Abstract

From 1990 to 2004, four cycles of dome growth and explosive dome destruction occurred at the Colima volcano. In this paper, we describe these cycles, focusing on the seismic characteristics of the last three cycles from 1997 and 2004, for which we have the best data. Four episodes of dome building occurred: from early 1991 to late 1992, from November 1998 into January 1999, from November 2001 through February 2003, and from September 2004 into 2005. The rate of extrusion during these episodes ranged from a low-extrusion rate accompanied by seismicity and evolved with time to a high rate of aseismic extrusion for the last episode in 2004. The first of these four extrusive episodes was followed by dome-destroying explosions in July 1994. The second extrusive episode was followed by four dome-destroying explosions over six months and a fifth explosion 17 months later, while the third extrusive episode was followed by three dome-destroying explosions over two months. A fourth extrusive episode began in 2004. The nature of each explosion was somewhat different. For each of the explosions, we compare the total seismic energy released (1) during the hours prior to each explosion, (2) during each explosion, and (3) during the hours after each explosion. We also propose an additional method for classifying the explosions based on coupled acoustic waves and describe characteristics of the volcanic earthquakes recorded. We use data from the 10 May 1999 explosion to construct a new P-wave velocity model for the upper structure of the volcano.

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