It has been almost exactly 14 years since the last eruptive period for Rincón de la Vieja in Costa Rica, but it looks like the volcano might be awakening from its break. Last Thursday (Feb. 22), the volcano experienced two small explosions in the early morning. Seismic records suggest the volcano also had small explosions on Feb. 19 and 20, according to the OVSICORI report for Feb. 25 (PDF). None of the explosions caused any damage to anything near the volcano and there are no reports of ash fall other than in the crater itself. These explosions are very similar in style to the September 2011explosions that were like phreatic in nature – that is, not new magma but superheated water generated the explosions. Of course, it is likely that new magma intruding the volcano is the heat source for the water, but these explosions could precede a new magmatic eruption by months or years (or lead to nothing at all). The volcano sits within a national park in Costa Rica and after these explosions, the National Emergency Commission has declared the crater area off-limits to visitors.
The last major eruption from Rincón de la Vieja was in 1966, when it produced at VEI 3 event that generated pyroclastic flows. All the way back in circa 1820 B.C., the volcano produced the Río Blanco tephra from a larger VEI 4 eruption. The summit of the volcano hosts a small crater lake (see above), which could potentially add to the initial explosivity of any eruption as the water interacts with erupting magma. There are also abundant mudpots and springs within the national park as well, attesting to the persistent geothermal activity in the area. This geothermal activity is the reason why the Costa Rican government is looking to build a 200 MW geothermal energy plant in the National Park as well.
Image: Rincón de la Vieja / Eliecer Duarte (OVSICORI-UNA)