BackgroundGaleras is one of Colombia's most frequently active volcanoes. The dominantly andesitic volcano has been active for more than 1 million years, and two major caldera collapse eruptions took place during the past 100,000 years. Several collapse events have produced debris avalanches that swept to the west and left a large horseshoe-shaped caldera inside which the modern cone has been constructed.
Major explosive eruptions in the past thousands of years have produced widespread tephra deposits and pyroclastic flows that swept all but the southern flanks. A central cone slightly lower than the caldera rim has been the site of numerous small-to-moderate historical eruptions since the time of the Spanish conquistadors.
The fatal eruption in 1993
Galeras became active again in 1988 after 10 years of dormancy. It became infamous when it erupted on 14 January 1993, killing six volcanologists and three tourists who were inside the crater when it exploded. The group was part of an scientific conference excursion and their final decision to enter the crater, pushed forth by team leader Stanley Williams (who miracoulously survived), was and still is highly debated: the fatal decision was made despite the observation of a significantly increased number of particular earthquakes (tornillos), which had preceded previous eruptions and also started to occur in the days before the eruption.
See also: Sentinel hub | Landsat 8