OVSICORI-UNA reported that frequent small explosions and sustained tremor with significant and variable amplitude continued to be recorded at Turrialba during 3-5 May. Ash plumes rose 500 m above West Crater and drifted NW and SE, though larger explosions generated ash plumes that rose as high as 1 km. During 6-7 May gas-and-water-vapor plumes rose 1 km. Tremor was characterized as having short duration and a moderate amplitude; for a period between 0530 and 1700 on 7 May tremor amplitude was high but then afterwards it drastically decreased and a significant number of discrete volcanic earthquakes were recorded. Small lahars descended drainages on the upper flanks, mainly in the Río Aquiares drainage. During 0200-0900 on 8 May small, frequent ash emissions, that rose no more than 500 m, were observed coincident with the detection of spasmodic tremor. Gas emissions rose 500 m above the crater at least until noon on 10 May. The amplitude of the volcanic tremor decreased and remained low.

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)