On 31 May, rain-induced mudflows caused flash floods on the Nimá II and Tambor rivers, affecting the S flank town of El Palmar. No casualties were reported.

Mudflows and floods have been a persistent problem for S-flank residents. In 1978, blocks and ash from Santiaguito dammed three rivers, forming a large lake. Failure of the debris dam caused damaging mudflows in July and another mudflow in September killed one person. An overflow of the Nimá River forced the evacuation of hundreds of people in August 1982. The 1983 rainy season saw more mudflows and evacuations in the same river valleys. Debris from an eruption on 1 December 1986 blocked two rivers and caused floods in several villages.

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: E. Sánchez, Edgar Quévec, and Enrique Molina, INSIVUMEH.