SHELF LIFE
COURTESY OF USGS HAWAIIAN VOLCANO OBSERVATORY
ANATOMY OF A LAVA SHELF: 1. The lava bench at East Lae'apuki had reached a size of about 55 acres when this photo was taken Nov. 8 and remains about the same size now. 2. Steam is visible from where lava is entering the ocean through a tube system. 3. The white dots inland from the cliff are warning signs posted by rangers from Hawaii Volcanoes National Park. 4. The cliff marks older shoreline. CLICK FOR LARGE
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Collapse of massive lava shelf appears imminent
Newly formed volcanic land could collapse at any time
HILO » On the barren, wave-battered coast of Hawaii Volcanoes National Park, 55 acres of new lava land are poised to crumble into the sea with a roar.
This thin shelf of new land, known to geologists as a "bench" or "delta," is the largest piece of unstable ground ready to collapse into the ocean since current Kilauea eruptions began in 1983.
Built on sloping volcanic rubble, the bench could go more or less at once. That happened in the largest previous collapse on Nov. 28, 2005, when 44 acres crumbled into the ocean over 4 1/2 hours.
Hawaiian Volcano Observatory head Jim Kauahikaua said the bench could continue what it has done since it began rebuilding in 2005, cracking off just a few acres from time to time.
No one was injured in 2005, but collapses can be deadly. In April 1993, park visitor Prem Nagar disappeared when the small bench he stood on, just a half-acre, crumbled into the ocean.
COURTESY OF USGS HAWAIIAN VOLCANO OBSERVATORY
Lava flows over a former sea cliff adding to a new lava bench in the foreground in this Sept. 20 photo. The bench rests on unstable rubble on the sloping sea floor beneath it. CLICK FOR LARGE
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Up to 900 people per day visit the park coast, said park ranger Rob Eli. But no more than a few dozen make the arduous, three-mile hike from the end of Chain of Craters Road to the big bench at East Lae'apuki. "It's a difficult, long hike," taking as much as five hours for the round trip, Eli said.
About two miles beyond is the much smaller, four-acre East Ka'ili'ili bench.
Eli asks anyone heading off into the still cooling desert of recent lava flows, "What's your plan?"
COURTESY OF USGS HAWAIIAN VOLCANO OBSERVATORY
More than a year after 40 acres of land on the coast of Hawaii Volcanoes National Park tumbled into the sea on Nov. 28, 2005 lava flows have created a new "bench" of rock at the base of a 100-foot high sea cliff. The new bench could collapse soon. CLICK FOR LARGE
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It's a way of getting them to think about what they don't know. And one thing they don't know is how a bench is made.
Benches are built on sloping, underwater ground. Even Kauahikaua doesn't know how steep the slope is. "There is so little detailed information offshore," he said.
When 2,200-degree lava hits water, it makes an enormous amount of steam that tears the flow apart, making sand and rocks underwater, not the neat equivalent of a new paving job.
The more-or-less paved look takes place only after enough rubble is deposited in the sea that continuing flows reaching the bench remain above water. Underneath this shelf-like bench remains a jumble of geo-junk waiting for a geological excuse to destroy itself.
The hiker who hasn't been prepped with the "What's your plan?" question won't be saved by merely staying off the bench, on top of an older sea cliff. In 2005, the 44-acre collapse included 34 acres of bench plus 10 acres of former cliff.
On the advice of the volcano observatory, the national park now maintains a rope barrier 300 to 600 feet back from the old cliff.
In a big collapse, lava will gush, steam will blast, and boulders will fly in every direction, endangering anyone seaward of the rope barrier.
And then, unless the lava flow stops, the process starts over.
GRAPHICS BY DAVID SWANN
HOW A LAVA SHELF IS FORMED
1. Lava hitting the ocean "freezes," forming glass-like rubble underwater.
2. Lava flows build a "bench" on some of the loose rubble. Some flows mix with the rubble, but are fragile.
3. The rubble settles, creating cracks in the bench.
4. The rubble slides seaward while the bench above collapses. The sudden fresh flow of lava into the sea causes steam explosions.
5. A series of flows and collapses can make it impossible to tell the difference between old, safe ground and a new, unsafe bench.
6. Sometimes only part of a bench collapses, giving a false impression that land behind a cliff is safe.
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