Sangay, located in Ecuador, has documented eruptions that date back to 1628 SE characterized by pyroclastic flows, lava flows, ash plumes, and lahars. The current eruption period began in March 2019 and has recently consisted of daily explosions, incandescent block avalanches, lava flows, and ash plumes (BGVN 48:03). This report describes similar activity of daily explosions, gas-and-ash emissions, light ashfall, crater incandescence, and incandescent material on the flanks, using information from Ecuador's Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), Servicio Nacional de Gestión de Riesgos y Emergencias (SNGRE), the Washington Volcanic Ash Advisory Center (VAAC), and various satellite data.

During March through August 2023, IG-EPN reported daily explosions, gas-and-steam and ash plumes that rose as high as 9 km above the crater, and frequent crater incandescence, often accompanied by incandescent avalanches of material and lava flows that descended the flanks of the volcano. The highest ash plume rose 9 km above the crater on 21 April and drifted W. Explosions occurred nearly every day, ranging from 5 to nearly 2,200 per day, the most of which occurred on 20 June 2023 (figure 150). The average number of daily explosions during the reporting period was 425, and the highest monthly average number of daily explosions was 755, which occurred during June 2023.

Figure 150. Graph showing the number of daily explosions at Sangay during March through August 2023. The number of explosions markedly increased during mid-June and remained higher during June through August compared to March through May. There were some data gaps during April and May due to technical problems in seismic data. Data courtesy of IG-EPN (March-August 2023 daily reports).

Table 13. Monthly summary of explosions and plume heights recorded at Sangay during March through August 2023. The average number of explosions do not account for days where the monitoring instruments were offline. Data courtesy of IG-EPN (March-August 2023 daily reports).

During March, activity consisted of 7-166 daily explosions and gas-and-ash emissions that rose as high as 2 km above the crater during 22 and 24 March and drifted N and NW. The Washington VAAC reported that gas-and-ash emissions rose 500-1,500 m above the crater and drifted in multiple directions. Nighttime crater incandescence was occasionally observed, accompanied by some incandescent material on the SE flank. On 1 March a lava flow was visible on the SE flank, accompanied by incandescent block avalanches. According to MOUNTS sulfur dioxide measurements taken throughout the month, emissions ranged between 44 and 2,049 tons per day (t/d). On 3 March a lava flow was observed on the SE flank 600 m below the crater rim. A lava flow was also visible on the SE flank on 13 and 22 March, accompanied by crater incandescence. A lahar was reported on 14 March. During 18-20 and 31 March incandescent block avalanches descended the S and SE flanks (figure 151).

Figure 151. Webcam image showing a lava flow, an incandescent block avalanche, and crater incandescence from Sangay at 2123 on 18 March 2023. Courtesy of IG-EPN Daily report.

Activity during April was characterized by 5-316 daily explosions, frequent nighttime crater incandescence, and gas-and-ash emissions that rose 1-9 km above the crater and drifted in multiple directions. The Washington VAAC reported that gas-and-ash emissions rose 500-7,900 m above the crater. According to MOUNTS sulfur dioxide measurements taken throughout the month, emissions ranged between 22and 1,725 t/d. During 5-6 April a lava flow descended the SE flank, reaching 1.8 km below the crater rim. During 12-18 crater incandescence was visible in the upper part of the flanks and incandescent material descended the SE flank as far as 1.5 km below the crater rim. On 17 April light ashfall was reported in Macas and on 18 April light ashfall occurred in Morona, Sucúa, Sinaí, and Logroño (figure 152). There were some reports of roaring sounds in Chonta Punta. Two large explosions were detected during 20-21 April that generated initial eruption columns that rose 8 km above the crater. During the night and early morning of 20-21 April GOES-16 satellite images showed a wide ash cloud that reached 9 km above the crater and drifted W, according to IG-EPN. Ashfall was reported in Chimborazo, Bolivar, Guayas, and Los Ríos. More ashfall was reported in Guamote and ash remobilization in Babahoyo on 22 April. A pyroclastic flow occurred at 0814 on 24 April that descended the SE flank. Ash emissions that same day rose 6 km above the crater and drifted NE and NW. The Washington VAAC reported that gas-and-ash emissions rose 7.9 km above the crater and drifted W and E. There were some technical problems with the seismic instrumentation, so seismic counts could not be included on 24-25 and 28-30 April. On 25 April the Washington VAAC reported four ash emissions; the first rose 1.2 km above the crater and drifted NE, the second rose 6 km above the crater and drifted SW, the third rose 3.3 km above the crater and drifted NW, and the fourth rose 1.5 km above the crater and drifted E. A GOES-16 satellite image taken at 1640 showed a gas-and-ash plume rising 6 km above the crater and drifted SW. Ashfall was reported in Ishbug Utucun. Ash emissions rose 1.5 km above the crater and drifted E, W, SW, and SW on 26 April and SNGRE reported light ashfall in Chimborazo and Guamote.

