OVSICORI-UNA reported that a phreatic eruption from Turrialba that began on 5 January was preceded by a day of increased seismicity and about 30 minutes of almost constant tremor. Two events detected about 15 minutes apart were followed by reports of ashfall as far away as 30 km. Field observations on 6 January revealed that two small vents had opened and joined together on the SE inner wall of the SW crater. Gas emission temperatures were more than 350 degrees Celsius. On 8 January seismic activity and gas emissions decreased. Observations the next day revealed that the combined vent was about 25 m wide and 80 m long. Around 60 people had evacuated from nearby farms.

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)