INSIVUMEH reported that eruptive activity continued at Santa Maria’s Santiaguito lava dome complex during 26 September-3 October. Incandescence from Caliente dome was visible during most nights and early mornings, and occasionally from the lava flow on the SW flank. Lava extrusion continued and generated block avalanches on the SW, S, and E flanks. Daily weak-to-moderate explosions generated gas-and-ash plumes that rose 700-1,000 m above the dome and drifted mainly W and SW. Explosions triggered incandescent avalanches that descended the dome’s flanks in all directions. A special bulletin issued at 1300 on 27 September described a hot lahar with a sulfur odor that descended the Zanjón Seco drainage on the SW flank carrying blocks 1-2 m in diameter. About 40 minutes later a viscous lahar descended the Cabello de Ángel river, a tributary of the Nimá I, on the E flank, carrying volcanic blocks up to 1 m in diameter, tree trunks, and branches. During 29-30 September explosions occurred at a rate of 1-2 per hour and produced block-and-ash flows that descended the W and SW flanks and left deposits of gray ash. Block avalanches descended the SW, S, and SE flanks during 30 September-1 October and occasionally produced small pyroclastic flows.

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)