Scientists warn that a catastrophic “mega tsunami” could strike parts of the U.S. within our lifetimes, with the Cascadia subduction zone posing the greatest threat. This fault line runs from Northern California to Vancouver Island, and a major earthquake here could sink land by up to 6½ feet and generate a tsunami powerful enough to destroy entire coastal towns.

New research from Virginia Tech highlights that such land sinking would dramatically expand flood zones and delay recovery. Tina Dura, the study’s lead author, notes that these land changes could significantly slow down rebuilding efforts and increase risks for thousands living nearby.

The odds of a magnitude 8.0 or higher quake along Cascadia in the next 50 years stand at 15%—a sobering statistic. Alaska also faces tsunami threats from landslides and glacier melt, while volcanic collapses in Hawaii have produced enormous waves in the past, including a 1,000-foot wave that once hit Lanai.

These risks are all part of the Pacific Ring of Fire, one of the world’s most seismically active regions. The last major Cascadia quake occurred in 1700, meaning another is overdue. Experts stress preparation over panic: learn evacuation routes, sign up for emergency alerts, and have a plan—because it’s not a matter of if, but when.