Geologic Background:
Karkar is a forest-covered island 19 x 25 km
wide with two nested summit calderas. It is locate about
16 km off the north coast of New Guinea across the
Isumrud Strait from Cape Croisilles, 100 km eastsoutheast
of Manam. Parasitic cones are present on the north and
south flanks. The 5.5-km-wide outer caldera was formed
during one or more eruptions, the last of which occurred
9,000 years ago. The excentric 3.2-km-wide inner caldera
was formed sometime between 1,500 and 800 years ago.
Parasitic cones are present on the northern and southern
flanks of Karkar; a linear array of small cones extends
from the northern rim of the outer caldera nearly to the
coast. The Bagiai cone is a pyroclastic cone constructed
within the steep-walled, 300-m-deep inner caldera. The
floor of the caldera is covered by young, mostly
unvegetated lava flows.
Historic Activity:
- Nine eruptions are known since 1643.
- Most historical eruptions have originated from Bagiai
cone within the 300-m-deep, 3.2-km-wide younger caldera,
whose floor is largely covered by young lava flows.
Recent Activity:
- A strong explosive eruption occurred in early 1979,
with phreatic activity continuing into 1980. A decade
after the eruption, revegetation of the crater was
proceeding, and fumarolic activity had declined. The
overall picture gained over the last few years
(1990-1992) of measurement at Karkar is of a gradual
progression into dormancy. Vegetation is rapidly being
re-established on the caldera floor and walls, on Bagiai
cone, and in the crater produced by the 1979
eruption.
- Sharp increase in seismicity from mid-May to mid-June
1994. A second seismic swarm occurred on Oct. 18.
Data Sources:
- Smithsonian's SEAN Bulletin (V. 3, No. 9 and V. 14,
No. 8)
- Global Volcanism Network (V. 15, No. 9 to V. 25, No.
11).
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