Humongous landslides can cause humongous tsunami waves — and University of Hawaii scientists have found new evidence of such 1,000-foot waves in the Hawaiian Islands.

There have been at least 15 giant landslides in the Hawaiian Islands in the past 4 million years — one block of rock that slid of Oahu was the size of Manhattan, according to the U.S. Geological Survey. reports: 

Unlike tsunamis from earthquakes, the Hawaiian tsunamis strike when the island chain’s massive volcanoes collapse in humongous landslides. This happens about every 100,000 years, and is linked to climate change, said Gary McMurtry, a professor at the University of Hawaii in Honolulu.

Sitting about 30 feet (10 m) away from today’s Ka Le (South Point) seashore are boulders the size of cars. Some 250,000 years ago, a tsunami tossed the enormous rocks 820 feet (250 m) up the island’s slopes, said Fernando Marques, a professor at the University of Lisbon in Portugal. (The boulders are closer to the shore now because the main island of Hawaii is one of the world’s largest volcanoes, and its massive weight sends it sinking into the Earth at a rate of about 1 millimeter a year.)

McMurtry’s team found two younger and slightly smaller tsunami deposits at South Point on the main island of Hawaii, one 50,000 years old and one 13,000 years old. He suggests the tsunami source is the two Ka Le submarine landslides, from the flanks of the nearby Mauna Loa volcano. The waves carried corals and 3-foot (1 m) boulders 500 feet (150 m) inland.

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