OVSICORI-UNA reported that periodic phreatic explosions at Rincón de la Vieja continued to be recorded by the seismic network and webcams during 26-29 May and 1-2 June. Some of the events were not visually confirmed by webcams because of weather conditions or darkness. On 26 May a minor amount of ash fell in areas to the NW including in Los Angeles of Quebrada Grande, and Liberia. A phreatic eruption at 1521 on 27 May generated a plume that rose 1.5 km above the crater rim. At 1524 on 28 May an event generated a plume that rose 3 km above the rim and drifted W. Phreatic eruptions at 1745 on 1 June, and at 1446 and 1701 on 2 June produced plumes that rose 1-2 km.

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)