During last week the Rincón de la Vieja has had some small explosions that ejected ash in the area near the volcano. This is the first sign of activity of the volcano from a brief period in September 2014. No explosion was particularly important, with a small ash plume that rose less than a kilometer above the volcano.
Volcanologists from the OVSICORI oversight agency of the volcanoes of Costa Rica visited the Rincon de la Vieja to get a better view of the recent unrest. They found a number of small ash deposits linked to other steam explosions that have occurred since the beginning of 2016 (probably small enough to go unnoticed, especially if they were obscured by clouds).
The most interesting thing they found was that the ash from the explosions, even though most are pieces of rocks and pieces of pre-existing sulfur, contain a small part of what appears to be fresh lava in the form of small bursts of volcanic glass (obsidian). This suggests that there might be a magma body which is not hiding too far below the summit crater lake of the Rincón de la Vieja.
The lake in the summit crater emits more magmatic gases such as hydrogen sulfide and sulfur dioxide over the last few years and is also more warm (45-55ºC). Just like the glass in the ashes, these changes in the lake suggest to OVSICORI there could be magma nears the surface.
What is most important is the concern of the OVSICORI about these changes in the Rincón de la Vieja which could mean that the volcano entered in a more dangerous period, with potential for large explosions and production of lahars ( flows of volcanic mud) increasing. This means that people living near the volcano need to keep close attention to how the volcano behaves.
The last major eruption of the Rincón de la Vieja was an eruption of VEI 3 in 1966, even though it produces numerous small explosions in the half century since the eruption. In Costa Rica, Poas and the Turrialba were much more active in the last two years. The most famous volcano in Costa Rica, Arenal, was surprisingly quiet since 2010 after 32 years of almost continuous eruption.
March 22, 2016.Rincon De La Vieja , Costa Rica :
Source : COSTA RICA TIMES
Photos : rutaecoturista.com