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Report on Irazu (Costa Rica) — January 1992


Bulletin of the Global Volcanism Network, vol. 17, no. 1 (January 1992)
Managing Editor: Lindsay McClelland.

Irazu (Costa Rica) Crater lake shrinks; activity stops at some fumaroles but continues at others

Please cite this report as:

Global Volcanism Program, 1992. Report on Irazu (Costa Rica) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 17:1. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199201-345060


Costa Rica

9.979°N, 83.852°W; summit elev. 3432 m

All times are local (unless otherwise noted)

The water level in the main crater lake fell in January, following a rise of 1 m associated with heavy rains at the end of November. Although subaqueous and subaerial fumarolic activity continued unchanged along the N edge of the lake and crater wall, subaqueous fumaroles disappeared in the NE and SW parts of the lake in December. Fresh deposits from small landslides were observed on the NE and SW crater walls. A sulfur odor was strong on the SW crater rim, and vegetation S of the crater was partly "burned," probably due to acid rain and cold weather. Seismicity in January was at low levels, similar to December, with monthly totals of 29 low-frequency and 5 high-frequency earthquakes (recorded by OVSICORI).

Geological Summary. Irazú, one of Costa Rica's most active volcanoes, rises immediately E of the capital city of San José. The massive volcano covers an area of 500 km2 and is vegetated to within a few hundred meters of its broad flat-topped summit crater complex. At least 10 satellitic cones are located on its S flank. No lava flows have been identified since the eruption of the massive Cervantes lava flows from S-flank vents about 14,000 years ago, and all known Holocene eruptions have been explosive. The focus of eruptions at the summit crater complex has migrated to the W towards the historically active crater, which contains a small lake of variable size and color. Although eruptions may have occurred around the time of the Spanish conquest, the first well-documented historical eruption occurred in 1723, and frequent explosive eruptions have occurred since. Ashfall from the last major eruption during 1963-65 caused significant disruption to San José and surrounding areas.

Information Contacts: E. Fernández, V. Barboza, and J. Barquero, OVSICORI; G. Soto and R. Barquero, ICE.