Arreygue, E.

Canuti, Paolo

Falorni, Giacomo

Garduno, V.

Gigli, Giovanni

Morelli, Stefano

English

Florence Research

Geophysical Research Abstracts, Vol. 8, 08787, 2006SRef-ID: 1607-7962/gra/EGU06-A-08787© European Geosciences Union 2006Field investigation and modelling of a huge debrisavalanche from Tancitaro Volcano (Mexico)S. Morelli(1), G. Gigli(1), G. Falorni(1), V. Garduño(2), E. Arreygue(2), P. Canuti(1)(1) Earth Sciences Department, University of Firenze +39 055 2756343 (2) UMSNH-IIM,Departamento de Geologia y Mineralogia, MexicoThe Tancitaro (3840 m) is one of the highest volcanoes of the central portion of theMexican Volcanic Belt. It is located in the SW sector of the Tarascan corridor, wheretwo important types of volcanoes of quaternary age are observed: a single collapsedcomposite volcano (Tancitaro) surrounded by a field of monogenetic cinder cones.The distribution of the cinder cones is controlled by NE-SW faults, although there arealso additional faults with NNW-SSE trends along which some cones are aligned. TheTancitaro stratovolcano is located at the intersection of the NW-SE and NE-SW struc-tures. The Tancitaro is composed of andesitic to dacitic layers. From a morphologicalstandpoint the volcano is characterized by U-shaped, glacially incised valleys, cut byan east-facing horseshoe-shaped crater. This collapse structure (4 km wide and 5.3 kmlong) is related with a large fan that was deposited within the Tepalcatepec depressionstarting only 7 km downslope from the failure scar. The fan was primarily formed bythe deposit of this huge debris avalanche (˜ 18 km3) and subsequently by fluvial anddebris flow deposits. It is 66 km long and covers an area of approximately 1155 km2.Field investigations on the fan area highlighted the presence of typical debrisavalanche hummock morphologies in the proximal area. The hummocks are com-posed of structures ascribable to the so-called “block facies” seen in many other de-bris avalanche deposits (e.g. Capra et al., 2001). In the distal zones, blocks and mega-blocks, some of which are characterized by a jigsaw puzzle texture, gradually decreasein size until they disappear entirely in the most distal reaches; this portion of the de-posit corresponds to the “mixed block and matrix facies” described by Glicken (1996)It was also possible to delimit a time frame for the occurrence of the Tancitaro debrisavalanche by using an expeditious method of relative dating for the monogenic cin-der cones of the area (Peña 1992). By combining this information with absolute datesfrom nearby deposits from previous studies (e.g. Scattolin, 1996) an upper tempo-ral limit of approximately 4000 years was established. A lower limit was ascertainedfrom geomorphologic and climatologic information. In fact, the debris avalanche cutsglacially incised valleys that date back to the most recent glaciological period, whichoccurred approximately 6000 - 10000 years BP. The age of the collapse can there-fore be constrained to between 4000 and 10000 years BP. The comparison betweenthe debris avalanche of the Tancitaro and other great collapses with similar morpho-metric features (vertical relief during runout, travel distance, volume and area of thedeposit) indicate that the collapse was most likely not primed by any type of eruption,but rather triggered by a strong seismic shock that could have induced the failure of aportion of the edifice, already deeply altered by intense hydrothermal fluid circulation.It is also possible to hypothesize that mechanical fluidization (Hungr, 1990) may havebeen the mechanism controlling the long runout of the avalanche, as has been docu-mented for other well-known events. The behavior of the Tancitaro debris avalanchewas numerically modeled using the DAN code (Hungr, 1995). By opportunely modi-fying the rheological parameters of the different models selectable within DAN, it wasdetermined that the two-parameter “Voellmy model” provides the best approximationof the avalanche movement. The Voellmy model produces the most realistic results interms of runout distance, velocity and spatial distribution of the failed mass. It shouldbe noted that although the Tancitaro event was not witnessed directly, it is possibleto infer approximate velocities and overall dynamic behavior from comparisons withsimilar events, namely the Mt. St. Helens debris avalanche of 18 May 1980.

Field investigation and modeling of a huge debris avalanche from Tancitaro Volcano (Mexico)

https://flore.unifi.it/bitstream/2158/385228/1/Morelli%20et%20al%20GRA%20vol%208%20EGU%202006.pdf

Field investigation and modeling of a huge debris avalanche from Tancitaro Volcano (Mexico)

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