© West Hawaii Today
Black dashed lines delineate 17 distinct landslides that have occurred around the Hawaiian Islands over the last several million years. The largest slides originated from the north sides of Oahu and Molokai. Colors ranging from pink to purple indicate the water depth around the islands, while shades of gray show land topography above sea level. Red areas on the Island of Hawaii indicate lava flows erupted within the past 200 years.
Black dashed lines delineate 17 distinct landslides that have occurred around the Hawaiian Islands over the last several million years. The largest slides originated from the north sides of Oahu and Molokai. Colors ranging from pink to purple indicate the water depth around the islands, while shades of gray show land topography above sea level. Red areas on the Island of Hawaii indicate lava flows erupted within the past 200 years.
In 1964, irregular submarine topography north of Oahu and Molokai was identified in newly available maps of the sea floor made by the U.S. Navy. James Moore, then Scientist-in-Charge at the USGS Hawaiian Volcano Observatory, suggested that this odd bathymetry might reflect massive landslides originating from those islands.
Moore's interpretation was disputed for more than 20 years until comprehensive mapping of the sea floor around the entire state of Hawaii was completed in the late 1980s. It turned out that Moore was right. Large - even catastrophic - submarine landslide structures litter the sea floor around the Hawaiian Islands. In fact, 17 major landslides have been identified off the shores of the main Hawaiian Islands. Fortunately, these slides are exceedingly rare - occurring, on average, only once every 350,000 years.
The largest landslides constitute significant portions of the islands from which they originated. Imagine if 10 percent of one of the islands suddenly collapsed into the ocean. Such an event would displace a huge amount of water and cause a large tsunami. Deposits of coral and sand have been found approximately 1,000 feet above sea level on several of the Hawaiian Islands. Catastrophic landslides are believed to have generated gigantic tsunami waves that washed ashore and left these deposits behind.
