OVSICORI-UNA reported that a small ash eruption at Turrialba began at 1153 on 23 October. An explosion at 1710 on 24 October produced an ash plume that rose 800 m above the crater and drifted SSW. Multiple explosive events occurred during 24-25 October; poor weather conditions sometimes prevented views of the activity. On 25 October 10-minute-long explosive events began at 0730 and 0927 and generated ash plumes that rose 1.5 km and 200 m, respectively; plumes drifted NW and W. Pyroclastic flows from collapsing ash columns were generated both times. Volcanologists conducting fieldwork on 26 October observed morphological changes at the S edge of the W crater and nearby areas due to the recent activity. They noted fresh light-colored ash and tephra deposits on the steep wall of the active crater. Three small explosions generated ash, steam, and gas emissions. Tephra was deposited as far as 400 m away in various directions from the crater.

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)