Report on Poas (Costa Rica) — 31 August-6 September 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 31 August-6 September 2011
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2011. Report on Poas (Costa Rica). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 31 August-6 September 2011. Smithsonian Institution and US Geological Survey.
10.2°N, 84.233°W; summit elev. 2708 m
All times are local (unless otherwise noted)
On 31 August OVSICORI-UNA reported that since mid-July incandescence was visible during the day on the lava dome of Poás, which had not occurred since 1981, and was the result of changes in activity that had started several months before. OVSICORI-UNA speculated that the changes could be either from recent magma intrusion or a change in the hydrothermal plumbing system and noted the need to further analyze data from seismic, deformation, geochemical, and field measurements.
Geologic Background. The broad, well-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, which is one of Costa Rica's most prominent natural landmarks, are easily accessible by vehicle from the nearby capital city of San José. A N-S-trending fissure cutting the 2708-m-high complex stratovolcano extends to the lower northern flank, where it has produced the Congo stratovolcano and several lake-filled maars. The southernmost of the two summit crater lakes, Botos, is cold and clear and last erupted about 7500 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 the first historical eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.