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Report on Ubinas (Peru) — December 1985


Ubinas

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. https://doi.org/10.5479/si.GVP.SEAN198512-354020



Ubinas

Peru

16.345°S, 70.8972°W; summit elev. 5608 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. . . .

Geological Summary. The truncated appearance of Ubinas, Perú's most active volcano, is a result of a 1.4-km-wide crater at the summit. 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°. The steep-walled, 150-m-deep summit crater 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 from about 1,000 years ago. Holocene lava flows are visible on the flanks, but 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.