Report on Karkar (Papua New Guinea) — August 1989
Scientific Event Alert Network Bulletin, vol. 14, no. 8 (August 1989)
Managing Editor: Lindsay McClelland.
Karkar (Papua New Guinea) Summit deflation continues
Please cite this report as:
Global Volcanism Program, 1989. Report on Karkar (Papua New Guinea) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 14:8. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198908-251030.
Papua New Guinea
4.649°S, 145.964°E; summit elev. 1839 m
All times are local (unless otherwise noted)
"Ground deformation data obtained in July suggest continuing deflation of the summit area. Deflationary tilt changes of 35-75 µrad are indicated for the period November 1986-July 1989 by a group of stations at Karkar's summit. Data from the levelling line on the floor of the inner caldera indicate subsidence of the central part of the caldera floor relative to the E edge at a rate of ~5 mm/year since 1984.
"Eleven EDM lines were measured on the inner caldera network in July. Comparing these distances with November 1987 values, only four lines showed significant change (>20 ppm). All measurements from E Rim station are shorter than the 1987 values, indicating movement of this station toward the centre of the caldera (average movement ~40 mm NW). S rim station appears also to have moved inwards (by ~44 mm). These changes may be consistent with the subsidence and deflation indicated by levelling and dry tilt measurements."
Geologic Background. Karkar is a 19 x 25 km wide, forest-covered island that is truncated by two nested summit calderas. The 5.5-km-wide outer caldera was formed during one or more eruptions, the last of which occurred 9000 years ago. The eccentric 3.2-km-wide inner caldera was formed sometime between 1500 and 800 years ago. Parasitic cones are present on the N and S flanks of this basaltic-to-andesitic volcano; a linear array of small cones extends from the northern rim of the outer caldera nearly to the coast. Most historical eruptions, which date back to 1643, have originated from Bagiai cone, a pyroclastic cone constructed within the steep-walled, 300-m-deep inner caldera. The floor of the caldera is covered by young, mostly unvegetated andesitic lava flows.
Information Contacts: I. Itikarai and C. McKee, RVO.