INSIVUMEH reported that during 4-10 August daily explosions at Santa María’s Santiaguito lava-dome complex generated ash plumes that rose as high as 1 km above the summit and drifted as far as 7 km SW and W. Incandescence from the complex was occasionally visible at night. Collapses of blocky lava from Caliente dome sent avalanches down the S, SW, and W flanks, often reaching the base, and caused minor ashfall mostly on the volcano’s flank. Ashfall was also reported in San Marcos (8 km SW), Loma Linda Palajunoj (6 km WSW), and surrounding farms during 3-4 and 8-9 August. Heavy rainfall on 7 August caused a lahar to descend the Tambor River, carrying branches, tree trunks, and blocks up to 3 m in diameter.

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)