INSIVUMEH reported that during 6-7 December incandescence from Santa María's Santiaguito lava-dome complex was visible, and an explosion generated an ash plume that rose 300 m and drifted E. During 8-11 December avalanches were produced from the fronts of lava flows on the SE, S, and SW flanks. A recent lava flow traveled 700 m down the S flank. Ash plumes that rose from the avalanches drifted 10 km W and SW. Crater incandescence was observed at night. A special bulletin on 11 December noted that a new lava flow had traveled down the N flank. Crater incandescence continued to be observed at night.

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)