The Volcán Turrialba has returned to normal emitting just steam and vapor, but experts who flew over the mountain Wednesday said they are concerned.
The national emergency commission set up the flight. Participating were Rolando Mora of the Universidad de Costa Rica in San Pedro and Geoffroy Avard of the Universidad Nacional in Heredia.
The volcanologists said that the volcano is undergoing change and that the surveillance of the mountain should be stepped up.
The Comisión Nacional de Prevención de Riesgos y Atención de Emergencias said that the emission of a tall column of ash and vapor Tuesday morning suggests something important is happening.
The commission said that experts are now studying the ash that was collected after the eruption. Ash fell as far west and north as Coronado and Guadalupe.
The character of the ash will say a lot about what is going on inside the mountain, said the commission. If the ash is from old deposits, the conclusion would be that the ash comes from the upper reaches of the two major vents and has been there awhile.
However, if the ash appears to be new and from the depths of the mountain, this may suggest that the mountain is moving to another, more active stage, said the commission.
So far, emergency officials have asked that workers not return to the farms close to the volcano. They said they are worried about the workers being affected by the gas.
The mountain has been erupting off and on for three years. The national park surrounding the volcano remains closed to visitors. Mora is with the Red Sismológica de la Universidad de Costa Rica, and Avard is with the Observatorio Vulcanológico y Sismológico at Universidad Nacional.
In addition to the overflight Wednesday, volcano experts were at the mountain Tuesday after the eruption was reported.
Scientists have been keeping a close eye on the mountain. There are sensors that register tremors showing internal movement of magma, and there even are automatic cameras that watch the crater.