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Report on Irazu (Costa Rica) — November 1982


Scientific Event Alert Network Bulletin, vol. 7, no. 11 (November 1982)
Managing Editor: Lindsay McClelland.

Irazu (Costa Rica) Sulfur odors now always detectable in the summit region

Please cite this report as:

Global Volcanism Program, 1982. Report on Irazu (Costa Rica) (McClelland, L., ed.). Scientific Event Alert Network Bulletin, 7:11. Smithsonian Institution. https://doi.org/10.5479/si.GVP.SEAN198211-345060


Costa Rica

9.979°N, 83.852°W; summit elev. 3436 m

All times are local (unless otherwise noted)

"Some indications that Irazú may be becoming more active were noted in several trips to the summit. The smell of H2S, only occasionally noticeable in November-December 1981 and again in January 1982, was always detectable in the summit region. On 22 November a small flow of molten sulfur was observed to have advanced several meters from a fumarole at the base of the N wall of the active crater. Park guards believed that it was new that day.

"Faulting and slumping of scarps were reported to have occurred over a large area of the summit during November. This was largely confined to a belt oriented NE-SW and ~3-4 km from the summit crater. Park guards reported a single day in September in which 20-30 earthquakes were felt."

Geological Summary. The massive Irazú volcano in Costa Rica, immediately E of the capital city of San José, covers an area of 500 km2 and is vegetated to within a few hundred meters of its broad summit crater complex. At least 10 satellitic cones are located on its S flank. No lava effusion is known since the eruption of the 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 main crater, which contains a small lake. The first well-documented 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. Phreatic activity reported in 1994 may have been a landslide event from the fumarolic area on the NW summit (Fallas et al., 2018).

Information Contacts: R. Stoiber, S. Williams, H.R. Naslund, C. Connor, J. Prosser, and J.B. Gemmell, Dartmouth College; E. Malavassi R. and J. Barquero H., Univ. Nacional, Heredia.