Lewotolok (also known as Lewotolo) is located on the island of Lembata (Lomblen) in the Lesser Sunda Islands of Indonesia. Eruptions have been recorded since 1660 and have primarily consisted of explosive activity from the summit crater. More recent activity has been characterized by Strombolian explosions and intermittent ash plumes (BGVN 48:05). This report covers frequent ash plumes and gas-and-steam emissions during May through October 2023, based on information provided by Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as CVGHM, or the Center of Volcanology and Geological Hazard Mitigation), MAGMA Indonesia, the Darwin Volcanic Ash Advisory Centre (VAAC), and satellite data.

Daily white and white-and-gray plumes rose as high as 800 m above the summit and drifted in multiple directions during May and June. Webcam images occasionally showed incandescent material ejected above the summit, accompanied by crater incandescence. Intermittent ash plumes were recorded during 2-3 (figure 48), 5-6, 9, 11, 15-16, 20, 22-24, and 27-29 May. They rose 400-800 m above the crater and drifted in different directions. During June, ash plumes were detected during 1-2, 5, 7, 9, 12, 17-18, and 27 June, rising 300-1,000 m above the summit and drifting W, NW, and SW. Strombolian explosions were visible at the summit crater at 2242 on 14 June, at 2137 on 17 June, and at 2213 on 18 June (figure 49), based on webcam images.

Figure 48. Webcam image showing a gray ash plume rising above Lewotolok, taken at 1737 on 2 May 2023. The ash plume rose several hundred meters above the summit. Courtesy of MAGMA Indonesia.

Figure 49. Webcam image of a Strombolian explosion at Lewotolok, taken at 2213 on 18 June 2023. Image has been color corrected. Courtesy of MAGMA Indonesia.

During July and August daily white and white-and-gray plume continued, rising as high 800 m above the summit, and drifting generally W and NW. Crater incandescence was also intermittently visible in clear webcam images. Ash plumes were reported on 11, 27, and 31 July that rose 400 m, 500 m, and 500 m above the summit and drifted W, NW, and W, respectively. During August, ash plumes were observed on 12, 14, 17, 20 (figure 50), 23-24, 26, and 30 August. They rose 600-800 m above the summit and drifted W, NW, N, and NW.

Figure 50. Webcam image of an ash plume rising several hundred meters above Lewotolok, taken at 1735 on 20 August 2023. Photo has been color corrected. Courtesy of MAGMA Indonesia.

Similar daily white and white-and-gray plumes persisted during September and October. Occasional webcam images captured incandescent material ejected above the summit accompanied by crater incandescence. Plumes rose 25-700 m above the summit and generally drifted W and NW. Ash plumes were reported during 1-3 (figure 51), 12, 14, 19, 20-21, 23-24, and 28-29 September and 1-3, 5-6, 11-13, 17, 19-21, 23-26, and 29 October. The ash plumes rose 500-800 m above the summit and drifted generally W and NW during September and rose 300-700 m above the summit and drifted generally W and NW during October.

Figure 51. Webcam image of an ash plume rising several hundred meters above Lewotolok, taken at 1734 on 3 September 2023. Photo has been color corrected. Courtesy of MAGMA Indonesia.

Thermal activity was consistent throughout the reporting period, often characterized by incandescent ejecta, crater incandescence, and some Strombolian explosions. Thermal activity based on MIROVA (Middle InfraRed Observation of Volcanic Activity) data showed frequent moderate thermal anomalies during late May through October (figure 52). According to the MODVOLC thermal algorithm, a total of 51 hotspots were detected on 28 May, 1, 7, 12, 14, 19, 26, 27, and 29 June, 3, 8, 9, 18, 20, 25, 27, and 30 July, 1, 8, 11, 16, 22, 25, and 30 August, 23, 24, 28, 29, and 30 September, and 1, 5, 6, 8, 13, 15, 17, 18, and 20 October. Some of this activity was reflected in infrared satellite imagery on clear weather days; it captured crater incandescence and incandescent ejecta that was deposited on the upper flanks of the volcano (figure 53).

Figure 52. Frequent moderate thermal activity was detected at Lewotolok during May through October 2023, as shown by this MIROVA plot (Log Radiative Power). Thermal activity was relatively low during early May, but it increased in both frequency and power by late May and remained elevated through the reporting period. Courtesy of MIROVA.

Figure 53. Infrared (bands B12, B11, B4) satellite images showed a strong and persistent thermal anomaly (bright yellow-orange) at the summit crater of Lewotolok on 28 May 2023 (top left), 7 June 2023 (top right), 7 July 2023 (left middle), 16 August 2023 (right middle), 25 September 2023 (bottom left), and 15 October 2023 (bottom right). Some incandescent material was visible on the upper flanks of the volcano. Courtesy of Copernicus Browser.

Geological Summary. The Lewotolok (or Lewotolo) stratovolcano occupies the eastern end of an elongated peninsula extending north into the Flores Sea, connected to Lembata (formerly Lomblen) Island by a narrow isthmus. It is symmetrical when viewed from the north and east. A small cone with a 130-m-wide crater constructed at the SE side of a larger crater forms the volcano's high point. Many lava flows have reached the coastline. Eruptions recorded since 1660 have consisted of explosive activity from the summit crater.

Information Contacts: Pusat Vulkanologi dan Mitigasi Bencana Geologi (PVMBG, also known as Indonesian Center for Volcanology and Geological Hazard Mitigation, CVGHM), Jalan Diponegoro 57, Bandung 40122, Indonesia (URL: http://www.vsi.esdm.go.id/); MAGMA Indonesia, Kementerian Energi dan Sumber Daya Mineral (URL: https://magma.esdm.go.id/v1); 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/); Copernicus Browser, Copernicus Data Space Ecosystem, European Space Agency (URL: https://dataspace.copernicus.eu/browser/).