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Volcanic Debris Avalanches : Introduction and Book Structure
No full textVolcanic debris avalanches (VDA) are, on the one hand, stunning natural phenomena, but, on the other, can pose serious threats to people and infrastructure. This first chapter aims to introduce a collection of themed papers gathered in a book, each illustrating the advancements of a different aspect of VDA research. As a state-of-the-art collection, the 11 papers provide a powerful tool for the volcanological community to enhance our understanding of their history and global distribution, collapse initiation and cyclic occurrence, problems with terminology, transport processes and deposit characteristics, climate impacts, application of numerical tools, and the records of marine and ringplain settings
Unusual volcanic instability and sector collapse configuration at Chimpa volcano, central Andes
No full textUpper 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.Fil: Norini, Gianluca. Consiglio Nazionale delle Ricerche; Italia. Istituto di Geologia Ambientale e Geoingegneria; ItaliaFil: Bustos, Emilce. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; ArgentinaFil: Arnosio, José Marcelo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; ArgentinaFil: Baez, Walter Ariel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; ArgentinaFil: Zuluaga, María Clara. Servicio Geologico Colombiano.; ColombiaFil: Roverato, Matteo. Yachay Tech University; Ecuado
Volcaniclastic lacustrine sedimentation in the Pleistocene Guayllabamba intermontane basin in the Ecuadorian Andes
No full textIn this work, we present a description of the sedimentary fill of a well-exposed lacustrine succession
in the Ecuadorian Andes. The Guayllabamba basin is an intermontane basin located in the Andean range of
Ecuador, and part of its sedimentary history is represented by a volcanically influenced c. 100 m-thick lacustrine
unit of Pleistocene age. We create a stratigraphic cross-section from the eastern to western lake margins and
identify 19 facies that were used to carry out a palaeoenvironmental reconstruction. The Guayllabamba palaeolake
was developed in a tectonic depression surrounded by volcanoes and it was filled with sediments derived
from the erosion of the volcanic edifices, the reworking of unconsolidated pyroclastic deposits and deposition of
pyroclastic currents into the lake. The lake shows a deepening trend, passing from shallow deltaic sedimentation
to varved diatomites with turbidites. Abundant ash-fall beds, monolithological pumiceous deltaic sequences and
pumice-dominated thick ignimbrites show the impacts of volcanism on lacustrine sedimentation within this
basin. Soft-sediment deformation and gravity flow deposits are common owing to the intrabasinal tectonic
activity and to the intrusion of a lava body. Aulacoseira-rich diatomites dominate the background lake sedimentation.
The outcrops of the Guayllabamba basin are outstanding examples of the interaction between volcaniclastic
and lacustrine sedimentation
A Historical Perspective on Lateral Collapse and Volcanic Debris Avalanches
No full textIn 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
Evidence of the Early Holocene eruptive activity of Volcán de Colima and the 8.2 kyr global climatic event in lacustrine sediments from a debris avalanche-dammed lake
Full text linkVolcán de Colima, one of the most active volcanoes in Mexico, experienced at least nine flank failures
during the last 30 000 years, with catastrophic effects on the environment that implies the formation of temporary
dams where lacustrine sediments accumulated for hundreds of years. These lacustrine sequences
preserve an exceptional record from which to reconstruct the effect of subsequent volcanic eruptions and, eventually,
contemporary environmental and climatic conditions. Here we analyse an Early Holocene lacustrine
sequence, named ‘Gypsum King’, which accumulated in a short-lived temporary lake, likely formed by
emplacement of the 10 755–11 230 cal years BP Mesa-Yerbabuena debris avalanche. Through detailed analysis
of the 1.8 m thick lacustrine sequence (14C ages, sulfur content, grain size), it was possible to identify the 8.2 kyr
global climate event and better constrain the Early Holocene main sub-plinian to plinian eruptions of Volcán de
Colima. The results presented here highlight the potential to explore sulfur content and abrupt change in grain
size in lacustrine sediments as additional proxies to better constrain eruptive phases in volcanic environments.
