Report on Poas (Costa Rica) — 2 August-8 August 2017
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 2 August-8 August 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, 2 August-8 August 2017. Smithsonian Institution and US Geological Survey.
10.2°N, 84.233°W; summit elev. 2708 m
All times are local (unless otherwise noted)
On 3 August OVSICORI-UNA reported that plumes of magmatic gases, water vapor, and aerosols continued to rise from Poás’s vent A (Boca Roja), and plumes of water vapor and abundant yellow particles of native sulfur were emitted from vent B (Boca Azufrada). Plumes rose as high as 1 km above the vents and drifted SSW. Incandescence from the bottom of the crater was recorded at night by the webcams. Recent measurements indicated that sulfur dioxide was emitted at a rate of 1,000-1,500 tons per day, which were values similar to those measured in the first months of 2017, before the phreato-magmatic eruptions of April and May. Gas plumes continued to rise from the vents and drift SW and NW at least through 8 August.
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.