Federal scientists say they've pinpointed the cause of tsunami waves that destroyed an Alaska village following the 1964 Great Alaska Earthquake, the second-largest ever recorded, at magnitude 9.2.

The U.S. Geological Survey says undersea landslides in water up to 1,150 feet deep triggered a tsunami that killed 23 people in the Prince William Sound village of Chenega (chen-EE'-gah).

That's far deeper than the underwater slides that sent deadly tsunami waves into the towns of Valdez (val-DEEZ), Seward and Whittier.

Undersea mapping shortly after the quake reached only about 330 feet, and the cause of the Chenega tsunami previously was a mystery. USGS researchers used multi-beam sonar and other tools to find evidence of deeper slide.

The deadly waves reached Chenega four minutes after the earthquake.