Report on Ambrym (Vanuatu) — 18 February-24 February 2015
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 18 February-24 February 2015
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2015. Report on Ambrym (Vanuatu). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 18 February-24 February 2015. Smithsonian Institution and US Geological Survey.
16.25°S, 168.12°E; summit elev. 1334 m
All times are local (unless otherwise noted)
On 21 February the Vanuatu Geohazards Observatory issued a notice reminding the public that a minor eruption was occurring at Ambrym from a new vent inside the caldera. The Alert Level was raised to 3 (on a new scale of 0-5). Hazardous areas were identified as being near and around the active vents (Benbow, Maben-Mbwelesu, Niri-Mbwelesu and Mbwelesu), and in downwind areas prone to ashfall.
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.