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.
Historic Activity:
- At least 25 eruptions from 1774 to 1979.
- Ambrym has been almost continuously active since its
discovery by Captain Cook in 1774. During that time it
has had Strombolian and Plinian activity, standing lava
lakes, and produced numerous lava flows.
- 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.
Recent Activity:
- On March 8, 1986 an ash plume reached an altitude of
3000 meters. Activity in Nov. 1986 formed a new cone and
produced an intra-calders lava flow. Lava lake activity
from May to August 1988.
- Large plume rising about 3500 meters was reported in
April 1989 along with continued lava flow activity.
- Activity was continuing in Nov. 1990, but lava lake
had disappeared.
- Activity has been more or less constant since
1990.
- A 2 km high ash cloud extending 50 km from crater was
reported on June 10, 1991. Aerial surveys on July 13 and
24, 1991 reported active lava lake.
- Aerial survey on Dec. 7, 1994 reported active lava
lakes in Benbow and Marum craters.
- Aerial survery on July 22, 1996 confirmed activity in
lava lakes in Benbow and Marum craters.
- During a visit on Aug 5-13, 1997 lava flows and
fountains were observed
- Activity continued through 1999 into 2000.
Data Sources:
- Smithsonian's SEAN Bulletin (V. 4, No. 3 to V. 14,
No. 10)
- Global Volcanism Network (V. 15, No. 11 to V. 26, No.
2).
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