OVSICORI-UNA reported that the level of the water lake in Rincón de la Vieja’s summit crater declined during 30 May-21 June based on drone footage. A small phreatic eruption occurred at 0607 on 22 June. Several small phreatic eruptions were recorded overnight during 25-26 June. A small event at 0547 on 26 June produced a steam-and-gas plume that rose 1.5 km above the crater rim. Another small event at 0308 on 27 June produced a gas-and-steam plume that rose more than 1 km, though weather clouds and darkness obscured views. The Alert Level remained at 3 (the second highest level on a 0-4 scale).

Geological Summary. Rincón de la Vieja, the largest volcano in NW Costa Rica, is a remote volcanic complex in the Guanacaste Range. The volcano consists of an elongated, arcuate NW-SE-trending ridge 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. Activity has migrated to the SE, where the youngest-looking craters are located. The twin cone of Santa María volcano, the highest peak of the complex, is located at the eastern end of a smaller, 5-km-wide caldera and has a 500-m-wide 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 historical eruptions possibly dating back to the 16th century, have been from the prominent active crater containing a 500-m-wide acid lake located ENE of Von Seebach crater.

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