno and Anaga is less plausible for this and some other Tenerife species. Large-scale landslides have occurred on many volcanic islands, and so may have been instrumental in shaping within-island diversities.
Lucia Capra - One of the best experts on this subject based on the ideXlab platform.
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Late Pleistocene-Holocene Debris Avalanche Deposits from Volcán de Colima, Mexico
Volcán de Colima, 2019Co-Authors: A. Cortés, Jean-christophe Komorowski, José Luis Macías, Lucia Capra, Paul W. LayerAbstract:Volcan de Colima has experienced numerous partial edifice collapses with associated Debris Avalanche deposits, widely distributed toward the SW, S and SE sectors. According to new 40Ar/39Ar dates, activity began more than 97,000 years ago on the southern flank of Nevado de Colima with the formation of the so-called Paleofuego edifice. Several collapses occurred prior to a catastrophic edifice collapse event 7000 years ago, creating a horseshoe-shaped Avalanche crater, 5 km wide, opened towards the south. After this last lateral collapse of Paleofuego, the currently active cone began to grow in the central part of the crater, which, during the Late Holocene, has experienced two lateral collapse events that generated Debris Avalanches. Based on new fieldwork and stratigraphic correlation of deposits supported by 14C dates, we present a description and approximate distribution of eight Debris Avalanche deposits generated by Volcan de Colima during the last 30,000 years. These Debris Avalanche deposits are exposed at 40 km to the S and 25 km in the SW and SE sectors of the volcano, and cover an area of 1200 km2 with an approximated volume of 86 km3. Field evidence indicates that at least some sector collapses were accompanied by magmatic activity. The regional tectonic setting that consists of the active N-S regional extension of the Colima graben, as well as E-W, and NE-SW structures, such as the Tamazula Fault, also played an important role in volcano instability. The contribution of a volcanic spreading component was also recently recognized. The emplacement of the most voluminous Debris Avalanches have obstructed the Armeria and Tuxpan-Naranjo rivers producing temporary lakes, where thick lacustrine sediments were accumulated. The recurrence times of these sector collapses vary between 3000 and 6500 years during the Late Pleistocene and 1100–3400 years during the Holocene, with the youngest one having occurred ~2.5 ka BP. A future sector collapse of Volcan de Colima on the scale of past events could be catastrophic for up to about 350,000 inhabitants (including the city of Colima) that currently are located on top of ancient Debris Avalanche deposits.
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Textural features as indicators of Debris Avalanche transport and emplacement, Taranaki volcano
Geological Society of America Bulletin, 2014Co-Authors: Matteo Roverato, Shane J. Cronin, Jonathan Procter, Lucia CapraAbstract:The Pungarehu Debris Avalanche deposit was emplaced by the largest known collapse of the proto–Taranaki volcano, ca. 25,000 calibrated (cal.) years ago. This Debris Avalanche deposit displays a highly contrasting sedimentary character between its proximal and distal reaches. Examination of the deposit granulometry, sedimentary structures, and microscopic particle attributes provides new insights into Debris Avalanche transport and internal evolution processes. Initial collapse of the proto–Taranaki volcano during this event occurred near the Last Glacial Maximum, with snow and ice cover and substantial groundwater present. The collapsing, sliding large blocks of edifice material, “megaclasts,” were highly fractured by the landslide generation and the depressurization event, forming pervasive jigsaw textures. As the megaclasts moved, shear was focused in softer domains between the hardest, lava-dominated lithologies. These crush and shear zones developed a complex pattern of relative motion between horizontal and vertical parts of the landslide, rather than a simple basal shear zone that supported an upper pluglike mass. The sheared zones, concentrated in soft, pyroclastic lithologies, were areas of intense synflow fragmentation, producing a proto-interclast matrix between large blocks of coherent (albeit jigsaw fractured) lavas. Down flow, the interclast matrix component increased to become pervasive by ~23–25 km from the source, enveloping and preserving large megaclasts out to at least 30 km. The most distal exposures, limited by coastal erosion to ~25–27 km, show that the matrix was not completely water saturated, with only superficial penetration of the sand-dominated material into the margins of fractured lava domains, which still contained central void space. Evidence of multiple generations of particle fracturing is seen under scanning electron microscopy of sand-grade clasts, with initial decompression fractures crosscut by later cracks, pits, and scratches produced by collisional and frictional processes during transport. The findings from this study help to explain the formation of the highly irregular topography of Debris Avalanche deposits, with chaotically distributed (and probably temporary) zones of shear developing where softer lithologies occur in a collapsing mass, thus leading to differential velocity profiles of portions of the flowing mass in vertical and horizontal planes.
