Report on Yasur (Vanuatu) — January 1993
Bulletin of the Global Volcanism Network, vol. 18, no. 1 (January 1993)
Managing Editor: Lindsay McClelland
Yasur (Vanuatu) Ash-laden explosions and gas emission
Please cite this report as:
Global Volcanism Program, 1993. Report on Yasur (Vanuatu). In: McClelland, L (ed.), Bulletin of the Global Volcanism Network, 18:1. Smithsonian Institution. http://dx.doi.org/10.5479/si.GVP.BGVN199301-257100.
19.532°S, 169.447°E; summit elev. 361 m
All times are local (unless otherwise noted)
Observations from the W part of the crater rim on 28 October 1992 revealed low-level activity in Zone A, (S section of the crater) and substantial gas emission with faint explosions in Zone B (central section). Significant activity was observed in Zone C (N section) with large explosions and lava ejections reaching the rim. Explosions were heavily ash-laden and an ash cloud was clearly visible from the NW side of the volcano. Steam emission decreased through October because of low rainfall. A total of 21 earthquakes were recorded in 3 hours during 28 October fieldwork. The surface area of Lake Siwi had retreated by about one-third since the beginning of October and the river which feeds it had dried up.
On 8 November no significant explosive activity was observed. Small explosions with white gas emissions were observed in Zone A. No activity was observed in Zone B. There were heavy ash-laden gas emissions in Zone C. A continuous loud noise was heard from one of the vents, possibly in Zone C, which appeared to act as an escape valve, perhaps explaining the lack of significant explosive activity. Explosive activity resumed on 10 and 11 November, but was much less frequent and intense than in April, May, and October.
Geologic Background. 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.
Information Contacts: M. Lardy and D. Charley, LAVE.