The northern section of the Big Island (Hawaii) was formed by Kohala Volcano. The resistant cliff walls were cut by a deep canyon that today is known as Waipi'o Valley. The valley, carved by stream erosion, was once much deeper than at present. It was filled with water when the sea level rose at the end of the most recent ice age. Streams and landslides poured mud, sand, and gravel from the weathered lava cliffs into the submerged part of the valley, partially filling it and creating the flat valley floor. When the sea retreated, the early Hawaiians cultivated this fertile valley floor. The little flat area at the base of the sea cliff (extreme right in photo) is the debris from a large rockfall that occurred at the time of the April 3, 1868, earthquake. Occasional rockfalls and relentless waves keep the sea cliffs steep. Because of its shape and location on the north coast of the Big Island, Waipi'o Valley is especially vulnerable to tsunamis. The April 1, 1946, tsunami crested at 12.2 m (40 ft) at this location, and inundated the valley 805 m (half a mile) inland.

Image Credit: John Lockridge.