Yasur, the southernmost active volcano in Vanuatu, has been erupting since at least 1774 with frequent Strombolian explosions and ash and gas plumes from several vents in the 400-m-diameter summit crater (BGVN 47:09). This report summarizes activity during May-October 2023, using information from bulletins of the Vanuatu Meteorology and Geo-Hazards Department (VMGD) and various satellite data. According to VMGD, Yasur (also called Tanna, after the island on which it is located) has remained on Alert Level 2 (major unrest state, on a scale of 0-5) since 18 October 2016, and VMGD warned the public not to enter the restricted area within a radius of 600 m around the cone (Danger Zone A on the VMGD’s Caldera Safety Map).

Low-to-moderate Strombolian explosions continued through the reporting period, ejecting bombs that landed back into the crater and producing steam, gas, and ash emissions. Larger explosions occasionally ejected material outside of the crater. During 1400-1700 on 12 September the volcano emitted a substantial ash plume that drifted SE; activity returned to normal the next day. During October, satellites detected an increase in steam, gas, and ash emissions from the summit crater. On 10 October, a significant landslide occurred inside a crater vent.

Sentinel-2 images during May-October 2023 clearly showed lava effusion from multiple vents within the summit crater every day when weather clouds did not obstruct views (figure 89). Consistent with these observations, the MIROVA hotspot detection system recorded persistent thermal anomalies (figure 90). The MODIS-MODVOLC thermal detection system recorded hotspots on 5-7 days per month during May-July, but only on two days in August and none in September and October 2023. Small sulfur dioxide plumes were frequently detected by the TROPOMI instrument on the Sentinel-5P satellite drifting in different directions (figure 91).

Figure 89. Sentinel-2 images of Yasur showing strong thermal anomalies on 15 May 2023 from multiple vents within the summit crater (left, false color bands 12, 11, 4), and a gas emission on 9 July 2023 (right, true color bands 4, 3, 2). Courtesy of the Copernicus Browser.

Figure 90. MIROVA (Log Radiative Power) graph of thermal data for Yasur during the year ending in March 2024, showed persistent low-to-moderate power thermal anomalies detected by MODIS instruments during May-August; both their frequency and intensity dwindled during September and October. Courtesy of MIROVA.

Figure 91. Small sulfur dioxide plumes from Yasur were frequently detected by the TROPOMI instrument on the Sentinel-5P satellite during May-October 2023, as shown in representative images on 8 July (left) and 3 September (right) 2023. Courtesy of the NASA Global Sulfur Dioxide Monitoring Page.

Geological Summary. Yasur has exhibited essentially continuous Strombolian and Vulcanian activity at least since Captain Cook observed ash eruptions in 1774. This style of activity may have continued for the past 800 years. Located at the SE tip of Tanna Island in Vanuatu, this pyroclastic cone has a nearly circular, 400-m-wide summit crater. The active cone is largely contained within the small Yenkahe caldera, and is the youngest of a group of Holocene volcanic centers constructed over the down-dropped NE flank of the Pleistocene Tukosmeru volcano. The Yenkahe horst is located within the Siwi ring fracture, a 4-km-wide open feature associated with eruption of the andesitic Siwi pyroclastic sequence. Active tectonism along the Yenkahe horst accompanying eruptions has raised Port Resolution harbor more than 20 m during the past century.

Information Contacts: Geo-Hazards Division, Vanuatu Meteorology and Geo-Hazards Department (VMGD), Ministry of Climate Change Adaptation, Meteorology, Geo-Hazards, Energy, Environment and Disaster Management, Private Mail Bag 9054, Lini Highway, Port Vila, Vanuatu (URL: http://www.vmgd.gov.vu/, https://www.facebook.com/VanuatuGeohazardsObservatory/); 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, Maryland, USA (URL: https://so2.gsfc.nasa.gov/); Copernicus Browser (URL: https://dataspace.copernicus.eu/browser).