OVSICORI-UNA reported that periodic phreatic explosions at Rincón de la Vieja continued to be recorded by the seismic network and webcams during 13-19 May. Some of the events were not visually confirmed by webcams because of weather conditions or darkness. Two events, at 0524 and 0704 on 14 May produced steam plumes that rose 500 m above the crater rim. A few events were recorded the next morning. At 1127 on 15 May an event was characterized by local residents as a gas-and-steam plume rising 1 km above the crater rim and a gray, sediment-laden plume rising 400 m. Events at 0604, 0644, 0819, and 0825 on 17 May produced steam plumes that rose 500 m above the rim.

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)