Gabriel A. Reyes

Overview of the 1997^2000 activity of Volcan de Colima, Mexico

Abstract This overview of the 1997–2000 activity of Volcan de Colima is designed to serve as an introduction to the Special Issue and a summary of the detailed studies that follow. New andesitic block lava was first sighted from a helicopter on the morning of 20 November 1998, forming a rapidly growing dome in the summit crater. Numerous antecedents to the appearance of the dome were recognized, starting more than a year in advance, including: (1) pronounced increases in S/Cl and δD values at summit fumaroles in mid-1997; (2) five earthquake swarms between November–December 1997 and October–November 1998, with hypocenters that ranged down to 8 km beneath the summit and became shallower as the eruption approached; (3) steady inflation of the volcano reflected in shortening of geodetic survey line lengths beginning in November–December 1997 and continuing until the start of the eruption; (4) air-borne correlation spectrometer measurements of SO2 that increased from the background values of

The July 1994 episode of seismic activity at Colima Volcano, Mexico

Abstract A new period of seismic activity that culminated in a small phreatic explosion took place in Colima Volcano (Western Mexico) during the month of July 1994. In this note, we present our analysis of this seismicity based upon information from RESCO, the seismic network of the University of Colima. The activity began with a seismic swarm of type A (tectonic-like) earthquakes with epicenters towards the SSW of the summit, followed by shallow low-frequency events underneath the volcanic edifice. The activity was accompanied by landslides and culminated with an explosion that produced small ash falls on the surrounding area. The seismic activity ceased after this episode.