OVSICORI-UNA reported significant seismic activity at Turrialba starting on 14 July. Low-frequency signals indicating fluid movement grew from an average of less than 200 events per day to over 600 events on 14 July, reaching a peak of activity with over 1,000 events on 15 July. Low-frequency tremor was detected during 18-19 July. Elevated seismicity remained at least through the report posting on 20 July. No morphological changes at the surface were observed.

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)