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Stratigraphic reconstruction of two Debris Avalanche deposits at Colima Volcano Mexico Insights into pre-failure conditions and climate influence
Journal of Volcanology and Geothermal Research, 2011Co-Authors: Matteo Roverato, Lucia Capra, Roberto Sulpizio, Gianluca NoriniAbstract:Abstract Throughout its history, Colima Volcano has experienced numerous partial edifice collapses with associated emplacement of Debris Avalanche deposits of contrasting volume, morphology and texture. A detailed stratigraphic study in the south-eastern sector of the volcano allowed the recognition of two Debris Avalanche deposits, named San Marcos (> 28,000 cal yr BP, V = ~ 1.3 km 3 ) and Tonila (15,000–16,000 cal yr BP, V = ~ 1 km 3 ). This work sheds light on the pre-failure conditions of the volcano based primarily on a detailed textural study of Debris Avalanche deposits and their associated pyroclastic and volcaniclastic successions. Furthermore, we show how the climate at the time of the Tonila collapse influenced the failure mechanisms. The > 28,000 cal yr BP San Marcos collapse was promoted by edifice steep flanks and ongoing tectonic and volcanotectonic deformation, and was followed by a magmatic eruption that emplaced pyroclastic flow deposits. In contrast, the Tonila failure occurred just after the Last Glacial Maximum (22,000–18,000 cal BP) and, in addition to the typical Debris Avalanche textural characteristics (angular to sub-angular clasts, coarse matrix, jigsaw fit) it shows a hybrid facies characterized by Debris Avalanche blocks embedded in a finer, homogenous and partially cemented matrix, a texture more characteristic of Debris flow deposits. The Tonila Debris Avalanche is directly overlain by a 7-m thick hydromagmatic pyroclastic succession. Massive Debris flow deposits, often more than 10 m thick and containing large amounts of tree trunk logs, represent the top unit in the succession. Fluvial deposits also occur throughout all successions; these represent periods of highly localized stream reworking. All these lines of evidence point to the presence of water in the edifice prior to the Tonila failure, suggesting it may have been a weakening factor. The Tonila failure appears to represent an anomalous event related to the particular climatic conditions at the time of the collapse. The presence of extensive water at the onset of deglaciation modified the mobility of the Debris Avalanche, and led to the formation of a thick sequence of Debris flows. The possibility that such a combination of events can occur, and that their probability is likely to increase during the rainy season, should be taken into consideration when evaluating hazards associated with future collapses at Colima volcano.
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textural analysis of particles from el zaguan Debris Avalanche deposit nevado de toluca volcano mexico evidence of flow behavior during emplacement
Journal of Volcanology and Geothermal Research, 2011Co-Authors: Lizeth Caballero, Lucia CapraAbstract:Abstract El Zaguan deposit originated at 28,000 yrs. B.P. from the flank collapse of Nevado de Toluca, a dacitic stratovolcano of the Transmexican Volcanic Belt. Scanning Electron Microprobe analyses (SEM) were performed on some particles from this deposit to observe microtextures produced during transport and emplacement of the Debris Avalanche flow. Particles from 2ϕ (250 μm), 0ϕ (1 mm) and − 2ϕ (4 mm) granulometric classes were randomly selected at different outcrops, and their surface textures were described. The observed textures are divided in two groups, Basal and Upper textures, each one indicating different clast interactions. Basal textures are observed predominantly in the lower part of the deposit and consist of parallel ridges, parallel grooves, scratches and lips. Upper textures are mainly present in the upper part of the deposit and consisted of fractures, percussion marks, and broken or grinded crystals. These characteristics, coupled with field observations such as the presence of clastic dikes and deformed lacustrine mega-blocks, indicate that the basal part of the Debris Avalanche was moving in a partially liquefied state. By contrast, the particles in the upper part were able to move freely, interacting by collision. These microscopic textures are in agreement with previously described emplacement behaviors in Debris Avalanches of volcanic origin, suggesting a stratified flow dominated by different transport and depositional mechanisms depending upon flow depth and possible fluid content at their base.
