In a special report posted on 25 May, INSIVUMEH reported energetic explosive activity at Caliente cone, part of Santa María's Santiaguito lava-dome complex. Loud explosions at 0804 and 0918 generated mushroom-shaped ash clouds that rose as high as 2.5 km and drifted more than 40 km WSW. Pyroclastic flows traveled 2 km E, S, and W, in the San Isidro and Cabello de Ángel drainages. Ashfall was reported in areas downwind including El Nuevo Palmar (12 km SSW), San Felipe (15 km SSW), and Retalhuleu (27 km SW), the villages of Las Marias, Loma Linda, and San Marcos (10 km SW), Palajunoj (18 km SSW), and the El Faro (SW flank), La Florida (5 km S), Patzulin (SW flank), and El Patrocinio ranches. During 28-29 May white-and-gray plumes rose 400 m above the cone and drifted SW.

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)