INSIVUMEH reported that at 1405 on 5 September a lahar descended Santa María's Nima I drainage on the S flank carrying mostly fine sediment and 50-cm-diameter blocks, but also a small percentage of blocks 1-2 m in diameter. During 5-10 September white plumes rose 200-500 m and drifted W, SW, E, and NE. A few weak avalanches descended the S part of the active crater of the Santiaguito lava-dome complex. On 10 September another lahar traveled down the Nima I drainage, carrying blocks up to 3 m in diameter. The lahar was 15 m wide, 6 m deep, and had a sulfur odor.

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)