The Marquesas Islands are volcanic in origin, overlying a mantle hotspot, with high mountain peaks and ridges. They lie in the path of the strong South Equatorial Current, flowing from the east, producing eroded coastlines, with steep cliffs dotted with sea caves. Coral reefs are limited to a few sheltered bays. The Marquesas lie farther from a continental landmass than any other island group on Earth. Despite this isolation, the islands suffered the effects of an earthquake in Alaska in 1946 when they were hit by the resultant tsunami, which rose up to 40 ft (12 m) high in some places.