Many dome collapses took place in late July 1999 when the Caliente crater was the scene of repeated pyroclastic flows. Ash columns rose up to ~2.5 km. Dark beige to gray-colored ash fell ~25 km S in Retalhuleu and some fine ash traveled farther still. Dome extrusions also took place; some relatively fluid lavas traveled towards the S.

When visited on 28-29 December, the volcano's activity consisted of weak explosions. Some of these explosions were accompanied by moderate rumbling, weak avalanches, and sizable, active lava flows descending the S flank. A continuous wind, ~35 km/hour, prevailed in the volcano's vicinity.

During 2137-0919 on 29-30 December observers noted four weak explosions. Two of these, at 2137 and 0419, had associated strong tremor and fine gray ash emissions that rose ~50 m and blew W. Visitors also noted a few weak avalanches.

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: Eddie Sánchez and Otoniel Matías, Instituto Nacional de Sismología, Vulcanología, Meteorología e Hydrología (INSIVUMEH), Ministerio de Communicaciones, Transporte y Obras Publicas, 7A Avenida 14-57, Zona 13, Guatemala City, Guatemala.