A synthesis of the recent activity of Galeras volcano, Colombia: Seven years of continuous surveillance, 1989–1995

The current period of re-activation since 1988 at Galeras volcano, Colombia, has been characterized mainly by the following events: (1) a semi-continuous series of Vulcanian eruptions during 5–9 May 1989; (2) emplacement of an andesitic lava dome at the bottom of the main crater in October–November 1991; (3) six vulcanian eruptions during 1992–1993, the first of which destroyed most of the dome on 16 July 1992; and (4) three volcano-tectonic seismic crises in April 1993, November–December 1993 and March 1995. During much of this seven-year period, several small ash and gas emissions also have taken place. The 4–9 May 1989 eruptions originated from the secondary crater El Pinta and deposited ash, lapilli and blocks in the crater area. The 1992–1993 eruptions originated from the main crater and were associated with obstruction of the conduit by magma from dome emplacement in late 1991, causing overpressurization of the system. For the 1992–1993 eruptions, pre-eruptive seismicity, deformation and SO2 flux all exhibited very low levels. The eruptions were characterized by their sudden initiation, low intensity (VEI = 1), small eruption columns, and small volumes of erupted material. The source of the volcano-tectonic seismic crises is located approximately 3 km north and northeast of the crater. Some of these events were felt in Pasto and other towns located around the volcano, on one occasion causing loss of life, injuries and damage to buildings.