OVSICORI-UNA reported that several eruptive events at Rincón de la Vieja were recorded during 22-26 March, though none were visible due to weather conditions. A one-minute-long event was recorded at 0350 on 22 March. A series of pulses occurred over a 20-minute period, at 0140, 0146, and 0159 on 23 March, with additional small events at 1045, 1339, 1939, and 2244. According to the Washington VAAC a possible ash emission was visible in satellite images at 1420 drifting W at an altitude of 2.7 km (9,000 ft) a.s.l. OVSICORI-UNA noted that a series of small eruptive events were recorded during 0129-0140 on 25 March. A small eruption with possible two separate pulses was recorded on 26 March.

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.

Sources: Observatorio Vulcanologico y Sismologico de Costa Rica-Universidad Nacional (OVSICORI-UNA), Washington Volcanic Ash Advisory Center (VAAC)