Post-depositional fracturing and subsidence of pumice flow deposits: Lascar Volcano, Chile

• DOI: 10.1007/s00445-011-0545-1
• Publication Date: 2011-09-26T10:36:10Z
• Authors: Patrick L. Whelley; J. Jay; E. S. Calder; M. E. Pritchard; N. J. Cassidy; S. Alcaraz; A. Pavez
• Keywords: Lithology; Pumice

Unconsolidated pyroclastic flow deposits of the 1993 eruption Lascar Volcano, Chile, have, with time, become increasingly dissected by a network deeply penetrating fractures. The fracture comprises orthogonal sets decimeter-wide linear voids that form pseudo-polygonal grid visible on deposit surface. In this work, we combine shallow surface geophysical imaging tools remote sensing observations and direct field measurements to investigate these fractures their underlying causal mechanisms. Based ground radar images, are observed have propagated depths up 10 m. addition, orbiting interferometry shows subsidence 1 cm/year-1 occurred between 1996 continued occurring at slower rate thereafter. situ show m below surface, remain 5°C 15°C hotter, 18 years after emplacement, than adjacent deposits. as well estimated cooling rates, inferred be combined result deaeration, thermal contraction, sedimentary compaction in months following deposition. Significant environmental factors, including regional earthquakes 1995 2007, accelerated settling punctuated moments time. spatially variable pattern relates slope lithofacies variations substrate lithology. Similar been reported other ignimbrites but generally exposed only cross section often attributed formation external forces. Here suggest such interpretations should invoked caution, deformation post-emplacement fracturing loosely packed ash-rich is process inherent material.