How do landslides cause tsunamis?

Tsunamis are large, potentially deadly and destructive sea waves, most of which are formed as a result of submarine earthquakes. They can also result from the eruption or collapse of island or coastal volcanoes and from giant landslides on marine margins. These landslides, in turn, are often triggered by earthquakes. Tsunamis can be generated on impact as a rapidly moving landslide mass enters the water or as water displaces behind and ahead of a rapidly moving underwater landslide. 

Research in the Canary Islands (off the northwestern coast of Africa) concludes that there have been at least five massive volcano landslides that occurred in the past, and that similar large events might occur in the future. Giant landslides in the Canary Islands could potentially generate large tsunami waves at both close and very great distances, and could potentially devastate large areas of coastal land as far away as the eastern seaboard of North America.

Rock falls and rock avalanches in coastal inlets, such as those that have occurred in the past at Tidal Inlet in Alaska's Glacier Bay National Park, have the potential to cause regional tsunamis that pose a hazard to coastal ecosystems and human settlements. On July 9, 1958, a magnitude 7.9 earthquake on the Fairweather Fault triggered a rock avalanche at the head of Lituya Bay, Alaska. The landslide generated a wave that ran up 524 meters (1,719 feet) on the opposite shore and sent a 30-meter-high wave through Lituya Bay, sinking two fishing boats and killing two people.

Learn more: Tsunamis and Tsunami Hazards