Report on Poas (Costa Rica) — 4 May-10 May 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 4 May-10 May 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, 4 May-10 May 2011. Smithsonian Institution and US Geological Survey.
10.2°N, 84.233°W; summit elev. 2708 m
All times are local (unless otherwise noted)
OVSICORI-UNA reported that during April sporadic phreatic eruptions occurred from the central part of Laguna Caliente, a summit lake of Poás. Gas plumes rose a few meters to several tens of meters above the lake surface. Solid dark material ejected from the lake fell back into it, causing small surges. The temperature of the lava dome was 560 degrees Celsius at accessible areas. Bluish fumarolic plumes rose from the dome; a gas plume rose 1 km and drifted NE, E, and SE.
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.