Geologic Background:
Ubinas (also known as Uvinas and Uvillas) is
Peru's most active volcano. A small, 1.2-km-wide caldera
that cuts the top of Ubinas, Peru's most active volcano,
gives it a truncated appearance. The upper slopes of the
stratovolcano, composed primarily of Pleistocene
andesitic lava flows, steepen to nearly 45°. 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. Holocene lava flows cover its flanks.
Debris-avalanche deposits from the collapse of the SE
flank of Ubinas extend 10 km from the volcano. Widespread
Plinian pumice-fall deposits include some of Holocene
age. The eruption that formed the summit caldera left a
conspicuous 3-m-thick Plinian tephra. The summit crater
is 200-400 m deep, about 1.5 km in diameter, and hosts a
smaller inner crater. At least three Ubinas tephra-fall
layers postdate the 1600 AD eruption of Huaynaputina (a
volcanic center located 25 km to the south).
Historic Activity:
- At least 16 eruptions since 1550, the last in
1969.
- Holocene lava flows are visible on the volcano's
flanks, but historical activity, documented since the
16th century, has consisted of intermittent minor
explosive eruptions.
- In 1969, ashfall caused crop damage.
Recent Activity:
- The typical weak fumarolic activity began to increase
in December 1995 and was figorous during April 1996. This
led to designation of a hazard level of "Yellow".
Data Sources:
- Smithsonian's SEAN Bulletin (V. 10, No. 12)
- Global Volcanism Network (V. 21, No. 7).
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