Report on Irazu (Costa Rica) — December 1993
Bulletin of the Global Volcanism Network, vol. 18, no. 12 (December 1993)
Managing Editor: Edward Venzke.
Irazu (Costa Rica) Crater lake rises 20 cm
Please cite this report as:
Global Volcanism Program, 1993. Report on Irazu (Costa Rica) (Venzke, E., ed.). Bulletin of the Global Volcanism Network, 18:12. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199312-345060
9.979°N, 83.852°W; summit elev. 3436 m
All times are local (unless otherwise noted)
During November, greenish-turquoise water in the crater lake at Irazú rose 20 cm and supported subaqueous fumaroles in the N and SE. Summaries of the behavior of the crater lake, including chemical data that suggests similarities to other quiescent volcanic systems, appeared in earlier reports (18:1 and 5).
Irazú inflated at a rapid rate in 1991, but it has only deformed a limited amount since then (18:1 and 3). For November the network of dry-tilt meters measured insignificant change. Seismicity was unreported in October and November, but when reported in 1993 it was generally at low levels.
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: E. Fernández, J. Barquero, R. Van der Laat, F. de Obaldia, T. Marino, V. Barboza, and R. Sáenz, OVSICORI.