INSIVUMEH reported that heavy rain at Santa María on 20 September produced hot lahars in the San Isidro-Tambor River (S), a tributary of Salamá River. The lahars were 25 m wide, 2 m deep, had a sulfur odor, and carried branches, tree trunks, and blocks up to 2 m in diameter. Lahars also descended the Nimá I (S) drainage. On 21 September explosions generated ash plumes that rose 800 m above the crater rim and drifted W and SW; minor amounts of ash fell locally. Lahars descended the Nimá I, Salamá, and San Isidro drainages. During 24-25 September explosions produced ash plumes that rose 500-700 m and drifted SW. Avalanches of material traveled down the SE and NE 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.

Source: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia, e Hidrologia (INSIVUMEH)