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sector collapse of the sw flank of volcan de colima mexico the 3600 yr bp la lumbre los ganchos Debris Avalanche and associated Debris flows
Journal of Volcanology and Geothermal Research, 2010Co-Authors: A. Cortés, José Luis Macías, Lucia Capra, Victor Hugo GardunomonroyAbstract:Abstract Some 3600 years ago the SW flank of Volcan de Colima collapsed, generating a Debris Avalanche that travelled 25 km to the Armeria River and stopped against the Cerro Grande limestone escarpment. The Debris Avalanche deposit covers an area of 48 km2, has an average thickness of 35 m, and a volume of 1.7 km3, with an H/L ratio of 0.13. Along the La Lumbre ravine, the deposit forms a series of flat terraces up to 65 m thick. A pyroclastic flow deposit overlies the Debris Avalanche deposit, suggesting that the Colima collapse was accompanied by a magmatic component. The Debris Avalanche deposit dammed the Armeria River, forming a temporary lake that accumulated a water volume of ∼ 0.19 km3. The subsequent breaking of the dam formed a Debris flow that travelled at least 20 km along the Armeria River, emplacing 15–70 m thick deposits. The Debris flow deposits cover a surface of 6.4 km2 and have a volume of ∼ 0.2 km3. The Avalanche deposit contains fragments of carbonized wood that where dated at 3600 ± 120 yr. BP by Komorowski et al. (1997). This deposit underlies a younger Debris Avalanche (2505 ± 45 yr BP), and a Debris flow deposit with pottery shards and charcoal dated at 1940 ± 90 yr BP. These pottery shards likely related to the Capacha people (820–300 yr BC) indicating that the region has been inhabited during the last 3000 years. A future collapse of Volcan de Colima in the same direction may affect several towns for a total population of circa 40,000.
Hiroo Ohmori - One of the best experts on this subject based on the ideXlab platform.
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Size–distance relationships for hummocks on volcanic rockslide-Debris Avalanche deposits in Japan
Geomorphology, 2012Co-Authors: Hidetsugu Yoshida, Toshihiko Sugai, Hiroo OhmoriAbstract:Abstract Catastrophic collapse of volcanic edifices and the accompanying rockslide-Debris Avalanches drastically change landforms and cause disasters around volcanoes. Rapid modification of the landforms created by these events makes it difficult to estimate the magnitudes of prehistoric events and evaluate damage. However, the widespread preservation of hummocks along the course of rockslide-Debris Avalanches is useful for understanding the physical characteristics of these landslides. We analyzed data on hummocks from seven prehistoric events in northern Japan to derive the relationship between hummock size and distance from landslide source, and interpreted the geomorphic significance of the intercept and slope coefficients of the observed functional relationships. Hummock size decreases as an exponential function of distance for volcanic rockslide-Debris Avalanches, although each event has its own distinct distribution pattern. The intercept coefficient, α, which corresponds to the initial average size of hummocks (blocks) at the origin of the landslide, shows a strong correlation with the volume of the collapsed mass, indicating that the initial size of blocks at the source may be determined by the volume of the collapsed mass. The slope coefficient, β, which describes the rate of decrease in size of hummocks with distance, shows a strong correlation with the coefficient of friction of the rockslide-Debris Avalanche, indicating that the attrition or size decrease rate of hummocks is controlled by the mobility of the Avalanche. These relationships enable us to estimate the volume of the collapsed mass and the travel distance of an Avalanche. Because it is sometimes difficult to obtain the evidence directly indicating the volume of collapses and the damage they caused, the findings are significant also for hazard assessment that the size–distance relationships of hummocks can be obtained from fragmentary remnants of a rockslide-Debris Avalanche to help reveal the characteristics of the events.
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size distance relationships for hummocks on volcanic rockslide Debris Avalanche deposits in japan
Geomorphology, 2012Co-Authors: Hidetsugu Yoshida, Toshihiko Sugai, Hiroo OhmoriAbstract:Abstract Catastrophic collapse of volcanic edifices and the accompanying rockslide-Debris Avalanches drastically change landforms and cause disasters around volcanoes. Rapid modification of the landforms created by these events makes it difficult to estimate the magnitudes of prehistoric events and evaluate damage. However, the widespread preservation of hummocks along the course of rockslide-Debris Avalanches is useful for understanding the physical characteristics of these landslides. We analyzed data on hummocks from seven prehistoric events in northern Japan to derive the relationship between hummock size and distance from landslide source, and interpreted the geomorphic significance of the intercept and slope coefficients of the observed functional relationships. Hummock size decreases as an exponential function of distance for volcanic rockslide-Debris Avalanches, although each event has its own distinct distribution pattern. The intercept coefficient, α, which corresponds to the initial average size of hummocks (blocks) at the origin of the landslide, shows a strong correlation with the volume of the collapsed mass, indicating that the initial size of blocks at the source may be determined by the volume of the collapsed mass. The slope coefficient, β, which describes the rate of decrease in size of hummocks with distance, shows a strong correlation with the coefficient of friction of the rockslide-Debris Avalanche, indicating that the attrition or size decrease rate of hummocks is controlled by the mobility of the Avalanche. These relationships enable us to estimate the volume of the collapsed mass and the travel distance of an Avalanche. Because it is sometimes difficult to obtain the evidence directly indicating the volume of collapses and the damage they caused, the findings are significant also for hazard assessment that the size–distance relationships of hummocks can be obtained from fragmentary remnants of a rockslide-Debris Avalanche to help reveal the characteristics of the events.
