He argues that Stearns' coral deposits might actually have been ancient trail markers built by native Hawaiians who used white coral to stand out against the black volcanic rock. But computer models are only as good as their input, Clague says, and the size, speed and direction of the landslides are still uncertain. Unfortunately, no one can go back to examine Stearns's site, because no one has been able to find it. Clague suspects island farmers dug it up to plant sugarcane. Whether the tsunami that hit Lanai was colossal or merely huge, waves of that size only come around every few hundred thousand years.
Most geologists agree that tsunami-causing landslides tend to start on active volcanoes.
Pressure builds up until magma is suddenly injected into a rift zone, a region of fissures and faults on the volcano slope. This triggers a massive earthquake which, when combined with the force of the magma itself, is enough to blast the side of the mountain away. If that's going to happen anywhere, it's on the Big Island, home of Hawaii's two active volcanoes Kilauea and Mauna Loa. Satellite measurements show Kilauea is on the move. The entire south side of the mountain is spreading seaward at the rate of 10 centimetres a year, and in 1975 a magnitude 7.2 earthquake shoved the flank 10 metres out and 3 metres down all at once.