In BGVN 36:05, we reported that on 12 May 2011, the Vanuatu Geohazards Observatory (VGO) reported, based on information collected by the Vanuatu Meteorology and Geohazards Department, that a OMI (ozone monitoring instrument) satellite image showed strong degassing of SO₂ from Yasur volcano during the previous week (see map of this island volcano in figure 42 of BGVN 36:05). On 1 June 2011, the Vanuatu Volcano Alert Level (VVAL) was raised from 2 to 3, following increasing explosive activity during May, then lowered to 2 on 13 June (table 3).

Table 3. The Vanuatu Volcanic Alert Level (VVAL) scale for the six volcanoes monitored by Vanuato Geohazard Observatory (Yasur, Lopevi, Ambrym, Aoba, Gaua, and Suretamatai). Courtesy of Vanuatu Geohazards Observatory.

During the week of 7-12 July 2012, VGO observed that explosive activity at Yasur became stronger and more frequent, and shifted 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 (within the red zone, figure 43). 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 2012, the Alert Level was raised to 3.

VGO reported an OMI satellite image on 1 April 2013 showed diffuse SO₂ from Yasur. Explosive activity increased on 2 April 2013, with explosions becoming stronger and more frequent, and continued to slightly increase through 28 May. Bombs again fell around the summit area, the tourist walk, and the parking area. Moderate ash emissions and ashfall occurred on 2, 4, and 5 April, and 5 and 8 May 2013. Photos included in the report showed dense white plumes on 23 and 24 May. The Alert Level remained at 2 (on a scale of 0 4).

Volcano Ash Advisory Centre (VAAC) reports on Yasur. In many cases the VAAC lacked any satellite data and in cases where they did have data they frequently were unable to detect the plume or in other cases could not detect ash in the plume (table 4).

Table 4. Yasur volcano aviation reports (VAAs, Volcanic Ash Advisories) for the time interval 11 January 2009 to 10 June 2010. In many cases the information sources were the Vanuatu Geohazard Observatory (VGO). On 11 January the source was an AIREP, an aircraft report. Data provided courtesy of the Wellington Volcanic Ash Advisor Centre (VAAC).

Satellite Thermal Alerts. The MODIS/MODVOLC satellite thermal alert system has shown least 1 to 10 alerts each month over Yasur since the beginning of 2011. A lava lake has existed at Yasur for many years.

References. Allen, S.R., 2005, Complex spatter and pumice rich pyroclastic deposits from an andesitic caldera forming eruption:The Siwi pyroclastic sequence, Tanna, Vanuatu, Bulletin of Volcanology, v. 67, pp. 27 41.

Calmant, S., Pelletier, B., Lebellegard, P., Bevis, M., Taylor, F.W., and Phillips, D.A., 2003, New insights on the tectonics along the New Hebrides subduction zone based on GPS results, Journal of Geophysical Research, v. 108, no. B6, pp. 2319 2339.

Carnay, JN., and MacFarlane, A, 1979, Geology of Tanna, Aneityum, Futuna and Aniva, New Hebrides Geological Survey Report 1979, pp. 5 29.

Métrich, N., Allard, P., Aiuppa, A., Bani, P., Bertagnini, A., Shinohara, H., Parello, F., Di Muro, A., Garaebiti, E., Belhadj, O., and Massare, D., 2011, Magma and Volatile Supply to Post collapse Volcanism and Block Resurgence in Siwi Caldera (Tanna Island, Vanuatu Arc), Journal of Petrology, v. 52, no. 6, pp. 1077 1105; DOI: 10.1093/petrology/egr019.

Nairn, I.A., Scott, B.J., and Giggenbach, W.F., 1988, Yasur volcanic investigations, Vanuatu September 1988, New Zealand Geological Survey Report 1988, pp.1 74.

Pelletier, B., Calmant, S., and Pillet, R., 1998, Current tectonic of the Tonga New Hebrides region, Earth and Planetary Science Letters, v. 164, pp. 263 276.

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: Vanuatu Geohazards Observatory, Department of Geology, Mines and Water Resources of Vanuatu (URL: http://www.geohazards.gov.vu); NASA Earth Observatory (URL: http://earthobservatory.nasa.gov); MODIS/MODVOLC Thermal Alerts System, Hawai'i Institute of Geophysics and Planetology (HIGP), 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/); and Wellington Volcanic Ash Advisory Centre (VAAC), Meteorological Service of New Zealand Ltd (MetService), PO Box 722, Wellington, New Zealand (URL: http://www.metservice.com/vaac/, URL: http://vaac.metservice.com/).