Geological/Geophysical Disasters
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CASE STUDY GALERAS VOLCANO, COLOMBIA Barry Voight1,2, Marta L. Calvache3 1 Penn State University, University Park, PA, USA 2 Cascades Volcano Observatory, Vancouver, WA, USA 3 INGEOMINAS, Bogota, Colombia
Summary points Galeras Volcano, Colombia: Volcano Crises, 1988–2010+: Adverse Impacts without a Major Eruption Lava dome growth with strong seismic, deformation and gas precursors Vulcanian explosions with very subtle precursors and strong shocks Fears of population early in crisis magnified by 1985 Nevado del Ruiz catastrophe Lack of a pre-crisis hazard map led to a chain-reaction of events that culminated in an economic crisis, hostility of authorities and loss of credibility of the scientists Important lessons for safety of volcanologists from 1993 tragedy Continuing difficulty of compliance to evacuation recommendations Introduction Located in southwest Colombia, 4,270-m high Galeras Volcano rises 1,600 m above Pasto, the capital city and economic nucleus of Narino Province (Figure 1). It is the most active volcano in Colombia. Pasto is located on the eastern slope of the volcano, about 7–11 km from the crater. Its population is about 350,000, and over 50,000 more people reside in neighboring villages. Activity at Galeras Volcano extends back about 4,500 years and included six major eruptions before
the most recent episode of activity (Calvache, 2000; Stix et al., 1997). It consists of an active cone some 100–150 m high and 500 m diameter, nested inside a horseshoe-shaped amphitheater created by a prehistoric cone collapse. About 50 periods of unrest have been described in the 500 years of recorded history at Galeras, of which 27 have proceeded into eruptions. Twelve of these episodes were brief and included small explosions, and the remainder were more notable but still modest. Pyroclastic currents of mixtures of blocks, ash, and gas generated by a collapsing eruption column descended beyond the crater rim in 1580, 1616, 1641–43, and 1936, and represent the most serious current potential hazard. The effects on Pasto in historic events include ash deposits of 4 cm or less and shock waves breaking windows. Incandescent ballistic blocks have reached about 3 km from the crater rim. Some building damage and a few fatalities have been caused by strong volcanic earthquakes. The towns of Consaca and Bambona, 12 km west of the active cone, have reported heavier ash falls and stronger earthquakes. Historic loss of life has been limited to tourists and scientists in and near the active cone (Munoz et al., 1993), and several deaths in Pasto due to earthquake-induced building collapse. This case history reviews activity since 1989, and underscores the severe and complex problems that can emerge when no hazards assessments, emergency preparedness plans, or mitigation plans are available at the start of a crisis – such as at Galeras in 1989 and early 1990s. The contribution also examines background information on nine deaths within the crater from an explosion in January 1993.
Post-1988 activity and deadly ex
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