OVSICORI-UNA reported that activity at Turrialba had declined overall since 27 May, though seismicity continued to be dominated by long-period earthquakes and small low-frequency volcanic earthquakes. A small explosion at 0516 on 1 June generated an ash plume that rose 300 m above the vent and, based on wind dispersion models, likely drifted NW. Some residents of Valle Central reported ashfall. Continuous spasmodic tremor that began at 2240 was associated with ash emissions that rose as high as 1 km and drifted N. At 0037 on 2 June an explosion was followed by high-amplitude spasmodic tremor and a dense ash-rich plume that rose 1 km and drifted NNW. Ash emissions continued; at 0520 and 0600 ash plumes rose as high as 2 km and drifted NW, N, and NE. Tremor amplitude decreased at 1240. Afternoon clouds prevented observations of ash emissions. Ashfall was reported in several neighborhoods in San José, including San Rafael de Moravia (31 km WSW), Sabana (38 km WSW), and in Limón, including Buenos Aires (17 km N), and Pococí (45 km N). During 2-3 June ash emissions were sometimes observed rising as high as 1 km and drifted N and NE. Ashfall in areas of Limón continued to be reported. Tremor amplitude began to decline at 0621 on 3 June, and then further declined to low levels at 0330 on 4 June. At dawn on 4 June plumes of water vapor and gas rose 500 m. Degassing and seismicity remained low through 7 June.

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)