Report on Yasur (Vanuatu) — 20 October-26 October 2021
Smithsonian / US Geological Survey Weekly Volcanic Activity Report,
20 October-26 October 2021
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2021. Report on Yasur (Vanuatu). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 20 October-26 October 2021. Smithsonian Institution and US Geological Survey.
19.532°S, 169.447°E; summit elev. 361 m
All times are local (unless otherwise noted)
The Vanuatu Meteorology and Geohazards Department (VMGD) reported that seismic activity slightly increased at Yasur beginning at 1330 on 22 October. Emissions also increased and large, dense ash-and-gas plumes were visible rising from the crater in webcam images at 1445. Increased ash emissions were confirmed during field observations later that day, prompting VMGD to expand the restricted area to a 1-km radius around the cone, defined by Danger Zone B on the hazard map. The Wellington VAAC noted that ash plumes rose as high as 1.2 km (4,000 ft) a.s.l. and drifted SE, E, and N during 22-24 October, based on webcam views and information from VMGD; emissions ceased by 1845 on 24 October. The Alert Level remained at 2 (on a scale of 0-4).
Geological Summary. Yasur, the best-known and most frequently visited of the Vanuatu volcanoes, has been in more-or-less continuous Strombolian and Vulcanian activity 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, this mostly unvegetated 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, horseshoe-shaped caldera 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.