Report on Poas (Costa Rica) — 20 February-26 February 2019
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 20 February-26 February 2019
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2019. Report on Poas (Costa Rica). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 20 February-26 February 2019. 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 23-26 February seismicity at Poás was dominated by low-frequency events. Robust gas emissions rose from four fumarolic vents in the area previously covered by a lake, though the most vigorous emissions originated from vent A (Boca Roja). Minor incandescence from vent A was sometimes visible at night. A sulfur odor was reported in areas downwind including Naranjo, Zarcero, and Grecia (16 km SW). Particles of molten sulfur were included in ash deposits collected in Naranjo. Ashfall was reported in Canoas de Alajuela on 26 February.
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.