April 6, 2004
During March, an active lava lake was observed within Mbwelesu crater.
This information was summarized from the GVP/USGS Weekly Volcanic Activity Report
General map of Ambrym showing the main volcanic features (caldera, cones, maars, and fissures). Ambrym is the most voluminous active volcano in Vanuatu. Marum and Benbow are post-caldera cones. The caldera is similar in size to calderas associated with large Plinian eruptions. From Robin and others (1993).
Ambrym Island is a large shield volcano with a caldera. The caldera formed in about 50 A.D. with an eruption of VEI 6. It is also a very active volcano with 48 eruptions since 1774. Most of these eruptions are at cones inside of a caldera (5.5 by 7.5 miles; 9 by 12 km).The eruptions are explosive and usually from a central vent, There have been a few flank eruptions. Fifteen erupts produced lava flows. Ten eruptions involved a lava lake. There were fatalities in two eruptions at Ambrym. In 1894, six people were killed by volcanic bombs and four people were overtaken by lava flows. In 1913, 21 people were killed during an explosive eruption. Acid rainfall in 1979 burned some of the inhabitants. Local water supplies were contaminated and had a pH of 5.2-5.5.
View of the ash plain from a ridge on Benbow. The caldera rim is in the distance on the right. The caldera is about 7.5 miles (12 km) in diameter. Photograph courtesy of Mike Lyvers.
Cross-section of Ambrym showing the basal shield volcano (black), the 12-km lateral extent of the large basaltic tuff cone (yellowish gray), and the post-caldera volcanic rocks (medium gray). Normal faults offset blocks of the tuff cone and shield volcano. Vertical exaggeration = 3 x. From Robin and others (1993).
View inside Benbow's crater. The crater contains a lava lake. Photograph courtesy of Mike Lyvers.
Crater 3 at Marum, another of Ambrym's main vents. The crater is about 1,000 feet (300 m) deep. Photograph courtesy of Mike Lyvers.
Wide-angle view of the interior of crater 3 with lava lake. Photograph courtesy of Mike Lyvers.
Closeup of the lava lake. Mike Lyvers reported "Thunderous explosions occurred every 10 minutes or so, engulfing me in foul gases and warm glassy filaments pf Pele's hair which also covered the ground like spider webs at the craters edge." Photograph courtesy of Mike Lyvers.
Mike Lyvers: Volcano ListServ, personal communication
McCall, G.J.H., LeMaitre, R.W., Malahoff, A., Robinson, G.P., and Stephenson, P.J., 1970, The geology and geophysics of Ambrym caldera, New Hebrides: Bulletin of Volcanology, v. 34, p. 681-696.
Robin, C., Eissen, J-P., and Monzier, M., 1993, Giant tuff cone and 12-km-wide associated caldera at Ambrym volcano (Vanuatu, New hebrides arc: Journal of Volcanology and Geothermal Research, v. 55, p. 225-238.
Simkin, T., and Siebert, L., 1994, Volcanoes of the World: Geoscience Press, Tucson, Arizona, 349 p.
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