Report on Poas (Costa Rica) — July 1985
Scientific Event Alert Network Bulletin, vol. 10, no. 7 (July 1985)
Managing Editor: Lindsay McClelland.
Poas (Costa Rica) Fumarole temperatures drop
Please cite this report as:
Global Volcanism Program, 1985. Report on Poas (Costa Rica) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 10:7. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198507-345040.
Poas
Costa Rica
10.2°N, 84.233°W; summit elev. 2708 m
All times are local (unless otherwise noted)
Activity was characterized by the emission of gas from fumaroles on the eroded 1953-55 cone. Fumarole temperatures continued to drop, while crater lake temperature remained constant (table 3).
Table 3. Temperatures (in °C) measured in a fissure on the E side of the eroded 1953-55 cone and in the crater lake, January 1982-October 1985.
| Date | Fumarole Temperature | Crater Lake Temperature | Lake Water pH |
| Jan 1982 | 860 | 47 | -- |
| Feb 1982 | 883 | 48 | -- |
| Mar 1982 | 887 | 47 | -- |
| Apr 1982 | 873 | 50 | -- |
| Dec 1982 | 731 | 40 | -- |
| Jan 1983 | 753 | 56 | -- |
| Feb 1983 | 732 | 60 | -- |
| Mar 1983 | 780 | 60 | -- |
| Apr 1983 | 818 | 60 | -- |
| May 1983 | 832 | 57 | 0.06 |
| Jun 1983 | 834 | 57 | 0.1 |
| Jul 1983 | 822 | 57 | 0.2 |
| Aug 1983 | 806 | 58 | 0.2 |
| Sep 1983 | 810 | 58 | 0.3 |
| Oct 1983 | 801 | 60 | 0.6 |
| Nov 1983 | 750 | 58 | -- |
| Dec 1983 | 750 | 56 | 0.07 |
| Jan 1984 | 690 | 51 | 0.7 |
| Feb 1984 | 650 | 51 | -- |
| Mar 1984 | 570 | 54 | 0.7 |
| Apr 1984 | 570 | 49 | -- |
| May 1984 | 586 | 50 | -- |
| Jun 1984 | 603 | 50 | -- |
| Jul 1984 | 602 | 48 | -- |
| Aug 1984 | 530 | 48 | -- |
| Sep 1984 | 500 | 50 | -- |
| Oct 1984 | 490 | 48 | -- |
| Nov 1984 | 510 | 48 | -- |
| Dec 1984 | 515 | 48 | -- |
| Jan 1985 | 550 | 44 | -- |
| Feb 1985 | 560 | 44 | -- |
| Mar 1985 | 584 | 44 | -- |
| Apr 1985 | 568 | 44 | -- |
| May 1985 | 490 | 44 | -- |
| Jun 1985 | 420 | 48 | -- |
| Jul 1985 | 316 | 46 | -- |
| Aug 1985 | 295 | 45 | -- |
| Sep 1985 | 294 | 45 | -- |
| Oct 1985 | 310 | 45 | -- |
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.
Information Contacts: J. Barquero H. and E. Fernández S., Univ. Nacional, Heredia.
