Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH) reported ongoing eruptive activity at Santa Maria’s Santiaguito cone during 16-21 October with continuing lava extrusion at Caliente dome. Daily explosions (a few per hour) generated gas-and-ash plumes that rose as high as 900 m above the summit and drifted mainly NW, S, and SW. Effusion of blocky lava and collapses of material produced block avalanches that descended the flanks. Incandescence was sometimes visible during dark hours from avalanches of material at the dome as well as explosions. Ashfall was reported in San Marcos (8 km SW) on 19 October.

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)