Report on Ubinas (Peru) — December 1985
Scientific Event Alert Network Bulletin, vol. 10, no. 12 (December 1985)
Managing Editor: Lindsay McClelland.
Ubinas (Peru) Weak fumarolic activity
Please cite this report as:
Global Volcanism Program, 1985. Report on Ubinas (Peru) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 10:12. Smithsonian Institution.
16.355°S, 70.903°W; summit elev. 5672 m
All times are local (unless otherwise noted)
When geologists visited Ubinas on 12 August, fumarolic activity was weak and emissions were dilute. Some noise was coming from a pit about 300 m in diameter in the N side of the 1-km summit crater. . . .
Geologic Background. A small, 1.4-km-wide caldera cuts the top of Ubinas, Perú's most active volcano, giving it a truncated appearance. It is the northernmost of three young volcanoes located along a regional structural lineament about 50 km behind the main volcanic front. The growth and destruction of Ubinas I was followed by construction of Ubinas II beginning in the mid-Pleistocene. The upper slopes of the andesitic-to-rhyolitic Ubinas II stratovolcano are composed primarily of andesitic and trachyandesitic lava flows and steepen to nearly 45 degrees. The steep-walled, 150-m-deep summit caldera contains an ash cone with a 500-m-wide funnel-shaped vent that is 200 m deep. Debris-avalanche deposits from the collapse of the SE flank about 3,700 years ago extend 10 km from the volcano. Widespread Plinian pumice-fall deposits include one of Holocene age about 1,000 years ago. Holocene lava flows are visible on the flanks, but historical activity, documented since the 16th century, has consisted of intermittent minor-to-moderate explosive eruptions.
Information Contacts: M. Decobecq Dominique, Univ. Paris Sud, Orsay, France.