Ethiopia's Erta Ale basaltic shield volcano has had at least one active lava lake since the mid-1960s, and possibly much earlier. Two active craters (north and south pits) within the larger oval-shaped summit caldera have exhibited periodic lava fountaining and lava lake overflows for many years. During January 2017-March 2020 a vent at the southeast caldera, a few kilometers SE of the summit caldera, produced lava flows that extended many kilometers from the main vents. Since March 2020 pulses of activity from both pit craters in the summit caldera have been recorded in numerous satellite thermal images. This report covers activity from September 2021-April 2022 when both the north and south pits were intermittently active. Information comes primarily from satellite imagery and thermal data, although reports and photographs from ground-based expeditions that periodically visit the site are occasionally available.

Multiple breakouts from persistent lava flows originating at the southeast caldera tapered off in March 2020; after this, intermittent low levels of thermal activity were focused at the N and S pit craters of the summit caldera, with occasional pulses of stronger activity in late November 2020 at the S pit crater and in late March and late May 2021 at the N pit crater (BGVN 46:02, 46:10). A return to more vigorous thermal activity in September 2021 was indicated by MODIS satellite data as an increased number of MODVOLC thermal alerts, increases in the MIROVA log radiative power frequency and intensity (figure 107), and numerous Sentinel-2 satellite images of thermal anomalies. Visitors to the site in December 2021, and January and February 2022, confirmed the active lava lake at the S pit crater.

Figure 107. The Log Radiative Power for thermal activity at Erta Ale increased during September 2021 and remained elevated through April 2022, as seen in the MIROVA graph of activity from 6 June 2021 through April 2022 (top). The MIROVA distance graph (bottom) confirms that all of the activity was located at the N and S pit craters, compared with the earlier flow activity located many kilometers from the summit and southeast calderas (figure 97, BGVN 45:05). Courtesy of MIROVA.

Only a few of the Sentinel-2 satellite images of Erta Ale are cloudy, providing a consistent record of the changes in thermal activity in the summit caldera during the period. The S pit crater had thermal anomalies of varying intensity throughout, but the N pit crater was more intermittent. A very weak anomaly appeared at the N pit on 31 August 2021, but then not again until 10 October. It was larger on 15 October and bright on 30 October. At the S pit, the anomaly was present in all September and October images, and brightest on 20 September. Double anomalies appeared at the S pit for most of October (figure 108). MODVOLC thermal alerts were recorded on four days in September and nine days of October.

Figure 108. A very weak anomaly appeared at the N pit of Erta Ale on 31 August 2021 (top left), but then not again until 10 October. It was larger on 15 October (bottom 2nd from left) and very bright on 30 October (bottom right). At the S pit, the anomaly was present in all September and October images, and brightest on 20 September (top, 2nd from right). Double anomalies appeared at the S pit for most of October (bottom). Sentinel-2 images use Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

The thermal anomaly was weak at the N pit on 4 November 2021, brighter on 19 November, brightest on 24 November, and very weak or absent on 29 November. It was very bright on 14 December, but absent the other days of December. At the S pit, two anomalies were present in most images, one much brighter than the other, with a similar size and intensity throughout (figure 109). MODVOLC thermal alerts were issued on eleven days during November and six days during December.

Figure 109. The thermal anomaly was weak at the N pit of Erta Ale on 4 November 2021 (top left), brighter on 19 November (top, 2nd from left), brightest on 24 November (top, 2nd from right) and very weak or absent on 29 November (right). It was very bright on 14 December (bottom 2nd from left), but absent the other days of December. At the S pit, two anomalies were present in most images from November and December, one much brighter than the other, with a similar size and intensity throughout the period. Sentinel-2 images use Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

No thermal anomaly was present at the N pit for all of January or February 2022. At the S pit, a single weak anomaly was present during January, and a brighter single or double anomaly was present throughout February and early March (figure 110). A single MODVOLC thermal alert was issued on 24 January, and alerts were reported on four days during February. A weak thermal anomaly was present at the N pit in the 29 March 2022 image and persisted in all of the April images. Consistent size and intensity double anomalies, one bright and one dim, were present at the S pit in all images for March and April (figure 111). MODVOLC thermal alerts were issued for five days during March and six days during April 2022.

Figure 110. No thermal anomaly was present in satellite images at the N pit of Erta Ale for all of January and February 2022. At the S pit, a single weak anomaly was present during January, and a brighter single or double anomaly was present throughout February and early March. Sentinel-2 images use Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Figure 111. A weak thermal anomaly was present at the N pit of Erta Ale in the 29 March 2022 image (top right), and persisted in all of the April images (bottom). Double anomalies of consistent size and intensity, one bright and one dim, were present at the S pit in all images for March and April. Sentinel-2 images use Atmospheric penetration rendering (bands 12, 11, 8a). Courtesy of Sentinel Hub Playground.

Visitors to the S pit crater in late December 2021 and early January 2022 reported that the lake measured about 200 m in diameter and the level was about 30 m below the edge of the crater with fresh lava overhanging the crater rim (figure 112). Two collapses of the crater rim, widening the lake, were observed on 31 December-1 January 2022. In a second visit during 28-29 January 2022 the lake was still about 200 m in diameter with periodic small lava fountains (figure 113). On a 24 February 2022 visit the lava lake showed signs of constant activity with slabs of solidified crust moving around on the surface, bright orange lava in the cracks and spattering of lava a few tens of meters above the lake surface (figure 114).

Figure 112. Visitors to Erta Ale on 31 December-1 January 2022 reported that the crater at the S pit was about 200 m in diameter and the lava lake was about 30 m below the rim, with fresh lava hanging off the crater rim. Photo by Enku Mulugeta, courtesy of Volcano Discovery.

Figure 113. The lava lake at Erta Ale’s S pit crater was still about 200 m wide on 28 January 2022 and active with periodic lava fountains. Photo by Enku Mulugeta, courtesy of Volcano Discovery.

Figure 114. On a 24 February 2022 visit, Erta Ale’s lava lake at the S pit crater showed signs of constant activity with slabs of solidified crust moving around on the surface with bright orange lava in the cracks and spattering of lava a few tens of meters above the lake surface. Photo by Enku Mulugeta, courtesy of Volcano Discovery.

Geological Summary. The Erta Ale basaltic shield volcano in Ethiopia has a 50-km-wide edifice that rises more than 600 m from below sea level in the Danakil depression. The volcano includes a 0.7 x 1.6 km summit crater hosting steep-sided pit craters. Another larger 1.8 x 3.1 km wide depression elongated parallel to the trend of the Erta Ale range is located SE of the summit and is bounded by curvilinear fault scarps on the SE side. Basaltic lava flows from these fissures have poured into the caldera and locally overflowed its rim. The summit caldera usually also holds at least one long-term lava lake that has been active since at least 1967, and possibly since 1906. Recent fissure eruptions have occurred on the N flank.

Information Contacts: 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/); Sentinel Hub Playground (URL: https://www.sentinel-hub.com/explore/sentinel-playground); Tom Pfeiffer, Volcano Discovery (URL: http://www.volcanodiscovery.com/).