HR: 1340h
AN: V13D-0571    [Abstracts]
TI: Paleoenvironment Reconstructions on the Cerro Blanco Subcomplex of Nevados de Chillan Volcano, Chile Using Volcanic Facies.
AU: Gilbert, J S
EM: j.s.gilbert@lancaster.ac.uk
AF: Department of Environmental Science, Lancaster University, Lancaster, LA1 4YQ United Kingdom
AU: * Mee, K
EM: katymee@hotmail.co.uk
AF: Department of Environmental Science, Lancaster University, Lancaster, LA1 4YQ United Kingdom
AU: Tuffen, H
EM: h.tuffen@lancaster.ac.uk
AF: Department of Environmental Science, Lancaster University, Lancaster, LA1 4YQ United Kingdom
AB: Nevados de Chillán stratovolcano, central Chile has been active since at least 640 ka and continues to be active at present day. Eruptions have occurred during glacial and non-glacial periods meaning that interactions between volcanic products and snow and ice are common. Detailed studies of the volcanic textures found on the Cerro Blanco subcomplex of Nevados de Chillán volcano have enabled reconstructions of former eruptive environments including interpretations of thicknesses and extents of ice and snow at the time of eruption. Steep-fronted, glassy lava lobes surrounded by hyaloclastite, erupted on the western flank of Cerro Blanco, are thought to have been intruded into ice, causing rapid cooling and impeding further advancement of the lava. More recently, the andesitic Santa Gertrudis lava was erupted from a cone on the northwest flank of Cerro Blanco during the winter of 1861. The lava exhibits features typical of subaerial cooling although arcuate fractures on the base and margins of the first erupted lavas are interpreted as snow-contact features formed when steam generated from melting snow entered tensional fractures at the flow base. Similar textures found in conjunction with subaerial and ice-contact features, within a 90.0 ± 0.6 ka old lava flow emplaced on the northwest flank of Cerro Blanco, are inferred to also be snow-contact features. These textures have been used to infer that a small valley glacier, overlain by snow, existed in the Santa Gertrudis Valley at the time of the eruption. Such reconstructions are important for determining the long-term environmental evolution of the volcano as well as assessing future hazards at seasonally snow-covered volcanoes.
DE: 8408 Volcano/climate interactions (1605, 3309)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005