History of Galeras

Elements in the media made the event controversial by suggesting the team leader Stanley Williams, who survived, had ignored safety procedures. A prediction had been made three days before the eruption based on B-Type activity seen on a seismograph. Seismic B-types had been used successfully to predict eruptions on other volcanoes. However, the prediction was based simply on the one seismographic printout viewed in the light of previous history of Galeras, without any additional scientific measurements showing any serious activity within the volcano.

21st-century activity

The Galeras Volcano, aerial image by NASA showing its activity. City of Pasto on the right.

Activity at a low level has continued at Galeras, with small explosions occasionally dusting nearby villages and towns with ash. The volcano has continued to be well studied, and predictions of eruptions at the volcano have improved. One phenomenon, which seems to be a reliable precursor to eruptive activity, is a low-frequency seismic event known as a tornillo event. These have occurred before about four-fifths of the explosions at Galeras, and the number of tornillo events recorded before an eruption is also correlated with the size of the ensuing eruption.

More than 100 minor tremors were felt during a major eruption in April 2002, although no damage or injury was reported. An eruption in November 2005 forced an evacuation of the dangerous area surrounding the volcano, and about 9,400 people from nearby villages (most of them farmers) were