Report on Ambrym (Vanuatu) — 30 August-5 September 2017

Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 30 August-5 September 2017
Managing Editor: Sally Kuhn Sennert

Please cite this report as:

Global Volcanism Program, 2017. Report on Ambrym (Vanuatu). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 30 August-5 September 2017. Smithsonian Institution and US Geological Survey.

Volcano Profile |  Weekly Report (30 August-5 September 2017)


Ambrym

Vanuatu

16.25°S, 168.12°E; summit elev. 1334 m

All times are local (unless otherwise noted)


On 30 August the Vanuatu Geohazards Observatory (VGO) reported that “drastic changes” at Ambrym prompted an increase in the Alert Level from 2 to 3 (on a scale of 0-5). Areas deemed hazardous were near and around the active vents (Benbow, Maben-Mbwelesu, Niri-Mbwelesu and Mbwelesu), and in downwind areas prone to ashfall. According to a news article, a representative of VGO indicated that the Alert Level change was based on increased seismicity detected since the beginning of August but which became more notable on 25 August. Since monitoring of the volcano started around 20 years ago, the Alert Level had never been elevated past 2.

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.

Sources: Radio New Zealand, Vanuatu Meteorology and Geo-hazards Department