Based on analyses of satellite imagery and reports from INSIVUMEH, the Washington VAAC reported that on 23 March diffuse gas-and-ash plumes from Santa María's Santiaguito lava-dome complex drifted 33 km SW. Ashfall was noted in areas within 18 km of the volcano. On 24 March an ash plume drifted 26 km SW. The next day rockfalls occurred around the summit area and gas-and-ash plumes drifted 28 km SE, S, and SW. A thermal anomaly was detected in satellite imagery at night.

INSIVUMEH reported that during 25-27 March explosions generated ash plumes that rose 800-900 m above the crater and drifted in multiple directions. Lava flows continued to produce avalanches that descended the flanks. Ashfall was reported 5 km S at Observatory Vulcanológico de Santiaguito (OVSAN), at the El Faro, La Florida, and Patzulin ranches (SW), and in the village of Santa María de Jesús (SE). On 26 March an explosion was followed by a pyroclastic flow that traveled down the W flank of Caliente Cone.

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: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH), Washington Volcanic Ash Advisory Center (VAAC)