Some geologists consider an unstable rock face at Mount Breakenridge, above the north end of the giant fresh-water fjord of Harrison Lake in the Fraser Valley of southwestern British Columbia, Canada, to be unstable enough to collapse into the lake, generating a megatsunami that might destroy the town of Harrison Hot Springs (located at its south end).
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On May 18, 1980, the upper 460 meters (1,509 feet) of Mount St. Helens failed and detached in a massive landslide.
In his book 1421: The Year China Discovered the World, amateur historian Gavin Menzies argues that Zhou Man built a fortess at Bittangabee Bay Australia and that his fleet approached and mapped the Pacific coast of North America and may have been wiped out by a megatsunami resulting from a comet impact creating Mahuika crater.