Scientists are keeping a close eye on the Turrialba volcano because instruments are detecting small earthquakes and the possible movement of magma inside the mountain. So far the activity has not become visible in the craters, they said.
Since July 14, the Observatorio Vulcanológico y Sismológico de Costa Rica at Universidad Nacional said it has observed low-frequency sounds characteristic of movements of fluids. The number went from 200 a day to 1,000 at the peak July 15. That average seems to be continuing.
Since Thursday, the scientists have been detecting low-frequency tremors with a cumulative duration of 90 minutes by Friday.
The observatory has the mountain covered with sensors and a camera trained on the craters. Some kind of activity has been expected because Turrialba has been emitting gas and ash since 2010.