and the most recent active phase from 136,000 years to present. The most recent activity includes lava flows along with strombolian and phreatomagmatic explosions. Lava types include basalt and andesite erupted during different events suggesting the volcano is fed by two distinct magma chambers. Scientists believed that pulses of magma mixed together in the chamber before climbing upward—a process estimated to take several thousands of years. But Columbia University volcanologists found that the eruption of Costa Rica's Irazu volcano in 1963 was likely triggered by magma that took a nonstop route from the mantle over just a few months. Study authors called it the highway from hell. Eruptive history Irazú has erupted frequently in historical times — at least 23 times since its first historically recorded eruption in 1723. Its most famous eruption began in mid-March 1963, a few days before US President John F. Kennedy started a state visit to Costa Rica. It showered the capital San José and much of the central highlands of Costa Rica with ash. Eruptions continued for two years. Its historical eruptions generally have VEIs of 1 to 3. All historical eruptions have been explosive, and there have been many phreatic eruptions, and some have produced pyroclastic flows. The latest eruption lasted only 1 day, and occurred on December 8, 1994. It occurred at a flank vent and was a phreatic eruption, which produced lahars. Climate Gallery See also List of volcanoes in Costa Rica Irazú Volcano National Park References External links Costa Rican Vulcanologic and Seismologic Observatory: Irazú Virtual Reality Panorama of Volcán Irazú Costa Rica Volcanoes and Volcanics, USGS Parque Nacional Volcán Irazú (in Spanish) Subduction volcanoes Active volcanoes Stratovolcanoes of Costa Rica Mountains of Costa Rica Volcanic crater lakes Geography of Cartago Province Pleistocene stratovolcanoes Holocene stratovolcanoes