In our June 2012 Bulletin report (BGVN 37:06), we noted ongoing eruptions from Gaua during much of 2011.

On 5 December 2011, the Vanuatu Meteorology and Geohazards Department (VMGD) changed the status of Gaua volcano from a dormant to an active volcano. An index map showing Vanautu appears in the Ambrym report in this issue.

The Wellington Volcanic Ash Advisory Center (VAAC) reported that on 29 April 2013 a plume from Gaua was observed from an aircraft. Absent were further comments. Satellite imagery did not indicate ash. Astronauts on the International Space Station saw and photographed Gaua's E-blowing plume on 31 May 2013 (figure 24).

Figure 24. Steam plume from Gaua volcano as photographed from the International Space Station on 31 May 2013. For scale, the island is 20 km in diameter. Note N arrow at lower right. This is Astronaut photograph ISS036-E-5647, taken on Expedition 36 with a Nikon D3S digital camera using a 400 mm lens, and is provided by the ISS Crew Earth Observations experiment and the Image Science & Analysis Laboratory, Johnson Space Center. The image has been cropped and enhanced to improve contrast, and lens artifacts have been removed. The International Space Station Program supports the laboratory as part of the ISS National Lab to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Original caption was by William L. Stefanov, Jacobs/JETS at NASA-JSC.

The Alert Level of Gaua remained at level 1 (out of 4) signifying that changes in Gaua's activity could occur without, or with little, warning. VMGD continued this status through at least mid-August 2013, although they noted as slight increase in tremor since their June report.

This status indicates that ash falls will continue to be expected in areas exposed to trade winds. Strong degassing of the volcano could be accompanied with acid rainfall.

During the year ending in mid-July 2013, there were no MODVOLC thermal alerts.

Geologic Background. The roughly 20-km-diameter Gaua Island, also known as Santa Maria, consists of a basaltic-to-andesitic stratovolcano with an 6 x 9 km wide summit caldera. Small parasitic vents near the caldera rim fed Pleistocene lava flows that reached the coast on several sides of the island; several littoral cones were formed where these lava flows reached the sea. Quiet collapse that formed the roughly 700-m-deep caldera was followed by extensive ash eruptions. Construction of the historically active cone of Mount Garat (Gharat) and other small cinder cones in the SW part of the caldera has left a crescent-shaped caldera lake. The symmetrical, flat-topped Mount Garat cone is topped by three pit craters. The onset of eruptive activity from a vent high on the SE flank in 1962 ended a long period of dormancy.

Information Contacts: Vanuatu Geohazards Observatory (URL: http://www.vmgd.gov.vu/vmgd/); Vanuatu Meteorology and Geohazards Department (URL: http:// http://www.meteo.gov.vu/); Wellington Volcanic Ash Advisory Center (VAAC) (URL: vaac.metservice.com); and Hawai'i Institute of Geophysics and Planetology, MODVOLC Thermal Alert 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/).