Communities along a 700-mile stretch of Alaska’s southern coast ordered their residents to higher ground after a powerful earthquake, but officials quickly downgraded and then canceled a tsunami warning in the area.

Tsunamis are a series of long waves caused by a large and sudden displacement of water in the ocean, usually from a large earthquake on or below the ocean floor. Tsunamis radiate in all directions from the epicenter and can cause dangerous coastal flooding and powerful currents that can last for hours or days.