Report on Irazu (Costa Rica) — October 1991
Bulletin of the Global Volcanism Network, vol. 16, no. 10 (October 1991)
Managing Editor: Lindsay McClelland.
Irazu (Costa Rica) Fumarole temperatures and seismicity decline
Please cite this report as:
Global Volcanism Program, 1991. Report on Irazu (Costa Rica) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 16:10. Smithsonian Institution.
9.979°N, 83.852°W; summit elev. 3432 m
All times are local (unless otherwise noted)
Fumarolic activity continued within the crater through October, with no significant changes, although there was an apparent slight temperature decrease from 90.0-91.6°C in September, to 83.8-90.4°C in October. The hottest and most vigorous fumarole was located in an alluvial fan on the crater's N side. Crater lake level increased in September, and stabilized through October at a maximum depth of 14 m. Small fluctuations were noted, corresponding with rainfall. Seismicity continued to decline in September, reaching very low levels in October.
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: R. Barquero and G. Soto, ICE.