Sicilian authorities have ordered the closure of the Macalube nature reserve after a 7-year-old girl was killed in an explosion of small mud crater.

Police said the girl, her brother and father were buried in mud and sediment when one of the craters exploded in western Sicily on Saturday. The 9-year-old boy was missing while the father was being treated at a hospital.

The unique phenomenon is the result of methane gas mixing with salt water and clay.

The director of the reserve, Mimmo Fontana, was quoted by ANSA as saying that a project to monitor the volcanic system had never been launched due to a lack of funding.