The Santiaguito lava-dome complex of Guatemala's Santa María volcano has been actively erupting since 1922. The lava dome-complex formed within a large crater on the SW flank of Santa Maria that formed during the 1902 eruption. Ash explosions, pyroclastic flows, and lava flows have emerged from Caliente, the youngest of the four vents in the complex, for more than 40 years. The Caliente vent has an elevation of about 2.5 km, and the summit of Santa Maria is at about 3.7 km elevation. A lava dome that appeared within the summit crater of Caliente in October 2016 has continued to grow, producing frequent block avalanches down the flanks. Recent activity, including ash plumes, block avalanches, and lava flows (BGVN 47:08) has continued during August through November 2022, using information from Guatemala's INSIVUMEH (Instituto Nacional de Sismologia, Vulcanologia, Meterologia e Hidrologia) and satellite data.

Activity during August consisted of white gas-and-steam emissions that rose 200-800 m above the crater and drifted 3-12 km SW, W, S, SE, and NW. Active flows were detected on the W, SW, SE, WSW, and S flanks throughout the month. Nighttime and early morning incandescence was recorded in the crater of the Caliente dome, and weak-to-moderate block-and-ash avalanches on the W, SW, WSW, S, and SE flanks and at the front and middle of active lava flows; fine ash particles remained suspended in the area due to the avalanches. Ash plumes resulting from the block-and-ash avalanches rose 50 m-1.5 km above the crater and drifted E and W. On 3 August fine ashfall and a faint smell of sulfur was reported 15 km S of the volcano. Collapses were observed in the front of the active lava flow in the San Isidro (SSW) and El Tambor drainages on 4 August. These collapses generated loud sounds resulting from rock falls and raised ash columns up to 1 km high that produced ashfall in the surrounding area on 4-5, 8, 20, and 26 August, including La Florida (6 km S), Monte Claro, San Marcos Palajunoj (8 km SW), and Loma Linda (7 km W). By 6 August the lava flow in the San Isidro drainage measured approximately 3.7 km long. As it continued to move, avalanches with moderate pyroclastic flows were generated, burning some vegetation, and distributing ash plumes to the SW. Fine ash particles and the smell of sulfur were reported in Las Marías on 6 August. INSIVUMEH reported that on 12 August the lava flow on the SW flank of the Caliente dome measured 4 km long. During 17-18 and 25 August strong rainfall generated lahars in the Cabello de Ángel drainage toward the SSE, E, and SW flanks of the volcano. Lahars carried rocks up to 1 m in diameter and tree trunks and branches. Collapses from the middle part of the lava flow in the San Isidro and El Tambor drainages generated ash columns that rose 100-500 m above the surface on 20 August. A faint sulfur smell was also reported up to 10 km S of the volcano. On 24 August ashfall was reported in San Marcos Palajunoj. The active lava flow on the SW flank that moved to the W and SW was 4.2 km long on 30 August 2022.

Similar activity continued during September, with gas-and-steam emissions rising 200-800 m above the Caliente dome and drifting as far as 10 km in different directions. Dome incandescence and block-and-ash avalanches descending the W, SW, and S flanks were reported. Occasional explosions caused incandescent material to descend all sides of the Caliente dome. Some block collapses at the front and middle of the active lava flow in the San Isidro and El Tambor drainages and on the S, SE, WSW, and E flanks generated ash clouds that rose 500-600 m above the surface and drifted up to 7 km W and SW. On 5 September the lava flow from the SW flank remained 4.2 km long. On 8, 9, 13, 19, and 27 September strong rainfall generated lahars in the Cabello de Ángel drainage toward the SSW and SSE, carrying tree trunks, branches, and blocks up to 1 m in diameter. Fine ash was uplifted from avalanches on 15 September and distributed SW, causing ashfall in Monte Claro. Seismic stations recorded some weak explosions that produced gas-and-steam plumes during 27-28 September.

During October, gas-and-steam emissions rose 300-1,000 m above the Caliente dome that drifted as far as 7 km and in different directions. Incandescence was visible in the dome and avalanches descended the W, S, and SW flanks. Block collapses continued at the front of the active lava flow in the San Isidro, El Tambor, and Zanjón Seco drainages and the WSW and S flanks, which generated ash plumes that rose several hundred meters above the surface. Seismic stations recorded weak explosions that produced gas-and-steam emissions on 4, 10, 15, and 27 October. On 7 October the smell of sulfur was reported to the W and SW of the volcano. Weak explosions on 7 October ejected incandescent material that fell on all flanks of the dome. On 12, 13, 21, and 30 October weak avalanches produced fine ash particles that fell around the perimeter of the volcano. On 17 October the lava flow on the SW flank remained 4.2 km long. During 27-29 and 31 October ash was generated from avalanches of material that drifted to the SE and S.

Gas-and-steam emissions during November rose 200-700 m above the crater and drifted as far as 6 km in multiple directions. Constant crater incandescence was observed, and active lava flows traveled WSW, W, SW, and S. Weak-to-moderate avalanches occurred in the front and middle of the lava flow on the W, SW, and S flanks, sometimes causing fine ash particles to fall on the volcanic perimeter. Seismic stations recorded periods of degassing and occasional explosions that generated gas-and-steam plumes on 3 and 8 November; on 23 November a gas-and-steam and ash plume rose 700 m above the crater. Due to heavy rainfall, lahars were reported in the Cabello del Ángel drainage on 3 and 7 November moving to the SSW, carrying tree trunks and branches and blocks up to 1 m in diameter. On 5 November weak-to-moderate explosions generated fine ashfall in Finca San José and La Quina. Block collapses from the lava flow in the San Isidro, El Tambor, and Zanjón Seco drainages produced ash clouds that rose to several hundred meters above the surface on 6, 14, 15, 18, and 29 November. On 6 November the effusion rate and advancement of the lava flow markedly decreased in the El Tambor and San Isidro drainages. INSIVUMEH reported that on 16 November the active lava flow stopped advancing. On 22 November explosions were detected in the summit crater, accompanied by nighttime crater incandescence and constant avalanches on the W and SE flanks. Explosions on 24 November generated a gray ash plume that rose 700 m above the crater and drifted SW.

The MIROVA (Middle InfraRed Observation of Volcanic Activity) graph showed low-to-moderate thermal anomalies during the reporting period (figure 134). There were two short gaps in activity during early September and late September through early October. A total of 13 MODVOLC thermal alerts were issued: four during August, one during September, four during October, and four during November. Due to bad weather, clear views of the summit were obscured in infrared satellite imagery.

Figure 134. Low-to-moderate thermal anomalies were often detected at Santa María during August through November 2022, as shown on this MIROVA graph (Log Radiative Power). Anomalies varied in intensity, and two short gaps in activity were noted during early September and late September through early October. Courtesy of MIROVA.

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 Hydrologia (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/); MIROVA (Middle InfraRed Observation of Volcanic Activity), a collaborative project between the Universities of Turin and Florence (Italy) supported by the Centre for Volcanic Risk of the Italian Civil Protection Department (URL: http://www.mirovaweb.it/); Hawai'i Institute of Geophysics and Planetology (HIGP) - MODVOLC Thermal Alerts System, School of Ocean and Earth Science and Technology (SOEST), Univ. of Hawai'i, 2525 Correa Road, Honolulu, HI 96822, USA (URL: http://modis.higp.hawaii.edu/).