Report on Ambrym (Vanuatu) — 17 April-23 April 2019
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 17 April-23 April 2019
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2019. Report on Ambrym (Vanuatu). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 17 April-23 April 2019. Smithsonian Institution and US Geological Survey.
16.25°S, 168.12°E; summit elev. 1334 m
All times are local (unless otherwise noted)
On 24 April the Vanuatu Meteorology and Geo-Hazards Department (VMGD) reported ongoing seismic activity at Ambrym and steam emissions. The lava lakes in Benbow and Marum craters had ceased to be active on 16 December 2018, one day after a fissure eruption began in the ESE part of the summit caldera near the Lewlembwi crater, and continued to be inactive. The Alert Level remained at 2 (on a scale of 0-5); the report reminded the public to stay outside of the Permanent Danger Zone defined as a 1-km radius from Benbow Crater and a 2-km radius from Marum Crater. An additional Danger Zone was defined as a 1-km radius around the December 2018 fissures.
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.