Sunday, July 1, 2018

Kahului Underwater

"Such as slippage has not occurred for 100,000 years, but it has happened some 15 times in the geological record of Hawaii."
 
Imagine just for a moment an event that may or may not happen in human history. Imagine it happening today.

There are at least 15 giant landslides toppling into the Pacific from the Hawaiian Islands in the past 4 million years, with the most recent happening 100,000 years ago, according to the U.S. Geological Survey. One block of rock that slid off Oahu was the size of Manhattan.

The South Coast of the Big Island where Kilauea Volcano is active has a brittle lava shelf perched above the ocean, but not the size of Manhattan. More like Santa Catalina, California, or Cortes Island, British Columbia. Still, big enough to ricochet a 1000-foot wall of water around the Hawaiian islands. If the tumble causes large offshore earthquakes there could be trailing waves. The shadows of the islands themselves and its sheltering bays would likely spare Honolulu, but the Big Island and nearby Maui could be devastated.

What are the chances? The ongoing 2018 eruption began along a knife-like surface fault from Leilani Estates to Kapoho on the ocean. That knife’s edge is where lava from deep down reaches the surface in scores of outcrops, some now forming cinder cones. Between that edge and the sea is the older shelf at risk of slipping— about 75 square miles of heavy basalt. 

Such a slippage has not occurred for 100,000 years, but it has happened some 15 times in the geological record of Hawaii.
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 good news is that Hawaii doesn’t have to fret about a Fukushima-like disaster. Hawaii, along with Rhode Island and Vermont, passed laws that say no nuclear plant shall be constructed nor radioactive material accepted without the prior approval by a two-thirds vote in each house of the legislature. Hawaii has no nukes, including university research reactors.

Another piece of good news is that while landslide tsunamis may have a devastating local effect, they lose their power in the open ocean and don’t destroy distant coastlines like earthquake tsunamis. San Diego, Long Beach and Santa Monica can now exhale. That said, it might be a good idea to postpone that Hawaiian cruise ship excursion you were planning until after Kilauea’s eruption subsides.

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3 comments:

Robert Gillett said...

Pearl Harbor Naval Station has a number of nuclear-powered submarines and the occasional aircraft carrier. A beached submarine would not be able to keep its reactor cool if the ship were keeled over. I've never heard of a warship being beached by a tsunami, but it's not hard to imagine.

Joe said...

I understood that very large landslides could in fact generate ocean wide impacts. The Canary Islands mega-tsunami would be an example. https://www.youtube.com/watch?v=Zb4T8a1K5tw

Joe said...

The last three of my comments have never appeared. If comments are disabled, or if my comments are being moderated out, please let me know. Mahalo, Joe.

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