Ash and gas eruptions from Caliente vent occurred irregularly over the 3-day period of observation, with intervals of 1/2-4 hours between eruptions. Most eruptions lasted 2-3 minutes and sent ash and gas columns to heights of several hundred meters to 1 km above the vent. Five mm of ash accumulated at the foot of the dome over one 12-hour period. Eruptions occasionally threw 10-cm blocks several hundred meters and ejected tephra to well above the summit of Santa María. Although not directly observed, the plug dome and blocky lava flow that were seen being extruded from Caliente vent in February were apparently still very active. Large avalanches of glassy material could be heard from Caliente vista many times per hour. Debris from these avalanches was visible in the barranca below Santiaguito.

Geological Summary. Symmetrical, forest-covered Santa María volcano is part of a chain of large stratovolcanoes that rise above the Pacific coastal plain of Guatemala. The sharp-topped, conical profile is cut on the SW flank by a 1.5-km-wide crater. The oval-shaped crater extends from just below the summit to the lower flank, and was formed during a catastrophic eruption in 1902. The renowned Plinian eruption of 1902 that devastated much of SW Guatemala followed a long repose period after construction of the large basaltic-andesite stratovolcano. The massive dacitic Santiaguito lava-dome complex has been growing at the base of the 1902 crater since 1922. Compound dome growth at Santiaguito has occurred episodically from four vents, with activity progressing E towards the most recent, Caliente. Dome growth has been accompanied by almost continuous minor explosions, with periodic lava extrusion, larger explosions, pyroclastic flows, and lahars.

Information Contacts: R. Stoiber, S. Williams, R. Naslund, M. Conrad, and L. Malinconico, Dartmouth College; S. Bonis, Instituto Geográfico Nacional (IGN); A. Aburto and D. Fajardo, Instituto de Investigaciones Sísmicas, Nicaragua.