Report on Poas (Costa Rica) — 24 May-30 May 2017

Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 24 May-30 May 2017
Managing Editor: Sally Kuhn Sennert

Please cite this report as:

Global Volcanism Program, 2017. Report on Poas (Costa Rica). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 24 May-30 May 2017. Smithsonian Institution and US Geological Survey.

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Poas

Costa Rica

10.2°N, 84.233°W; summit elev. 2708 m

All times are local (unless otherwise noted)


OVSICORI-UNA reported that tremor amplitude at Poás fluctuated between low and high levels during 23-30 May, often corresponding to the vigor of emissions of water vapor, magmatic gases, and material from fumarolic vents. During 25-26 May ashfall was reported in some communities around the volcano. Low magnitude volcano-tectonic earthquakes and small phreatic eruptions were recorded sporadically during 27-30 May.

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.

Source: Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional (OVSICORI-UNA)