Report on Poas (Costa Rica) — 6 June-12 June 2012
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 6 June-12 June 2012
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2012. Report on Poas (Costa Rica) (Sennert, S, ed.). Weekly Volcanic Activity Report, 6 June-12 June 2012. Smithsonian Institution and US Geological Survey.
10.2°N, 84.233°W; summit elev. 2697 m
All times are local (unless otherwise noted)
OVSICORI-UNA reported that phreatic eruptions at Poás occurred on 6, 15, 20 and 26 May. The eruption on 15 May was preceded by about 6 hours of very-low amplitude harmonic tremor. Administrators of the Poás Volcano National Park witnessed the eruption and reported that sediment, water, rock fragments, and plumes were ejected 500 m above the lake surface. The level of the lake dropped ~0.9 m between 8 and 29 May.
Geological Summary. The broad vegetated edifice of Poás, one of the most active volcanoes of Costa Rica, contains three craters along a N-S line. The frequently visited multi-hued summit crater lakes of the basaltic-to-dacitic volcano are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the complex stratovolcano extends to the lower N flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, last erupted about 7,500 years ago. The more prominent geothermally heated northern lake, Laguna Caliente, is one of the world's most acidic natural lakes, with a pH of near zero. It has been the site of frequent phreatic and phreatomagmatic eruptions since an eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.