Activity during late March 2006 through November 2007 at Santa Maria's Santiaguito lava-dome complex included ash emissions similar to those during October 2005-March 2006 (BGVN 31:04). The Instituto Nacional de Sismologia, Vulcanologia, Meterologia, e Hidrologia (INSIVUMEH), the Coordinadora Nacional para la Reducción de Desastres (CONRED), and the Washington Volcanic Ash Advisory Center (Washington VAAC) provided information for this report.

A large number of weak-to-moderate explosions continued at Santiaguito, producing ash plumes that rose above the volcano and depositing ash through the surrounding area. On numerous occasions, short pyroclastic flows and block-and-ash avalanches descended the S and SW flank of Caliente Dome. Several lahars were recorded from June to October 2007 along the Nima I and Samala rivers.

Activity during March-December 2006. A large number of weak-to-moderate explosions occurred during 22-28 March 2006, producing ash plumes that rose to ~ 1 km above the volcano. The plumes drifted SW, depositing ash 8-10 km away. On several days, short pyroclastic flows and block-and-ash avalanches descended the SW flank of Caliente Dome. Explosions on 17 April produced ash plumes 500-900 m high, and pyroclastic avalanches sent material down the S flank.

About two months passed from mid-April until mid-June without reported explosive activity. Then, explosions on 15-16, 18, 21, and 26 June produced gas-and-steam plumes with moderate to no ash content that reached 1 km above the summit. Lahars were observed on 18 and 19 June.

On 1 July small ash plumes noted by the Washington VAAC reached altitudes of 5.8 km and drifted SW. INSIVUMEH reported that another ash plume on 3 July rose 800 m. Steaming from an incandescent avalanche deposit was also visible from the NE base of Caliente cone. Explosions on 9 and 10 August produced gas-and-steam plumes with little-to-no ash content that reached heights of ~ 1.5 km and drifted SW. Two explosions on 21 September caused minor ashfall and small block avalanches. A pyroclastic flow the next day was generated by material coming off of Caliente Dome. Additional explosions on 26 and 29 September again caused ashfall to the SW. Lava extrusion on the 29th triggered avalanches that sent blocks to the base of the crater.

According to the Washington VAAC, minor emissions on 18, 26, 27, and 30 October were visible on satellite imagery. The small plumes of gas and light ash drifted W. Minor emissions seen on satellite imagery on 14 November sent small ash clouds WSW. Explosion plumes reached an altitude of 5.3 km on 15 November, causing ashfall to the N. Lava flows that day moved down the SW, S, and SE flanks of Caliente Dome. On 17 November, explosions produced white-and-gray plumes that drifted SW, where light ashfall was reported. Based on satellite imagery, the Washington VAAC reported more gas-and-ash emissions on 19 November; plumes drifted W.

Satellite imagery revealed ash plumes on 5, 7, and 10 December that drifted SW, NW, and W, respectively. Constant incandescent avalanches on 8 December came from the S and SE edge of dome and from the toe of the active lava flow on the SW flank. Ash plumes caused slight ashfall to the SW. On 28 December a series of small sector collapses from the SW edge of the Caliente Dome produced pyroclastic flows that traveled about 2 km down a ravine. Another collapse produced pyroclastic flows and incandescent blocks on 29 December. Thick ash plumes associated with the pyroclastic flows on both days reached an altitude of 4.3 km and drifted W and NW.

Activity during January-March 2007. Minor emissions of gas and possible ash visible in satellite imagery on 1 and 2 January with narrow plumes drifting WSW were reported by the Washington VAAC. On 4 January there were 37 weak to moderate explosions; the moderate events caused ashfall S and SE in the ranching areas of Monte Bello and Monte Claro. About 21 block-and-ash flows were also observed. Explosions on 5 January produced ash clouds that rose to 4.3-4.8 km, with ashfall noted to the S and SE. Ash puffs were visible on satellite imagery during 7-8 January. Explosions on 12 January sent ash plumes to altitudes of 3.9-4.2 km. Plumes drifted SW and ashfall was reported downwind. Incandescent blocks rolled SW on 12 and 16 January. Based on satellite imagery, diffuse ash plumes identified on 10, 12, and 14-16 January drifted SW and W.

Explosions on 17, 19, and 23 January sent ash plumes to altitudes of 4.1-4.7 km that drifted SW. Incandescent blocks continuously rolled down the S and SW flanks. Based on satellite imagery, the Washington VAAC reported diffuse ash plumes on 18, 24, and 30 January. Explosions produced minor ashfall on 25, 26, and 29 January. Block-and-ash avalanches descended the SW flank of Caliente Dome on 25 and 29 January. Another ash plume on 31 January rose to 4.8 km and drifted SW.