Claus Siebe - One of the best experts on this subject based on the ideXlab platform.
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substrate deformation associated with the jocotitlan edifice collapse and Debris Avalanche deposit central mexico
Journal of Volcanology and Geothermal Research, 2010Co-Authors: Anja Dufresne, Sergio Salinas, Claus SiebeAbstract:Abstract An impressive Debris Avalanche deposit is preserved at Jocotitlan volcano in Central Mexico. The northern flank of this edifice collapsed ∼ 9690 years B.P. resulting in a 80 km 2 -covering clast-supported deposit that lacks substantial matrix, fine, weak or hydrothermally altered materials. The deposit can be subdivided into three morphologically distinct areas which are each accompanied by specific, and often unique, deformation features in the underlying and adjacent volcaniclastic and lacustrine sediments. From these features, a complex history of pre- and syn-Avalanche events was reconstructed beginning with edifice-spreading on the weak substrate material prior to and in preparation of part of the flank collapse event. The north-eastern flank in particular was strongly coupled with the deforming substrate material as is still evident in its extensional profile and the unique mode of failure during the catastrophic event resulting in the deposition of what resembles non-volcanic blockslide deposits rather than the typical hummocky volcanic Debris Avalanche morphology. This latter type of failure occurred at the north-western flank of Jocotitlan volcano where few signs of substrate interactions are preserved in a deposit dominated by large conical hummocks. In addition to substrate response, interaction with pre-Avalanche topography in the eastern deposit area facilitated the emplacement of a lobe roughly perpendicular to the flank failure direction, at apparent high emplacement velocity, and with longitudinal ridges as its most striking surface expression.
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morphology and emplacement of an unusual Debris Avalanche deposit at jocotitlan volcano central mexico
Bulletin of Volcanology, 1992Co-Authors: Claus Siebe, Jean-christophe Komorowski, Michael F SheridanAbstract:A pre-historic collapse of the northeastern flank of Jocotitlan Volcano (3950 m), located in the central part of the Trans Mexican Volcanic Belt, produced a Debris-Avalanche deposit characterized by surficial hummocks of exceptional size and conical shape. The Avalanche covered an area of 80 km2, had an apparent coefficient of friction (H/L)_of 0.11, a maximum runout distance of 12 km, and an estimated volume of 2.8 km3. The most remarkable features of the Jocotitlan Debris Avalanche deposit are: the several steep (29–32°) conical proximal hummocks (up to 165 m high), large tansverse ridges (up to 205 m high and 2.7 km long) situated at the base of the volcano, and the steep 15–50 m thick terminal scarp. Proximal conical hummocks and parallel ridges that can be visually fitted back to their pre-collapse position on the mountain resulted from a sliding mode of emplacement. Steep primary slopes developed as a result of the accumulation of coarse angular clasts at the angle of repose around core clasts that are decameters in size. Distal hummocks are commonly smaller, less conical, and clustered with more diffuse outlines. Field evidence indicates that the leading distal edge of the Avalanche spilled around certain topographic barriers and that the distal moving mass had a yield strength prior to stopping. In the NE sector, the Avalanche was suddenly confined by topographically higher lacustrine and volcaniclastic deposits which as a result were intensely thrust-faulted, folded, and impacted by large clasts that separated from the Avalanche front. Post-emplacement loading also induced normal faulting of these soft, locally water-rich sediments. The regional tectonic pattern, N-NE direction of flank failure, and the presence of a major normal fault which intersects the volcano and is parallel to the orientation of the Acambay graben located 10 km to the N suggest a genetic relationship between the extensional tectonic stress regime and triggering of catastrophic slope failure. The presence of a 3-m-thick sequence of pumice and obsidian-rich pyroclastic surge and fall tephra directly overlying the Debris-Avalanche deposit indicates that magma must have been present within the edifice just prior to the catastrophic flank failure. The breached crater left by the Avalanche has mostly been filled by dacitic domes and lava flows. The youngest pryroclastic surge deposits on the upper flanks of the volcano have an historical C14 age of 680±80 yearsBp (Ad 1270±80). Thus Jocotitlan volcano, formerly believed to be extinct, should be considered potentially active. Because of its close proximity to Mexico-City (60 km), the most populous city in the world, reactivation could engender severe hazards.
