Report on Poas (Costa Rica) — 10 May-16 May 2017
Smithsonian Institution / US Geological Survey
Weekly Volcanic Activity Report, 10 May-16 May 2017
Managing Editor: Sally Sennert.
Please cite this report as:
Global Volcanism Program, 2017. Report on Poas (Costa Rica) (Sennert, S, ed.). Weekly Volcanic Activity Report, 10 May-16 May 2017. 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 noted ash emissions at Poás on 10 May. Gas emissions were measured by an instrument mounted on a drone, revealing a gas plume rich in sulfur dioxide and low in carbon dioxide. During 10-11 May tremor amplitude was variable but low, and several volcano-tectonic events were detected. During 11-13 May tremor was constant, and volcano-tectonic and long-period events were detected; the seismicity possibly indicated small eruptions. Deformation was high, with vertical inflation of 3 cm since February.
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.