On 6 May, scientists from OVSICORI declared a Low Alert Level for Turrialba based on rapid changes during the previous three months, and intensified their fieldwork and data collection efforts. During aerial observation in February 2007, trees looked yellowish due to sustained gas emissions from the W crater. Vegetation growth was noted in previously burned areas on the W and SW flanks near the summit. On 21 April, a hot area (40° C) was noted 1.5 km SW of the summit, at the base of the volcanic edifice, that coincides with the WSW-ENE-trending Ariete fault. On 2 May, two larger hot and fuming spots were documented along the same fault, about 200 m SW of the first area. The vapor plumes were spotted from several kilometers away, above the forest canopy. Heat destroyed vegetation in an approximately 300 square m area along the S fault's plane.

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)