Figure 152. Photo of an ash plume rising as high as 4 km above Sangay’s crater at 0730 on 18 April 2023 and drifted ESE. Photo has been color corrected. Photo by Jorge Duchi, courtesy of IG-EPN.

There were 304-600 daily explosions detected during May, in addition to occasional crater incandescence and gas-and-ash emissions that rose 300-2,000 m above the crater and drifted in different directions, according to both IG and the Washington VAAC. MOUNTS sulfur dioxide measurements taken throughout the month ranged between 9.7and 1,912 t/d. Technical problems with the seismic instruments occurred during 1-22 May, so seismic and explosion counts could not be collected. Cloudy weather often obscured clear views of the summit, but intermittent crater incandescence was visible. Light ashfall was reported in Palmira and during the night in Chauzán, both in Chimborazo on 5 May. An incandescent lava flow was observed on the SE flank 500 m below the crater rim on 15 and 17 May. By 18 May the lava flow reached 1 km below the crater rim. Constant ash emissions on 20 May rose less than 2 km above the crater and ashfall was reported in Chimborazo and light ashfall was reported in Guamote and Alausí on 21 May. During 22-23 May a lava flow descended the SE flank 1 km below the crater rim, then 1.8 km below the crater rim, respectively. A pyroclastic flow occurred on 24 May and descended the SE flank at 0920. During the morning of 29 May several pyroclastic flows descended the SE flank, one of which occurred at 0610 (figure 153). Light ashfall was reported in Cebadas. Nighttime crater incandescence was visible and lava flows were reported on the S and SE flanks. On the morning of 30 May another pyroclastic flow was reported moving down the SE flank. Light ashfall was observed in Cebadas on 31 May. Additionally, nighttime crater incandescence and a lava flow on the SE flank were visible.

Figure 153. Webcam image of a pyroclastic flow descending the SE flank of Sangay at 0615 on 29 May 2023. Image has been color corrected. Courtesy of IG-EPN.

IG-EPN reported 158-2,190 daily explosions during June, frequent crater incandescence, and gas-and-ash emissions that rose 400-1,800 m above the crater and drifted in different directions, according to both IG and the Washington VAAC. Sulfur dioxide emissions of 30 to 797 t/d were recorded throughout the month and reported by MOUNTS. Incandescent avalanches were reported 1 km below the crater rim on 5 June, accompanied by crater incandescence. During 9-12 June an incandescent avalanche descended the SE flank and was accompanied by crater incandescence. A GOES-16 satellite image taken on 15 June showed an ash cloud that rose 1.8 km above the crater and drifted W; light ashfall was reported in Palmira. A pyroclastic flow traveled 500 m below the crater rim on the SE on 19 June. On 20 June gas-and-ash emissions rose 561 m above the crater and drifted SW and light ashfall was reported in Llagos.

During July, 148-1,200 daily explosions were recorded, frequent crater incandescence, and intermittent gas-and-ash emissions that rose 400-2,000 m above the crater and drifted in multiple directions, according to both IG and the Washington VAAC. MOUNTS data for sulfur dioxide emissions showed that measurements ranged 22-515 t/d. During 3-6 and 12-13 July incandescent material descended the SE flank 1-1.8 km below the crater rim. On 6 July explosions ejected incandescent material above the crater rim. During 9-10 July incandescent material was ejected up to 1 km above the crater rim.

