OVSICORI reported that from mid-June through 8 August, several changes occurred at Turrialba, including opened fractures, spreading fumaroles, and an acute impact of gases on vegetation. Wide spreading of fumaroles on the upper edifice correlated with enhanced seismicity in mid-July. The principle fumarole in the bottom of the W crater reached 138 degrees C and produced a distinctive sound of a "high pressure valve" heard as far as 500 m away. The fumarole melted observable amounts of sulfur, a phenomenon not seen by the OVSICORI team in 25 years of continuous monitoring.

Multiple cracks associated with the expansion of the fumarolic areas around crater W were noted. A wide fumarolic field resided between two cracks about 100 m in length that propagated radially from the W and NW crater edges. Vegetation on the NW, W, and SW flanks appeared yellowish and dark brown, and patches of forest burned. Effects from the gases were observed in commercial farming areas.

Geological Summary. Turrialba, the easternmost of Costa Rica's Holocene volcanoes, is a large vegetated basaltic-to-dacitic stratovolcano located across a broad saddle NE of Irazú volcano overlooking the city of Cartago. The massive edifice covers an area of 500 km2. Three well-defined craters occur at the upper SW end of a broad 800 x 2200 m summit depression that is breached to the NE. Most activity originated from the summit vent complex, but two pyroclastic cones are located on the SW flank. Five major explosive eruptions have occurred during the past 3500 years. A series of explosive eruptions during the 19th century were sometimes accompanied by pyroclastic flows. Fumarolic activity continues at the central and SW summit craters.

Source: Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional (OVSICORI-UNA)