During 19-20 May, INSIVUMEH reported that hot lahars traveled down Santa María's Nima I, Nima II, and San Isidro rivers. The lahar in the San Isidro channel was 30 m wide and 1.5-2 m deep, emitted a sulfur odor, and carried blocks up to 2 m in diameter. Explosions from the Santiaguito lava dome complex produced ash plumes that rose to an altitude of 2.9-3.4 km (9,500-11,200 ft) a.s.l. and drifted SW. The next day, an explosion produced a plume that rose to an altitude of 3.3 km (10,800 ft) a.s.l. and drifted E and a pyroclastic flow that traveled SW. On 21 May another lahar descended the Nima II River.

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)