Sound Science Bite: May 13. A Big Wave You Don't Want to Catch

In the news lately are the fissure eruptions on the big island of Hawaii, but much less has been said about dangers that could result from giant landslides into the sea creating megatsunamis. First, let me say that there has been a certain amount of unnecessary verbal "sturm und drang" over this possibility in the social media. The fact is there have been 15 giant Hawaiian landslides over the past 4 million years, making an average of one every 270,000 years. On the other hand, they don't follow a schedule and one could occur tomorrow (but not likely). The last one occurred 100,000 years ago.

Computer simulations have indicated the tsunami wave height from such an event could be as high as several hundred meters (over 1000 feet) around Hawaii and up to 40 meters (over 100 feet) along the West Coast. Such rare but devastating events are termed "low frequency, high impact" – another example being the collision of the Earth with a large asteroid. Geological studies have shown such tsunamis have occurred in the past. The extreme height of these tsunami waves (there would be a series of waves of increasing height) makes evacuating to higher ground very difficult, and it is not clear even a tall reinforced building would be a safe haven. Only islanders in the mountains might survive in Hawaii as the waves would hit within minutes of the landslide. Even the 12 hour warning time for the West Coast would not be sufficient for evacuation to occur.

The current danger area is associated with the Kilauea volcano in the southern part of the big island. The submerged Hilina slump lies above a steep undersea slope south of the volcano. The current fissure activity could signal accelerating slumping, but scientists have little ability to forecast a landslide. Most of the landslide activity is much more frequent (about once per 100 years) than the catastrophic ones and rather minor by comparison. Nevertheless, the 1975 tsunami caused extensive damage and fatalities in Hawaii, but only minor damage in California. Geologists have called for more research, since should such an event occur it would kill millions of people and cause incalculable damage in Hawaii and around the Pacific rim.