Report on Poas (Costa Rica) — 9 November-15 November 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 9 November-15 November 2011
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2011. Report on Poas (Costa Rica). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 9 November-15 November 2011. 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 October fumarolic activity at Poás continued with bluish gas plumes rising from the lava dome; plumes rose more than 1 km and were reported by residents in Valle Central. Towards the end of the month, the fumarolic activity as well as incandescence from the lava dome decreased. The new craters at the N base of the dome united into a crater that was 25 m long and 7-10 m wide. Phreatic activity continued to occur from Laguna Caliente, the summit lake. The lake was 55 degrees Celsius, and the level had risen 22 cm between 14 September and 27 October.
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.