Report on Ambrym (Vanuatu) — 20 July-26 July 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 20 July-26 July 2011
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2011. Report on Ambrym (Vanuatu). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 20 July-26 July 2011. Smithsonian Institution and US Geological Survey.
16.25°S, 168.12°E; summit elev. 1334 m
All times are local (unless otherwise noted)
Based on pilot observations and analyses of satellite imagery, the Wellington VAAC reported that on 19 July an ash plume from Ambrym rose to an altitude of 3 km (10,000 ft) a.s.l. and drifted 185 km NW.
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.