HR: 1340h
AN: V33A-0678    [Abstracts]
TI: Uncertainties in Probability Calculations of Future Fatal Eruptions at Arenal Volcano, Costa Rica, a Favorite Tourist Destination
AU: * Melson, W G
EM: melsonw@nmnh.si.edu
AF: Smihsonian Institution, NHB 119, Washington, DC 22652-0119 United States
AU: Barquero, J
EM: jabarque@rasca,co,cr
AF: Volcanologist, Apartado 5-2400 Desamparados, San Jose, 5-2400 Costa Rica
AB: Calculation of the probability of future fatalities at Arenal Volcano involves two independent terms: the probability at any time interval of eruptions with potentially fatal consequences and the probability of someone being in a hazardous zone at the time of such an eruption. A near-crater ejected block killed a tourist in 1987 and a pyroclastic flow killed a tourist and guide in 2000. Creation of Arenal National Park has helped control access to the southwest slopes. Between 1987 and 1994, Earthwatch and Smithsonian volunteers recorded 8067 pyroclastic eruptions over 189 days of continuous observations in 15 ca. two-week time slices. 3246 explosions ejected blocks within a few hundreds of meters (common) up to 2000 m (rare) from the summit crater(s), giving an average of 17 explosions/day, ranging greatly though from one tome slice to another. Over the past 18 years, the frequency of pyroclastic events has decreased punctuated by a few periods of increased frequency. Over the past 37 years, there have been two fatal pyroclastic flows, giving an average rate of .05 fatal pf/yr. Data from 1994 to the present from a seismic and acoustic automatic data acquisition system (ADAS) 2.8 km south of the summit at the Arenal Observatory Lodge reveal no detected precursors to the August 23, 2000 fatal pyroclastic flow. Growing summit pyroclastic cones now pose additional risk through collapse that can produce hot avalanches. Pyroclastic event counts versus magnitude from field observations and ADAS reveal linear trends on log-log plots that are indicative of self-organized critical systems. Although difficult to rigorously quantify, the probability of fatal volcanic events remains of concern at Arenal.
DE: 8419 Volcano monitoring (7280)
DE: 8425 Effusive volcanism
DE: 8428 Explosive volcanism
DE: 8488 Volcanic hazards and risks
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005