Right now, the U.S. Geological Survey is still trying to understand the new fissure. If the lava flow stabilizes, residents could return to unharmed homes in a week or two. But if the new fissure follows a pattern set by other fissures on Kilauea, then the evacuation could “last for a prolonged period of time,” says Klemetti.

And “because it tends to fall out of public view, it can have a long-term impact on the communities,” he says. It’s happened several times before.

Kilauea is “unlike a lot of volcanoes because it’s a shield volcano”—meaning it has long, sloping sides—“and because it’s huge,” Klemetti says. “The scale of it is hard to comprehend until you’re on the volcano and you realize you can drive 20 miles and still be on the volcano.”