OVSICORI-UNA reported that small phreatic events continued to be recorded at Rincón de la Vieja during 23-29 August. Four small events were recorded during 1900 om 24 August and 0828 on 25 August. The event at 0828 produced a steam-and-gas plume that rose 3 km above the crater rim and drifted NW. Four small events were also recorded during 27-28 August; the event at 0813 on 28 August lasted two minutes and generated a steam-and-gas plume that rose 2.5 km above the crater rim. The Alert Level remained at Level 3, Orange, the third level on a four-level 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)