The Instituto Nacional de Sismología, Vulcanología, Meteorología e Hidrología (INSIVUMEH) reported high levels of ongoing eruptive activity at Santa Maria’s Santiaguito dome complex during 16-23 September, with continuing lava extrusion at Caliente dome. Daily explosions, 2-6 per hour when reported, generated gas-and-ash plumes that rose 700-1,000 m above the dome and drifted in multiple directions. Effusion of blocky lava and collapses of previous deposits produced block avalanches that descended mainly the W and SW flanks; the collapsed material produced short pyroclastic density currents during 22-23 September. Incandescence during dark hours was visible from Caliente dome and block avalanches. Special reports issued at 1305 on 16 September and at 1337 on 20 September noted that heavy rainfall generated hot lahars in the Cabello de Ángel drainage (SE). The lahars were a mixture of water and sediments, along with tree trunks, branches, and blocks up to 3 m in diameter, and a sulfur odor. Hot lahars moving down the Tambor drainage (SSW) were noted in special reports issued at 1317 on 16 September, at 1345 on 18 September, and at 1346 on 20 September. These lahars were also a mixture of water and sediments, with tree trunks, branches, and blocks up to 1 m in diameter, and 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)