CONRED stated that at 0808 on 18 August a strong and loud explosion at Santa María's Santiaguito lava-dome complex generated a dense ash plume that rose 1.5 km and drifted S and SW. Pyroclastic flows descended the flanks. INSIVUMEH reported that gas emissions were observed during 20-21 August, along with some weak avalanches originating at the dome. Another strong and loud explosion was detected at 0203 on 23 August, generating a mushroom-shaped ash plume that rose 2.5 km and drifted W and SW. Pyroclastic flows descended the E flank. Ashfall was reported in San Marcos (10 km SW), Loma Linda (6 km WSW), and Palajunoj (18 km SSW), and possibly in the local ranches of El Faro and La Florida. Later that day three moderate explosions produced ash plumes that rose 800 m and drifted W and SW, causing ashfall in San Marcos, Loma Linda, and Palajunoj.

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.

Sources: Coordinadora Nacional para la Reducción de Desastres (CONRED), Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH)