This summary of activity at Santa María's Santiaguito lava-dome complex, taken largely from Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hidrologia (INSIVUMEH) reported for October 2005 to January 2006. During this interval Santa María continued to emit occasional ash plumes.

During 26-31 October 2005, several explosions took place and plumes rose to a maximum of ~ 5 km altitude on 28 October. In early November, several explosions occurred producing ash plumes to an altitude of ~ 5 km. A few weak avalanches of volcanic material were observed SW of the lava dome.

Explosions produced several ash plumes to ~ 5 km altitude during 11-14 November 2005. Several small pyroclastic flows traveled down the SW, NE, and S flanks of Caliente dome. Frequent avalanches of volcanic material occurred off of the fronts of active lava flows mostly to the W of Caliente dome, and less frequently to the S and NE. An ash-and-gas emission on 14 November produced a cloud that was visible on satellite imagery.

During 17-21 November, Santa María produced weak-to-moderate explosions, sending ash plumes to an altitude of ~ 4.6 km. Several small pyroclastic flows traveled down the SW and NE flanks of Caliente dome, stopping at the base of the dome. Avalanches spalled off of the fronts of active lava flows and traveled SW.

On 24 November at 0955, an eruption produced an ash cloud to an altitude of ~ 4 km accompanied by a pyroclastic flow to the S. Fine ash fell 6-7 km S of the volcano, impacting properties in the area.

Moderate-to-strong explosions in December produced ash plumes that rose ~ 1.5-2.5 km. Pyroclastic flows occasionally accompanied explosions and traveled towards the SW. Several avalanches of volcanic material also occurred during the report period.

Throughout January 2006, explosions continued to occur sending resultant ash emissions to the SW. Lava avalanches originated from the SW edge of the Caliente dome and from the fronts of active lava flows on the SW flank. An explosion on the morning of 11 January 2006 generated a small pyroclastic flow that traveled down Caliente dome to the NE. INSIVUMEH reported on 16 January that a slight decrease in explosive activity was observed during the previous month. On 16 January there were reports of a small amount of ashfall 25 km SW in the urban area of San Felipe Retalhuleu.

During 1-3 February, weak-to-moderate explosions took place at Santiaguito's lava-dome complex, producing plumes that rose to a maximum height of 1 km above the volcano. On 1 February at 0657 and 0708, moderate explosions were accompanied by pyroclastic flows. Lava extrusion at Caliente dome produced block-and-ash flows that descended the dome's S, E, and W sides. Several explosions on 9 February also produced small pyroclastic flows that traveled down the SW and SE sides of Caliente dome. On 15-17 February, pyroclastic flows traveled SW and NE, associated with avalanches of incandescent volcanic material spalled off of active lava-flow fronts.

On 4, 6, and 7 March, satellite imagery showed small ash plumes emitted from the lava-dome complex. The plumes reached ~ 3 km above the volcano. On 6 March around 0733, a moderate explosion produced an ash plume and pyroclastic flows. A strong explosion later that day, at 1025, sent an ash plume ~ 3 km above the volcano that deposited ash throughout the volcanic complex. The explosion was accompanied by pyroclastic flows down the NE and SW flanks. Fine ash drifted S falling on properties in that area. On 12 March, there were avalanches of volcanic blocks and ash. On 13 March, a pyroclastic flow traveled down the S flank of Caliente dome.

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.

Information Contacts: Instituto Nacional de Sismologia, Vulcanologia, Meteorologia e Hidrologia (INSIVUMEH), Unit of Volcanology, Geologic Department of Investigation and Services, 7a Av. 14-57, Zona 13, Guatemala City, Guatemala (URL: http://www.insivumeh.gob.gt/).