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Report on Irazu (Costa Rica) — March 1994


Bulletin of the Global Volcanism Network, vol. 19, no. 3 (March 1994)
Managing Editor: Richard Wunderman.

Irazu (Costa Rica) Crater lake remains yellow-green, slightly acidic, warm, and high

Please cite this report as:

Global Volcanism Program, 1994. Report on Irazu (Costa Rica) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 19:3. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199403-345060


Costa Rica

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

All times are local (unless otherwise noted)

During March, yellow-green water in the crater lake at Irazú remained high, covering the bottom of the crater. Subaqueous fumaroles persisted in the N, NW, SW, and SE parts of the lake. At the contact between the slide deposit along the E crater wall and the lake, there appeared a new subaqueous fumarole. The lake temperature was 20-24.5°C, pH minimum was 5.5, and fumarole temperatures reached as high as 80°C.

Seismicity during 1993 took the form of sporadic, locally detected earthquakes with magnitudes in the 1.7-2.2 range. The earthquakes were thought to originate along a fault that lies within 5 km of the crater.

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: G. Soto, Guillermo E. Alvarado, and Francisco (Chico) Arias, ICE; E. Fernández, J. Barquero, R. Van der Laat, F. de Obaldia, T. Marino, V. Barboza, and R. Sáenz, OVSICORI.