HR: 1340h
AN: V53B-1556    [Abstracts]
TI: Volcan Reventador's Unusual Umbrella
AU: Chakraborty, P
EM: pinaki@kiddo.tam.uiuc.edu
AF: University of Illinois, 1301 W. Green St., Urbana, Il 61801 United States
AU: Gioia, G
EM: ggioia@uiuc.edu
AF: University of Illinois, 1301 W. Green St., Urbana, Il 61801 United States
AU: * Kieffer, S W
EM: skieffer@uiuc.edu
AF: University of Illinois, 1301 W. Green St., Urbana, Il 61801 United States
AB: In the past two decades, field observations of the deposits of volcanoes have been supplemented by systemmatic, and sometimes, opportunistic photographic documentation. Two photographs of the umbrella of the December 3, 2002 eruption of Volcan Reventador, Ecuador, reveal a prominently scalloped umbrella that is unlike any umbrella previously documented on a volcanic column. The material in the umbrella was being swept off a descending pyroclastic flow, and was, therefore, a co-ignimbrite cloud. We propose that the scallops are the result of a turbulent Rayleigh-Taylor (RT) instability with no precedents in volcanology. We ascribe the rare loss of buoyancy that drives this instability to the fact that the Reventador column fed on a cool co-ignimbrite cloud. On the basis of the observed wavelength of the scallops, we estimate a value for the eddy viscosity of the umbrella of 4000 ~m²/s. This value is consistent with a previously obtained lower bound (200 ~m²/s, K. Wohletz, priv. comm., 2005). We do not know the fate of the material in the umbrella subsequent to the photos. The analysis suggests that the umbrella was negatively buoyant. Field work on the co-ignimbrite deposits might reveal whether or not the material reimpacted, and if so, where and whether or not this material was involved in the hazardous flows that affected the main oil pipeline across Ecuador.
DE: 8414 Eruption mechanisms and flow emplacement
DE: 8425 Effusive volcanism
DE: 8428 Explosive volcanism
DE: 8486 Field relationships (1090, 3690)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005