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Report on Irazu (Costa Rica) — November 1991

Bulletin of the Global Volcanism Network, vol. 16, no. 11 (November 1991)
Managing Editor: Lindsay McClelland.

Irazu (Costa Rica) Fumarolic activity declines

Please cite this report as:

Global Volcanism Program, 1991. Report on Irazu (Costa Rica). In: McClelland, L (ed.), Bulletin of the Global Volcanism Network, 16:11. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199111-345060.

Volcano Profile |  Complete Bulletin


Irazu

Costa Rica

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

All times are local (unless otherwise noted)


The turquoise-green crater lake continued to rise in November. Fumarolic activity, concentrated in the N part of the crater, diminished considerably, and stopped entirely at some sites. Some submerged fumaroles persisted subaqueously. A fumarole in the NW part of the crater had a temperature of 90°C and a condensate pH of 3.5, both similar to measurements during the previous 2 months.

Geologic Background. 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 and J. Barquero, OVSICORI.