No. 37: Jan-Feb 1985
On the Hawaiian island of Lanai, limestone-bearing gravel blankets the coastal slopes. Called the Hulopoe Gravel, it now reaches a height of 326 meters above sea level. Taking into account the 1000,000-year age of the gravel and the slow subsidence of the Hawaiian Islands, the deposit probably reached 380 meters when it was first formed.
The big question is how it got deposited at such great heights. Highsea stands are rejected by the authors in favor of a single episode of catastrophic waves about 100,000 years ago. Earthquake-generated tidal waves are considered unlikely because of the great heights involved. (The highest tsunami ever recorded in historical times reach ed only 17 meters above sea level.) A great meteor impact or submarine volcanic explosion are good possibilities, but the authors favor a giant submarine landslide on the Hawaiian Ridge, noting that in 1958 a similar event off Alaska produced a wave that reached 524 meters above sea level.
(Moore, James G., and Moore, George W.; "Deposit from a Giant Wave on the Island of Lanai, Hawaii, Science, 226:1312, 1984.)