Dune bedforms produced by dilute pyroclastic density currents from the August 2006 eruption of Tungurahua volcano, Ecuad
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RESEARCH ARTICLE
Dune bedforms produced by dilute pyroclastic density currents from the August 2006 eruption of Tungurahua volcano, Ecuador Guilhem Amin Douillet & Daniel Alejandro Pacheco & Ulrich Kueppers & Jean Letort & Ève Tsang-Hin-Sun & Jorge Bustillos & Minard Hall & Patricio Ramón & Donald B. Dingwell
Received: 17 February 2013 / Accepted: 17 September 2013 / Published online: 13 October 2013 # The Author(s) 2013. This article is published with open access at Springerlink.com
Abstract A series of pyroclastic density currents were generated at Tungurahua volcano (Ecuador) during a period of heightened activity in August 2006. Dense pyroclastic flows were confined to valleys of the drainage network, while dilute pyroclastic density currents overflowed on interfluves where they deposited isolated bodies comprising dune bedforms of cross-stratified ash exposed on the surface. Here, the description, measurement, and classification of more than 300 dune bedforms are presented. Four types of dune bedforms are identified with respect to their shape, internal structure, and geometry (length, width, thickness, stoss and lee face angles, and stoss face length). (1) “Elongate dune bedforms” have smooth shapes and are longer (in the flow direction) than wide Editorial responsibility: V. Manville Electronic supplementary material The online version of this article (doi:10.1007/s00445-013-0762-x) contains supplementary material, which is available to authorized users. G. A. Douillet (*) : U. Kueppers : D. B. Dingwell Earth & Environmental Sciences, Ludwig-Maximilians-Universität (LMU), Munich, Germany e-mail: [email protected] D. A. Pacheco : J. Bustillos : M. Hall : P. Ramón Instituto Geofísico, Escuela Politécnica Nacional, Quito, Ecuador J. Letort : È. Tsang-Hin-Sun Ecole et Observatoire des Sciences de la Terre, Université de Strasbourg, Strasbourg, France J. Letort Laboratoire de Géophysique Interne et Tectonophysique (LGIT), Grenoble, France È. Tsang-Hin-Sun Laboratoire de Géosciences Marines, Université de Brest, Brest, France
or thick. Internal stratification consists of stoss-constructional, thick lensoidal layers of massive and coarse-grained material, alternating with bedsets of fine laminae that deposit continuously on both stoss and lee sides forming aggrading structures with upstream migration of the crests. (2) “Transverse dune bedforms” show linear crests perpendicular to the flow direction, with equivalent lengths and widths. Internally, these bedforms exhibit finely stratified bedsets of aggrading ash laminae with upstream crest migration. Steep truncations of the bedsets are visible on the stoss side only. (3) “Lunate dune bedforms” display a barchanoidal shape and have stratification patterns similar to those of the transverse ones. Finally, (4) “two-dimensional dune bedforms” are much wider than long, exhibit linear crests and are organized into trains. Elongate dune bedforms are found exclusively in proximal deposition zones. Transverse, lunate, and two-dimensional dune bedforms are
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