Activity persisted during August, with 33-943 daily explosions, occasional crater incandescence, and gas-and-ash emissions that rose 300-2,800 m above the crater and drifted in different directions, according to both IG and the Washington VAAC. The amount of sulfur dioxide emitted during the month, according to MOUNTS was 27-641 t/d. During 4 and 6-13 August crater incandescence was accompanied by incandescent material descending the SE flank as far as 1.8 km below the crater rim; some material also was visible on the S flank on 11 August. Gas-and-ash emissions rose 500-2,200 m above the crater and drifted W and NW and ashfall was reported in Cebadas on 17 August. That same day, incandescent material was visible 1 km below the crater rim. On 19 August a GOES-16 satellite image showed a gas-and-ash emission rise 1.2 km above the crater and drifted NW; during the morning SGR reported light ashfall in Palmira and ROVE reported light ashfall in Cebadas. During 22-30 August crater incandescence was accompanied by incandescent material 1-1.8 km below the crater rim on the S and SE flanks. At 1500 on 25 August light ashfall was observed in Cebadas.

Satellite data. Thermal activity was consistently strong throughout the reporting period due to crater incandescence, block avalanches, and lava flows that primarily affected the S and SE flanks. This activity was detected by the MIROVA hotspots detection system (figure 154) and the MODVOLC Thermal Alerts system, which recorded a total of 137 hotspots. Infrared satellite imagery showed crater incandescence, incandescent block avalanches, and lava flows descending the SE flank (figure 155). Frequent sulfur dioxide plumes were captured by the TROPOMI instrument on the Sentinel-5P satellite, many of which exceeded 2 Dobson Units (DUs) and drifted in different directions (figure 156).

Figure 154. Strong thermal activity at Sangay occurred frequently during March through August 2023 due to crater incandescence and lava flows on the flanks; there was a gap in activity during late April through early May. Courtesy of MIROVA.

Figure 155. Strong thermal activity was visible in infrared (bands B12, B11, B4) satellite images showing crater incandescence and a lava flow (bright yellow-orange) descending the SE flank at Sangay on 17 March 2023 (top left), 20 June 2023 (top right), 25 July 2023 (bottom left), and 19 August 2023 (bottom right). Courtesy of Copernicus Browser.

Figure 156. Strong sulfur dioxide plumes from Sangay were frequently detected by the TROPOMI instrument on the Sentinel-5P satellite throughout the reporting period, as shown here on 2 March 2023 (top left), 9 April 2023 (top right), 21 May 2023 (bottom left), and 15 July 2023 (bottom right). Each of the plumes shown here exceed 2 Dobson Units (DUs) and drifted W, E, SW, and W, respectively. Sangay is located toward the bottom of the satellite images; Colombia’s Nevado del Ruiz is the topmost symbol that also frequently emits sulfur dioxide plumes. Courtesy of NASA Global Sulfur Dioxide Monitoring Page.

Geological Summary. The isolated Sangay volcano, located east of the Andean crest, is the southernmost of Ecuador's volcanoes and its most active. The steep-sided, glacier-covered, dominantly andesitic volcano grew within the open calderas of two previous edifices which were destroyed by collapse to the east, producing large debris avalanches that reached the Amazonian lowlands. The modern edifice dates back to at least 14,000 years ago. It towers above the tropical jungle on the east side; on the other sides flat plains of ash have been eroded by heavy rains into steep-walled canyons up to 600 m deep. The earliest report of an eruption was in 1628. Almost continuous eruptions were reported from 1728 until 1916, and again from 1934 to the present. The almost constant activity has caused frequent changes to the morphology of the summit crater complex.

Information Contacts: Instituto Geofísico, Escuela Politécnica Nacional (IG-EPN), Casilla 17-01-2759, Quito, Ecuador (URL: http://www.igepn.edu.ec/); Servicio Nacional de Gestion de Riesgos y Emergencias (SNGRE), Samborondón, Ecuador (URL: https://www.gestionderiesgos.gob.ec/); Washington Volcanic Ash Advisory Center (VAAC), Satellite Analysis Branch (SAB), NOAA/NESDIS OSPO, NOAA Science Center Room 401, 5200 Auth Rd, Camp Springs, MD 20746, USA (URL: www.ospo.noaa.gov/Products/atmosphere/vaac, archive at: http://www.ssd.noaa.gov/VAAC/archive.html); 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/); NASA Global Sulfur Dioxide Monitoring Page, Atmospheric Chemistry and Dynamics Laboratory, NASA Goddard Space Flight Center (NASA/GSFC), 8800 Greenbelt Road, Goddard MD 20771, USA (URL: https://so2.gsfc.nasa.gov/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/); MOUNTS Project (Monitoring Unrest From Space), an operational monitoring system for volcanoes using Sentinel satellite data from ESA's Copernicus, Open Access Hub, hosted at UNAM and CT TU-Berlin (URL: http://www.mounts-project.com/home).