HR: 1340h
AN: V33B-0679    [Abstracts]
TI: The Costa Rican Central Valley Lavina Formation: Lahar or Debris Avalanche?
AU: * Hidalgo, P J
EM: hidalgop@msu.edu
AF: Michigan State University, Department of Geological Sciences 206 Natural Science Building, East Lansing, MI 48824-1115 United States
AU: Alvarado Induni, G E
EM: galvaradoi@ice.go.cr
AF: Instituto Costarricense de Electricidad, ICE Aptdo Dept. Geologia, San Jose, SJ 10032-100 Costa Rica
AU: Linkimer, L
EM: linkime1@msu.edu
AF: Michigan State University, Department of Geological Sciences 206 Natural Science Building, East Lansing, MI 48824-1115 United States
AB: The Lavina Formation of the Central Valley of Costa Rica consists of lava blocks floating in a volcanic mud matrix. Different authors have interpreted this deposit genetically as a lahar or debris flow deposit. Based on geomorphologic, textural, and morphometric evidence, we conclude that the origin of this deposit is a debris avalanche event that transformed into a debris flow on its path down the valley. Using aerial photographs, many debris avalanche amphitheaters are found in the western sector of the Irazu volcanic complex. However, textural and morphometric characteristics of the deposit are consistent with the source of the sector collapse being located on the west flank of the Cabeza de Vaca volcano. Three-dimensional modeling of the Lavina Formation was done using data from 213 drill cores distributed along the Central Valley area. Maps of isopaches and isohipses of the roof and floor of this stratum were created. These allowed for qualification of morphometry of the stratigraphic surfaces, characterization of the paleoslopes, and quantification of the compacted deposit volume. The data derived form the isopach and isohipse contour maps indicate that abrupt changes in the thickness of the stratum are common. Also, it illustrates the morphological differences between the roof, elongated hills in the direction of the flux, and the floor of the stratum, smooth and uniform. The morphometric, geomorphologic, and textural evidence, were used to conclude that the Lavina deposit originated as a debris avalanche event in the Cabeza de Vaca Volcano. The debris avalanche was eventually fluidized into a debris flow that spread extensively (130 km²) along the Central Valley of Costa Rica.
DE: 8485 Remote sensing of volcanoes
DE: 8488 Volcanic hazards and risks
DE: 8494 Instruments and techniques
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005