That raises the risk for an explosion at the summit. Normally, when the lava lake level is high, temperatures are so hot that the groundwater in surrounding rocks is kept away from the magma. But as the lava lake levels fall below the groundwater table, water can start interacting with the magma, heating it up and creating steam, said USGS scientist Donald Swanson.

Source: Los Angeles Times May 09, 2018 17:04 UTC