Report on Irazu (Costa Rica) — January 1996
Bulletin of the Global Volcanism Network, vol. 21, no. 1 (January 1996)
Managing Editor: Richard Wunderman.
Irazu (Costa Rica) Dark yellow crater-lake water; discrete 7-hour seismic swarm
Please cite this report as:
Global Volcanism Program, 1996. Report on Irazu (Costa Rica). In: Wunderman, R. (ed.), Bulletin of the Global Volcanism Network, 21:1. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199601-345060.
9.979°N, 83.852°W; summit elev. 3432 m
All times are local (unless otherwise noted)
When visited in January, the crater lake's dark-yellow water remained high, covering the entire crater floor. Prominent fumaroles continued to bubble along the lake's N, NW, and SE shores. Slides continued to take place along the N, SW, and W walls. Seismic station IRZ2 (5 km SW) registered a swarm of 29 local earthquakes between 1512 and 2111 on 30 January; one was detected at a more distant station.
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: Rodolfo Van der Laat, Vilma Barboza, Erick Fernández, Jorge Barquero, Franklin de Obaldia, Tomás Marino, and Rodrigo Sáenz, Observatorio Vulcanológico y Sismológico de Costa Rica, Universidad Nacional (OVSICORI-UNA), Apartado 86-3000, Heredia, Costa Rica.