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. (source: volcano.si.edu)



Ambrym Volcano (Vanuatu)
16.25 S, 168.12 E, summit elevation 1334 m, Pyroclastic Shield Volcano
Wednesday 20th April 2005
Ambrym volcano has produced the strongest point source of sulfur dioxide on the planet for the first months of 2005. The volcano has been erupting in a more destructive manner than usual for the past year, and producing high sulfur dioxide emissions for at least six months. During the first ten days of March 2005, data collected by the Ozone Monitoring Instrument on NASA’s Aura satellite showed high concentrations of sulfur dioxide drifting northwest from the volcano. Visual observations of the volcano at the end of March by John Seach recorded a strong night glow at Benbow, and the sound of bubbling lava could be heard deep in the crater, accompanied by continuous light-brown ash emissions. The volcano still poses a hazard to the local population with ashfall and acid rain affecting food crops and drinking water. During January 2005 many residents were burnt from acid rain and required medical assistance. Report by John Seach.
(source : volcanolive)