Arenal in Costa Rica, erupting in July 2007. Image courtesy of Arenal.net.
Arenal in Costa Rica is one of the most active volcanoes in Central America. It is almost one of the most picturesque (see above) and, dare I say, touristy, volcanoes in the world. However, even volcanoes that seem "benign" like Arenal require special precautions.
Yesterday Arenal has two small eruptions that were accompanied by unusual tremors, (in spanish) according to Javier Pacheco of the Volcanological and Seismological Observatory of Costa Rica (OVSICORI). The tremor started at 7 AM and continued until 4:30 PM, suggesting some movement of fluid or magma in the volcanic system under Arenal. These events, along with increased degassing noticed last week, prompted rangers at the national park surrounding Arenal to evacuate visitors from the park, however, at this time there is no indication at people living near the volcano will need to leave. The volcano currently sits at Alert Level 3 (of 4).
I had also reported a few weeks ago that Turrialba had been showing signs of new activity. Eliecer Duarte of OVSICORI had this to say on June 13th:
Augmented fumarolic activity has been observed 360 degrees around the external upper summit walls of the active west crater. Such degassing has been acompanied, over these recent 2 months, by widening of radial cracks (1.5 cms average), tall vertical gas and vapor plumes (1-2 kms tall), and one sustained discrete seismic swar (amounting hundreds of quakes a day). Cracks on the summit showed 94ºC while fumarolic vents, in the lower parts of the crater, show points with temperatures between 120 and 160ºC. During April-May deep burning of dairy pastures and forests reached as far as 3.5km (towards NW and W). Widespread corrosion increases as the rainy season progresses.
He interprets this new activity as a blockage in the crater bottom, thus promoting "degassing through upper walls". (You can read the whole report here, albeit the link is a PDF in spanish). However, there is no suggestion made that this might be leading to renewed magmatic (rather than hydrothermal) activity for Turrialba. In fact, reports of an ash eruption from Turrialba yesterday have been ruled as false (in spanish) according to Costa Rican officials (the same can be said for rumors of ash from Irazu [in spanish] as well). However, it definitely seems like a volcano to keep a close watch on for the next few months.