OVSICORI-UNA reported that two eruptions were recorded at Rincón de la Vieja, at 2227 on 20 January and 0225 on 23 January, though weather conditions prevented visual confirmation of plumes. Each event was 1-2 minutes long. At 1139 on 25 January an eruption produced a plume that rose 500-1,000 m.

Geological Summary. Rincón de la Vieja is a volcanic complex in the Guanacaste Range of NW Costa Rica. Sometimes referred to as the Rincon de la Vieja-Santa María Volcanic Complex, it consists of a slightly arcuate 20-km-long ridge of 12 craters and pyroclastic cones constructed within the 15-km-wide early Pleistocene Guachipelín caldera, whose rim is exposed on the south side. Sometimes known as the "Colossus of Guanacaste," it has an estimated volume of 130 km3 and contains at least nine major eruptive centers. The Santa María cone, the highest peak of the complex, is located on the E side of the ridge and has a lake within the 400-m-diameter crater. A Plinian eruption producing the 0.25 km3 Río Blanca tephra about 3,500 years ago was the last major magmatic eruption. All subsequent eruptions, including numerous reported eruptions possibly dating back to the 16th century, have been from the active crater, near the center of the complex, with an acidic 300-m-diameter lake.

Source: Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional (OVSICORI-UNA)