Based on analyses of satellite imagery, the Washington VAAC reported that during 5-6 May ash plumes from Santa María's Santiaguito lava dome complex rose to an altitude of 4 km (13,000 ft) a.s.l. and dissipated within about 75 km SW. On 6 May ash plumes also rose to an altitude of 6.7 km (22,000 ft) a.s.l. and dissipated within 10 km NW. Plumes also drifted S and SE. During 5-6 May INSIVUMEH reported that an explosion produced an ash plume that rose 800 m above Caliente cone and drifted W. Ash fell at beach areas and weak avalanches occurred with a lava flow on the E flank. Two areas of incandescence were observed on the S flank of the lava dome. During 8-9 May steam plumes rose 100 m above the Caliente cone crater and a few avalanches descended the SE flank. Explosions during 9-10 May produced ash plumes that rose 1.2 km above the crater and pyroclastic flows from the SW edge of the crater that were deposited in the Río Nima I and Río Nima II drainages. Ash plumes drifted W and block avalanches descended the E, S, and W flanks.

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)