Report on Ubinas (Peru) — 26 April-2 May 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 26 April-2 May 2006
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2006. Report on Ubinas (Peru). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 26 April-2 May 2006. Smithsonian Institution and US Geological Survey.
16.355°S, 70.903°W; summit elev. 5672 m
All times are local (unless otherwise noted)
According to INGEMMET, on 22 April at 0715 an explosion began at Ubinas that produced an ash-and-gas plume that reached a height between 1 and 3 km above the volcano (or 21,900 and 28,450 ft a.s.l.). This was the highest rising plume since activity began in late March. Continuous emissions occurred until 1600. Ash and gas emitted during 20-22 April traveled as far as 60 km from the volcano mainly NW, W, and SW, and traces of ash reached the Arequipa airport. During 25 and 26 April, the volume of ash emitted from the volcano decreased significantly. Gas plumes rose between 200 and 700 m above the volcano's caldera (or 19,300 and 20,900 ft a.s.l.). The Alert Level was reduced from Orange to Yellow. Seismicity during 22-26 April was higher than normal. The Buenos Aires VAAC posted volcanic ash advisories during the report period.
Geologic Background. A small, 1.4-km-wide caldera cuts the top of Ubinas, Peru'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 of Perú. 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 3700 years ago extend 10 km from the volcano. Widespread plinian pumice-fall deposits include one of Holocene age about 1000 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.