CONRED and INSIVUMEH reported that activity at the Santa María's Santiaguito lava-dome complex increased on 9 May. Pyroclastic flows descended the E and SE flanks, and a dense ash plume rose to an altitude of 7.6 km (25,000 ft) a.s.l. Ashfall was reported in areas at least 20 km away, including Las Marías, San Marcos (10 km SW), Palajunoj (18 km SSW), El Faro (SW flank), La Florida (5 km S), Patzulín, and Quetzaltenango (18 km WNW); about 130 people were evacuated from these areas due to persistent airborne ash. A deep notch left in the crater between the E and NE flanks channeled a pyroclastic flow which traveled 7 km into the Nima I drainage (S flank). Deposits in the drainage were estimated to be a million cubic meters; secondary explosions in the drainage were caused by the interaction of water and these hot deposits.

INSIVUMEH noted that activity returned to a normal range on 10 May, with 2-3 explosions per hour generating ash plumes that rose 800 m and drifted W. On 11 May explosions produced ash plumes that rose 800 m, drifted SW, and caused ashfall in San Marcos and the El Rosario Palajunoj finca.

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)