A series of earthquakes and shifting ground on the slopes of Kilauea has scientists wondering what will happen next at one of the world’s most active volcanoes.

A lake of lava near the summit of Kilauea on Hawaii island had risen to a record-high level after a recent explosion. But in the past few days, the pool of molten rock began sinking, and the surface of the lava lake fell nearly 500 feet.

Meanwhile, a rash of earthquakes rattled the volcano with as many as 25 quakes per hour, and scientists’ tilt meters detected that the ground was deforming.

"Clearly the lava, by dropping out of sight, it has to be going somewhere," said Steven Brantley, deputy scientist in charge of Hawaiian Volcano Observatory, run by the U.S. Geological Survey.

One possibility is that a new lava eruption could break through the surface of the mountain, Brantley said.