Report on Ambrym (Vanuatu) — June 2004
Bulletin of the Global Volcanism Network, vol. 29, no. 6 (June 2004)
Managing Editor: Richard Wunderman.
Ambrym (Vanuatu) Continued MODVOLC thermal alerts indicating activity, January 2003-May 2004
Please cite this report as:
Global Volcanism Program, 2004. Report on Ambrym (Vanuatu). In: Wunderman, R (ed.), Bulletin of the Global Volcanism Network, 29:6. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN200406-257040.
16.25°S, 168.12°E; summit elev. 1334 m
All times are local (unless otherwise noted)
Ambrym triggered continued alerts during 2003 and 2004 at both Marum and Benbow craters, with Marum alerts being the slightly more common (figures 12 and 13). Activity appeared less intense than in previous years, but more alerts were issued due to the availability of Aqua data starting from January 2004. The highest alert ratio (-0.088) (see BGVN 28:01 for a discussion of the alert ration) was detected by Aqua on 14 May 2004 and the highest number of alert pixels detected for any one pass was four, a situation repeated on 29 June, 21 August, and 2 November 2003. Visual observations during September 2003 (BGVN 28:09) confirmed that there was activity at these craters.
Data acquisition and analysis. Reports from Diego Coppola and David A. Rothery provided analyses of MODIS thermal alerts during 2001 and 2002 (using the MODVOLC alert-detection algorithm) extracted from the MODIS Thermal Alerts website (http://modis.hgip.hawaii.edu/) maintained by the University of Hawaii HIGP MODIS Thermal Alerts team (BGVN 28:01). Rothery and Charlotte Saunders provided updates to 31 May 2004. MODVOLC data are now routinely available from the Aqua satellite (equator crossing times 0230 and 1430 local time) in addition to the original Terra satellite (equator crossing times 1030 and 2230 local time).
Geologic Background. Ambrym, a large basaltic volcano with a 12-km-wide caldera, is one of the most active volcanoes of the New Hebrides arc. A thick, almost exclusively pyroclastic sequence, initially dacitic, then basaltic, overlies lava flows of a pre-caldera shield volcano. The caldera was formed during a major plinian eruption with dacitic pyroclastic flows about 1900 years ago. Post-caldera eruptions, primarily from Marum and Benbow cones, have partially filled the caldera floor and produced lava flows that ponded on the caldera floor or overflowed through gaps in the caldera rim. Post-caldera eruptions have also formed a series of scoria cones and maars along a fissure system oriented ENE-WSW. Eruptions have apparently occurred almost yearly during historical time from cones within the caldera or from flank vents. However, from 1850 to 1950, reporting was mostly limited to extra-caldera eruptions that would have affected local populations.
Information Contacts: David A. Rothery and Charlotte Saunders, Department of Earth Sciences, The Open University, Milton Keynes, MK7 6AA, United Kingdom.