The Instituto Nacional de Sismología, Vulcanología, Meteorología e Hidrología (INSIVUMEH) reported ongoing eruptive activity at Santa Maria’s Santiaguito dome complex during 6-13 May with continuing lava extrusion at Caliente dome. Daily explosions, as many as five per hour when reported, sometimes generated gas-and-ash plumes that rose as high as 1 km above the dome and possibly drifted as far as 15 km E, S, SW, and W. Effusion of blocky lava and collapses of material produced block avalanches that descended multiple flanks; the collapsed material sometimes produced short pyroclastic flows. Incandescence was visible at Caliente dome and upper part of the SW flank lava flow. During the evening of 10 May heavy rainfall generated lahars in the Tambor drainage (SSW) that carried blocks up to 1 m in diameter mixed with fine sediment, tree trunks, and branches. Ashfall was reported in San Marcos (10 km SW), Loma Linda (7 km W), and Palajunoj (17 km SSW) during 12-13 May.

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.

Source: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH)