The San Jose international airport was temporarily closed for security reasons because the volcanic ash could cause problems for planes, the civil aviation authority said.
Airport sources said eight approaching flights were diverted as the order was given, some to the north of the country and others to El Salvador.
Turrialba erupted twice on Monday, first at dawn and again just before noon. The second eruption sent an ash cloud 4,000 metres into the air.
The volcano stands 35 kilometres from the capital.