Irazú Volcano

Irazú is an active stratovolcano in Costa Rica’s Central Volcanic Range. Its 1963–1965 eruption deposited ash across the Central Valley, including San José.

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Irazú eruption of 1963–1965: A prolonged Irazú eruption that began in March 1963 and sent ash over Costa Rica’s Central Valley. This eruption made Irazú a direct hazard to San José and surrounding communities.
Stratovolcano: A steep-sided volcano built from alternating layers of lava and fragmented volcanic material. Irazú’s layered cone and explosive activity fit this volcanic form.
Central Volcanic Range: A chain of volcanic peaks in central Costa Rica, including Irazú, Poás, and Turrialba. Irazú is one of the range’s prominent active volcanoes.
San José: The capital and largest city of Costa Rica, located in the Central Valley. Ash from Irazú’s 1963–1965 eruption reached the capital and disrupted daily life.
Irazú eruption of 1723: A documented Irazú eruption in 1723, described in colonial-era accounts. Its historical reports provide an earlier comparison for the volcano’s activity.
Phreatic eruption: A steam-driven volcanic explosion caused when groundwater or surface water is heated by magma or hot rock. Steam-driven explosions account for Irazú’s 1994 activity.
Turrialba Volcano: An active stratovolcano in Costa Rica’s Central Volcanic Range, east of Irazú. Its nearby eruptions provide a regional comparison for Irazú’s activity and hazards.
Central Valley of Costa Rica: A densely populated highland region in Costa Rica containing San José and several other major cities. The valley lies within reach of Irazú’s ashfall and other volcanic hazards.
Irazú eruption of 1994: A phreatic eruption at Irazú in December 1994, involving steam-driven explosions. It illustrates that activity continued after the major 1963–1965 eruption.
Volcanic ash: Fragments of volcanic rock and glass smaller than two millimeters, blasted into the air during eruptions. Ashfall was the most widespread impact of the 1963–1965 eruption.