Richard Stoiber of Dartmouth College visited the volcano in July, and reported that the Caliente crater was the site of small explosions every 15-60 minutes. Incandescent blocks were thrown up during these small explosive eruptions, which are more or less continuous. Robert Decker noted that the volcano has been active like this for years, but now the explosions seem to be bigger and more regular.

[Rose, in SEAN 02:05, places the start of this increased activity in April 1975.]

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. Decker, Dartmouth College.