Finally, the Gypsum King sequence provides the first evidence of the 8.2 kyr global climate event along the
Eastern tropical Pacific Coast
Grain size distribution and sedimentology in volcanic mass-wasting flows: implications for propagation and mobility
Full text linkThe sedimentological characteristics of mass-wasting flow deposits are important for assessing the differences between phenomena and their propagation and emplacement mechanisms. In the present study, nine volcanic debris avalanche deposits and eight lahar deposits are considered, from the literature. Their sedimentology is expressed in the descriptive statistics: median grain size, sand, gravel and finer particle fractions, skewness and sorting. Analysis of the data confirms that lahars and debris avalanches diverge in their grain size distribution and in their evolution during propagation. Water saturation in lahars is the main factor enabling debulking, a mechanism that is not recorded in the data derived from debris avalanches deposits. On the contrary, evidence of comminution of particles due to particle-particle interactions is observed in debris avalanches, and not in lahars. These findings support previous studies suggesting that although water content in debris avalanches plays a role in propagation, the effects of inertial collision of solid fragments are more important than fluid effects, confirming that particle-particle interactions are the main factor influencing the mobility of non-saturated mass wasting flows
Paleoproterozoic andesitic volcanism in the southern Amazonian craton, the Sobreiro Formation: New insights from lithofacies analysis of the volcaniclastic sequences
No full textThe Sobreiro Formation (SF) records one excellent and well-preserved example of subaerial Precambrian (ca. 1.88 Ga) volcanism on earth. It is located in the Sao Felix do Xingu region (SFX), in the eastern part of Path State, southern Amazonian craton, northern of Brazil. The high-K calcalkaline composition of the Sobreiro rocks indicates that this formation likely generated in an ocean-continent convergent margin. This paper documents the architecture of a series of basaltic-andesite to andesite and minor dacite lava flows and associated volcaniclastic rocks. These rocks are divided into primary and secondary lithotypes, depending if they resulted from a direct volcanic activity (pyroclastic) or reworked processes and massive to stratified, depending on the different transport and emplacement mechanisms. Primary lithofacies is formed of pyroclastic flow and surge deposits, volcanic breccias and welded ignimbrites; secondary volcaniclastic lithofacies consist of reworked debris. Mass-flows, hyperconcentrated flows and stream floods are interpreted as fluvial/alluvial deposits representing periods of stream and river reworking and re-establishment after an eruptive phase or an edifice failure event. These different lithofacies record the volcanic history of the Sobreiro Formation. A complex volcanic environment is thought to have existed with emission of large lava flows and explosive eruptions. The modern volcanological approach used here can serve as a model for the evolution of Precambrian volcano-sedimentary basins. Our approach sheds new light on the different processes operating on volcanic edifices and to constrain the depositional environment and thus geodynamic setting of Precambrian continental volcanic belts. (C) 2016 Elsevier B.V. All rights reserved
Geomorphometric comparative analysis of Latin-American volcanoes
No full textThe geomorphometric classifications of three groups of volcanoes situated in the Andes Cordillera, Central America, and Mexico are performed and compared. Input data are eight local topographic gradients (i.e. elevation differences) obtained by processing each volcano raster ASTER-GDEM data. The pixels of each volcano DEM have been classified into 17 classes through a K-means clustering procedure following principal component analysis of the gradients. The spatial distribution of the classes, representing homogeneous terrain units, is shown on thematic colour maps, where colours are assigned according to mean slope and aspect class values. The interpretation of the geomorphometric classification of the volcanoes is based on the statistics of both gradients and morphometric parameters (slope, aspect and elevation). The latter were used for a comparison of the volcanoes, performed through classes' slope/aspect scatterplots and multidimensional methods. In this paper, we apply the mentioned methodology on 21 volcanoes, randomly chosen from Mexico to Patagonia, to show how it may contribute to detect geomorphological similarities and differences among them. As such, both its descriptive and graphical abilities may be a useful complement to future volcanological studies. (C) 2017 Elsevier Ltd. All rights reserved
Volcanic Debris Avalanche Transport and Emplacement Mechanisms
No full textField 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.</p
Characterization of the Cubilche debris avalanche deposit, a controversial case from the northern Andes, Ecuador
No full textIn areas characterized by many volcanoes, identifying the source of a deposit may not be trivial. This becomes much more complicated when looking for the source of a debris avalanche deposit (DAD), the common products of catastrophic volcanic edifice collapses. To overcome this problem, in this work a methodology is proposed based on the integration of texture features and areal distribution of the deposit, comparison between the petrography of the coarser clasts within the DAD and of the proximal products, grain-size analysis, and the volumetric estimations of the deposit and the volume missing from the volcanic edifice. This methodology has been tested to a DAD occurred near the city of Ibarra (Imbabura Province; Northern Ecuador), having a controversial source. Two main volcanic edifice are located in proximity of the DAD, the Cubilche volcano (3826 m.a.s.l.), located immediately south of and east of the colossal dormant Imbabura volcano. The former displays a sharp horseshoe-shaped scar towards the north and inside this post-collapse edifice, that we name old Cubilche volcano (OCV), is located the young Cubilche volcano (YCV) that refilled a portion of the collapse scar and partially covered the southern flank of the OCV. Detailed knowledge of Cubilche volcano is critical because of its close proximity and interspersed activity with Imbabura volcano. In fact, Imbabura most recent edifice was built over the northwestern slope of the OCV and partially covered it. Recent studies linked the studied DAD to both Imbabura volcano as a product of its northern sector collapse, as well as neighboring Cubilche volcano. Our data points to Cubilche as the most likely source for this DAD. A perspective view of the shaded relief image of the present day OCV shows that the morphology of the volcano is well-preserved on its southern, eastern, and western flanks. This allows us to reconstruct the morphology of the OCV previous to the collapse through interpolation of elevation and altitude data of preserved flanks. A DEM of the present day topography was used for extrapolating the morphology. Using similar methodology, the post collapse base of the amphitheater was reconstructed by removing the relief of the present day YCV. The reconstructed topography of the OCV shows that it could have been a symmetric cone, reaching a maximum elevation of ~4100 m.a.s.l. with a lack volume of ~3.5 km3. Based on this scenario, the deposit originated from the OCV main collapse should have a volume \u3e 3–3.5 km3 in accordance to the volume calculated for the studied DAD
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