Report on Yasur (Vanuatu) — 25 July-31 July 2012
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 25 July-31 July 2012
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2012. Report on Yasur (Vanuatu). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 25 July-31 July 2012. Smithsonian Institution and US Geological Survey.
19.532°S, 169.447°E; summit elev. 361 m
All times are local (unless otherwise noted)
Following an assessment during 7-12 July, the Geohazards Observatory team concluded that explosive activity at Yasur had slightly increased, becoming stronger and more frequent, and shifting from Strombolian to sub-Plinian. Bombs ejected from the vents fell in the crater, around the summit area, and on the tourist walk and parking area. The explosions were heard, felt, and observed from nearby villages and schools. Activity at all three volcanic vents was characterized by degassing, ash emissions, and ejection of bombs. On 13 July the Alert Level was raised to 3 (on a scale of 0-4).
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.