April 25, 2008 -- Every 100,000 years or so, something gives way on the island of Hawaii, producing the largest landslides on Earth.
Aside from burying everything in their path, the landslides might also launch huge tsunamis that travel across the Pacific. Such mega-slides of the past are obvious to oceanographers mapping the undersea slopes of all the Hawaiian islands.
But with Hawaii's population tipping 1.3 million, not counting tourists, what of the next mega-landslide?
Researchers testing rocks from a core drilled more than 10,000 feet (1.9 miles) into the island of Hawaii think they see just the sort of weak rocks that could serve as a surface for a gigantic landslide. The rocks are loose, ground-up glass still being made today when lava flows from a volcano to the ocean, is quenched there, and then ground and churned by waves.
"Basically, we're looking at a pile of glass," said Donald DePaolo, director of the Center for Isotope Geochemistry at the University of California, Berkeley.
DePaolo worked on the Hawaii Scientific Drilling Project (HSDP), which bored a hole down into the volcano near Hilo to find out more about how the Hawaiian Islands were created.
The weakest layers of ground-up glass were found about two-thirds of a mile (3,520 feet) down, said geologist Nick Thompson of Bournemouth University in the U.K. Thompson is the lead author of a paper about the stability of the Hawaiian volcano's flanks, which appeared in the April issue of the Journal of Volcanology and Geothermal Research.
"They just fall apart in your hand," said Thompson of the core's weakest sections. "It's just like sand you find at the beach."
That sand poses a danger because it could be acting like a bunch of ball bearings under a large chunk of land that could give way under certain conditions. In fact, said Thompson, part of the island is already collapsing -- albeit as more of a slump than a slide.
"The whole south part of the island is a slump," said Thompson. An area called the Hilina Slump of the Kilauea volcano, in particular, could be on the way to becoming a faster-moving slide that spreads out onto the sea floor.
One thing that might cause the slump to slide is a drop in sea level, Thompson said.
Previous research has investigated whether the Hawaiian landslides coincide with global ice ages, when huge amounts of water become trapped in polar ice and sea level drops. If sea level drops below the sandy, unstable layer, that could make it even less stable and turn the slump into another great Hawaiian slide.
But that's a big 'if,' Thompson acknowledges. He and his colleagues still have to make the case for a full-fledged layer of that sandy stuff way down there which extends in all directions and creates a slide surface.
To do that will require drilling more holes.
The core from HSDP, however, was 25 years in the making and proved extremely difficult due to cultural issues and equipment problems, said DePaolo. So the current chances of more such probes into the Hawaiian past and future seem unlikely.
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Larry O'Hanlon's blog: Earth Impacts
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