2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 1
Presentation Time: 1:30 PM


WILLIAMS, Stanley N., Department of Geological Sciences, Arizona State University, Tempe, AZ 85287 1404, stanley.williams@asu.edu

On November 13, 1985, a small volume explosive eruption of the volcano Nevado del Ruiz, Colombia, took place at about 21:30 local time. The initial plinian eruption was followed by eruptions of pyroclastic flows that melted a portion of the glaciers. Resultant mudflows (lahars) traveled up to 80 km from the 5,400 m summit. Approximately 23,000 people were killed while few survived because the lahars destroyed virtually the city of Armero and several smaller settlements. When one debouched from the Rio Lagunilla canyon, 1.5 km west of Armero, two hours after the eruption, it was approximately 45 m high and flowing at 10 m s-1.

Activity following the eruption was very different from that of the major eruption of Mt. St. Helens on May 18, 1980. Flux of the magmatic gas, SO2, increased and remained at the very high level of 1,000s t d-1, usually associated with eruptive activity. By May, 1986 there was such frequent and intense seismicity, including harmonic tremor, that it was considered almost certain that explosive eruptions would occur. Several did but they were of only minor energy and volume. However, in September, 1989, a second magmatic eruption occurred though it was of much less devastation than that of November, 1985.

Although there had not been significant research of the Colombian volcanoes, the reactivation had been recognized more than one year prior to the tragic event. Colombian scientists began their own studies and because of their invitations were joined by colleagues from several countries. Despite their good work and recognition of serious danger they were not able to forecast the eruption or persuade local authorities of the need for education of the general public.

Volcanic activity of Ruiz continues, with a swarm of 1,300 of volcano-tectonic earthquakes over only 16 hours, on June 9, 2002. That activity continued for 3 days, with many earthquakes felt by people near the volcano and the odor of SO2 reported near the summit.

When reviewing studies, from many different perspectives, of the current activity and eruptions prior to that of 1985, it has been possible for us to have recognized and learned a great deal. I will review some of the insights made possible by virtue of many scientists. Volcanology makes almost of its most significant steps of progress on the heels of deadly eruptions, with Ruiz being a classic example.