Explosions on 5 February produced ash plumes that rose to altitudes of 4.8 km. On 5 February, plumes drifted SW and S causing ashfall downwind. Block-and-ash avalanches descended the SW and S flanks of Caliente Dome. Fumarolic plumes drifted SW. Based on satellite imagery, the Washington VAAC reported that ash plumes drifted W on 2 February, and that diffuse plumes drifted SW and S in a fan shape on 8 February. A thermal hotspot was also detected on 8 February imagery. Avalanches descended the SW flank to the base of Caliente Dome and explosions produced diffuse ash plumes on 15 February. Explosions on 19 February again produced plumes and ashfall to areas SW.

Diffuse ash plumes seen in satellite imagery drifted mainly W and N during 22, 23, and 25-27 February. Seven explosions on the 26th produced ash plumes that rose to altitudes of 4.4-4.6 km and drifted SW. Avalanches occurred from lava-flow fronts on the SW flanks and from the S edge of Caliente Dome. A hotspot was seen on satellite imagery. On 27 February, explosions occurring at an approximate rate of three per hour produced ash plumes that reached altitudes of 4.8 km. Occasionally explosions were accompanied by pyroclastic flows that traveled SW.

A SW-directed diffuse ash plume on 5 March was followed the next day by another diffuse plume and a hotspot seen on satellite imagery. Explosions produced ash-and-steam plumes that rose to altitudes of 3.8-4.8 km during 21-22 and 25 March and drifted W; ash fell nearby. On 25 and 26 March, avalanches occurred from lava-flow fronts on the SW flanks of Caliente Dome. A 27 March explosion produced a pyroclastic flow that traveled down the SW flank. Explosions produced ash plumes that rose to an altitude of 5 km on 29 March; ashfall was reported near the Observatory Vulcanológico de Santiaguito (OVSAN), about 5 km S. On 30 March diffuse ash plumes were again visible on satellite imagery drifting SW.

Activity during April-June 2007. On 2 April, INSIVUMEH reported that ash plumes rose to 4.4 km and drifted SW. Explosions occasionally produced ash plumes that rose to altitudes of 5.3 km and drifted E on 11 and 16 April. Lava-flow fronts on the SW flanks of Caliente Dome emitted gases on 11 April and produced avalanches of block and ash on 16 April. On 13 April, the Washington VAAC reported that an ash plume was visible on satellite imagery drifting W. Explosions on 20 and 23 April produced ash plumes that rose to altitudes of 5.3 km and caused ashfall up to 9 km SW. On 23 April, lava flows on the SW and NE flanks of Caliente Dome produced small landslides composed of blocks. Diffuse ash plumes were seen in satellite imagery on 18, 23, and 24 April, and gas plumes possibly containing ash on 20 April. Explosions on 26 April produced ash plumes that rose to altitudes of 4.4-4.8 km and drifted SW. More ash plumes and steam-and-ash plumes drifted S and WSW on 26 and 28 April, respectively. On 30 April, explosions caused ashfall to the SW; lava extrusion was low.

Based on satellite imagery, the Washington VAAC reported that ash plumes drifted S on 9 May. INSIVUMEH reported on 10 May that rain caused landslides S down the Nimá I river, near the Observatory about 5 km S of the lava dome. Explosions from Caliente Dome during 10-11 and 14 May produced gas-and-ash plumes that rose to altitudes of 4.4-5.3 km and drifted SW and E. Ashfall was reported from areas S and SW on 10 May. Avalanches of blocks and ash from the SW edge of Caliente Dome were observed on 14 May.

OVSAN and several seismic stations registered a lahar on 5 June. The lahar descended the Nimá I river and carried blocks 1-1.5 m in diameter and tree branches. The approximately 12-m-wide by 3-m-thick deposit was hot and smelled of sulfur. On 7 June, INSIVUMEH reported explosions of steam and ash that rose to altitudes of 4.3-4.7 km and drifted SW. A plume rose from a cooling lava flow at the NE base of the lava dome. Continuous landslides of blocks and ash were noted on the SW flank.

Activity during July-October 2007. During 11-12 July there were 27 seismically-detected explosions. Additional explosions on 13 July produced ash plumes that rose to altitudes of 4.3-5.3 km. Ash plumes from the explosions drifted SW and caused ashfall. Incandescent avalanches of blocks from Caliente Dome were observed.

On 31 August 2007, INSIVUMEH reported that a lahar, 8 m wide and 1.5 m high, descended S down the Nima I river, carrying fine material, tree branches, and blocks. On 25 September 2007 a lahar about 18 m wide descended S down Santa María's Nima I river. On 12 October 2007, lahars in multiple drainages that carried tree branches, fine sediment, and blocks of multiple sizes, flooded the Samala river (to the E and S) as far as the Pacific coast, 70 km S.

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, Vulcanología, Meteorología, 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/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS E/SP23, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: http://www.ospo.noaa.gov/Products/atmosphere/vaac/); Coordinadora Nacional para la Reducción de Desastres (CONRED), Av. Hincapié; 21-72, Zona 13, Guatemala City, Guatemala (URL: http://www.conred.org/).