OVSICORI-UNA reported that multiple eruptive events were recorded at Rincón de la Vieja on 5 January, though most of them were small. A notable explosion at 1833 ejected incandescent material above the crater rim that was visible in webcam images for about 30 seconds. Darkness obscured views of a plume and no ash was visible in satellite images. Residents reported hearing a loud explosion and sounds indicating active lahars; lahars in the Penjamo and Azufrado rivers reached residential areas within 50 minutes of the event. An eruptive event was recorded at 1858 on 10 January, though cloud cover prevented visual confirmation.

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)