INSIVUMEH reported that the eruption at Santa María’s Santiaguito lava-dome complex continued during 1-7 December. Avalanches generated by both lava effusion at the WSW part of Caliente dome and collapsing material descended the flanks in multiple directions, often reaching the base of the dome. Periodically the avalanches produced curtains of ash along their paths that dissipated near the volcano. Some of the avalanches were preceded by explosions detected by the seismic network and some were audible several kilometers away. During 2-3 and 6-7 December ash plumes rose 500 m above the summit and drifted 10 km NW and W, causing ashfall in areas downwind including San Marcos Palajunoj (8 km SW) and Loma Linda (6 km WSW). During 3-4 December ash-and-steam plumes rose 900 m and drifted SW and W.

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)