Sudden explosive eruption at Poas volcano, Costa Rica

Poas phreatic eruption April 7, 2022

A sudden explosive eruption took place at the northern part of Costa Rica’s Poas volcano at 08:42 UTC on April 6, 2022.

The eruption lasted about 3 minutes, generating a steam plume some 500 m (1 640 feet) above the crater (or 3 200 m / 10 500 feet a.s.l.).

The eruption came without any detectable precursors, such as increase in seismic activity or temperature of fumaroles which usually increase from 100 °C (212 °F) to 900 °C (1 652 °F).

Volcanologist Javier Pacheco from Costa Rica’s monitoring agency OVSICORI-UNA said the eruption seems to have not involved any new magma, but almost purely ejected steam. “It was likely a phreatic (steam-driven) explosion,” Pacheco said.1

Geologic summary 

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 2 708-m-high (8 884 feet) 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 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 the first historical eruption was reported in 1828. Eruptions often include geyser-like ejections of crater-lake water.2


1 Poás volcano: explosive eruption came without warning – QCostaRica

2 Poas – Geological summary – GVP

Featured image credit: OVSICORI-UNA


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