Report on Ubinas (Peru) — 5 April-11 April 2006
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 5 April-11 April 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, 5 April-11 April 2006. Smithsonian Institution and US Geological Survey.
16.355°S, 70.903°W; summit elev. 5672 m
All times are local (unless otherwise noted)
Based on information from the Perúvian Volcanologic Observatory, the Buenos Aires VAAC reported that ash emitted from Ubinas reached 6.1-9.1 km (20,000-30,000 ft) a.s.l. on 6 April around 1220. No ash was visible on satellite imagery. The Aviation Color Code for the volcano was at Red, the highest level. At 1900 on the 6th a plume was observed at 6.1-7.3 km (20,000-24,000 ft) a.s.l. and drifting NE. The Aviation Color Code was subsequently reduced to Orange. On 8 April the VAAC received a report that volcanic activity had ceased, so the Aviation Color Code was reduced to Green, the lowest level. On the 9th, a significant meteorological forecast (SIGMET) was issued for an ash cloud at a height of 6.1-7.3 km (20,000-24,000 ft) a.s.l. that was drifting SW. The Aviation Color Code was increased to Red until 11 April. On the 11th volcanic activity reportedly ceased, so the code was again decreased to Green.
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.