In a special bulletin posted on 29 January, INSIVUMEH reiterated that the eruption at Santa María’s Santiaguito lava-dome complex is in a high-extrusion phase. The lava dome in the crater continued to grow and produce avalanches, and two lava flows were active on the W and SW flanks. Seismic data indicated an intensification of descending avalanches starting around 1845 that likely affected the S and SW flanks, though cloudy weather prevented visual confirmation. Notable ashfall was reported in San Marcos Palajunoj (8 km SW), El Palmar (12 km SSW), Quetzaltenango (18 km WNW), and especially in Loma Linda (6 km WSW). Avalanches continued to be detected by the network and seen by OVSAN (Observatorio del volcán Santiaguito) observers through 31 January. The avalanches originated from collapses of the lava flow on the SW flank and descended the W and SW flanks. During 30 January until about 1800 on 31 January a total of 10 pyroclastic flows were detected by the seismic network and observed in webcam images. During 31 January-1 February dense gas emissions rose 600-800 m above the dome, and nighttime incandescence emanated from the dome and the W-flank flow. Avalanches continued to descend the SW and W flanks, several reached the base of the cone.

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)