On 25 September, scientists from OVSICORI-UNA reported results from three field trips to Turrialba to inspect new fissures and to assess the impact of gases on surrounding areas. Winds carrying toxic gases 10 km SW, to the S side of Irazú volcano, caused trees to exhibit mild burns to a greater degree than effects from the previous year. Vegetation within a 4-km-radius on the W, NW, and E flanks was also burned more severely that previously noted. Several elongated fissures in the rim S of the W crater were documented, as well as 1 km down slope NW of the crater. One E-W-trending crack that was first seen several months before had opened up as much as 12 cm, and emitted gas and vapor at 90 degrees Celsius. On the NW lower flanks, at least three radial fissures emitted high gas-and-vapor plumes. Some fissures near the summit were 5-10 cm wide. The last of the remaining settlers in the affected areas had moved away due to the intensification and impact of the gases.

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)