HR: 11:50h
AN: V42B-06    [Abstracts]
TI: Characteristics of a Small, Rain-Generated, Ash-Rich Lahar, Volcan Tungurahua, Ecuador
AU: * Stinton, A J
EM: astinton@geology.buffalo.edu
AF: Department of Geology, University at Buffalo, 876 Natural Sciences, Buffalo, NY 14260 United States
AU: Williams, R
EM: rw32@buffalo.edu
AF: Department of Geology, University at Buffalo, 876 Natural Sciences, Buffalo, NY 14260 United States
AU: Sheridan, M F
EM: mfs@eng.buffalo.edu
AF: Department of Geology, University at Buffalo, 876 Natural Sciences, Buffalo, NY 14260 United States
AB: Prolonged activity at Volcán Tungurahua, Ecuador, has been characterized by small to moderate eruptions that have deposited ash on the steep upper flanks of the volcano. Remobilization of the ash by rain has resulted in the generation of many small to moderate sized lahars in drainages on the northern flanks. On February 12, 2005, a small lahar traveled down the 10 km length of the Vazcún Valley on the north-east flank of the volcano. This flow was recorded by both the seismic and Acoustic Flow Monitoring (AFM) stations and was captured on video and in photographs by Defensa Civil officials from the city of Baños. These sources, along with additional pre- and post-event photographs and GPS mapping of the channel have allowed for a detailed study into the flow dynamics and geomorphic effects of a small lahar. Seismic and AFM recordings indicate two flow pulses, while field evidence (e.g., deposit stratigraphy, photographs and video) suggest at least four or more flow pulses in some sections of the channel. Velocities estimated from superelevation around bends and travel time between seismic and AFM stations, and eyewitness locations are less than 10 m/sec. Deposition occurred where the valley gradient was low or downstream of constrictions and geomorphic changes due to deposition and erosion are on the order of several decimeters. This lahar is typical of those that have occurred at Volcán Tungurahua during its current eruptive period, and despite its small size, has provided a unique opportunity to investigate in detail lahar flow dynamics.
DE: 1810 Debris flow and landslides
DE: 8404 Volcanoclastic deposits
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005