INSIVUMEH reported that on 29 September a lahar 28 m wide and 2 m deep traveled down Santa María's Rio Nima II drainage, carrying 2-m-wide blocks and tree branches. During 29-30 September and 3-4 October explosions from the Santiaguito lava dome complex produced gray ash plumes that rose 1 km above the crater and drifted 15 km E and SW. Avalanches from the lava-flow fronts descended the flanks. During 3-4 October avalanches from the lava dome occasionally generated pyroclastic flows; lava flows were active on the SW and SE flanks.

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)