The Altiplano in Bolivia. Lake Titicaca is at the top
Posted on 12/05/2003 6:43:33 PM PST by Mike Darancette
In 1989, Edward Bryant climbed a point on the southeast coast of his native Australia with a colleague and found an odd jumble of boulders well above the surf. A big wave, he thought, maybe a tsunami from an earthquake, must have tossed them up there. Over the next few years, however, the University of Wollongong geologist explored hundreds of miles of coast and found more signs of wave action, hundreds of feet above the water--too high for any quake-spawned surge.
An astonishing hypothesis of devastation from outer space formed in his mind. It gathered some praise, along with many ferocious brickbats from doubting colleagues. But what may be a geologic smoking gun has now turned up in 1,000 feet of water just south of New Zealand. Columbia University geologist Dallas Abbott has found what appears to be an impact crater 13 miles across, implying that something enormous, maybe half a mile wide, smashed into the crust there.
If further research confirms that the circular depression is a recent crater, it would lend dramatic ammunition to Bryant's controversial scenario: Five hundred years ago or so, as Europe was beginning its colonial explorations, a comet or perhaps an asteroid plunged to Earth seaward of Australia's New South Wales coast. It would have sent mega-tsunamis ripping into nearby islands and Australia, where Bryant has found not just rocks but trees and beach sand hurled far up bluffs and cliffs, along with whirlpool-carved cavities as much as 150 feet across--testimony, he says, to the sea's onslaught. At one place, Jervis Bay, waves apparently surmounted a headland 420 feet high. "Only a bolide could do this," says Bryant, using a technical term for a sky-bursting cosmic missile. Geologists know such things can happen--a much bigger impact is believed to have ended the reign of the dinosaurs--but no such catastrophe is known in recorded history.
People would notice something like that. Sure enough, Bryant found recorded tales from Australian aborigines and New Zealand's Maori people recounting how, not long before the arrival of Europeans, the sky heaved and split, stars fell, and immense floods swept the land. Aborigine tales told of a huge, disintegrating ball of blue fire shooting overhead. Around 1500, Maori people on New Zealand's South Island abandoned the seashore and moved inland. Huge impact-generated waves, Bryant thinks, may have destroyed not only their villages but also beds of shellfish that provided food. "It all added up," he says. "Something big hit the Earth, near here."
In 2001, he published a textbook, Tsunami--The Underrated Hazard, including his circumstantial tale of a missile from space. Some colleagues liked his daring conjecture. "It's a big idea, and it deserves attention," says Victor Baker, a planetary sciences professor at the University of Arizona who has visited Bryant's tsunami sites and believes the signs of gargantuan waves are legitimate. Something has to account for them, he says, "whether or not it is an object into the sea." Others are deeply skeptical of Bryant's evidence and impact scenario.
New Zealand geologist James Goff, a former government researcher, calls Bryant a usually excellent scientist who has "gotten religion" on mega-tsunamis. In a paper just out in the Journal of the Royal Society of New Zealand, he rips Bryant's thesis apart. Goff for years has honed the idea that tsunamis did indeed sweep much of his island nation around 1500, driving the Maori inland. But he says the waves were of the more ordinary sort that earthquakes generate, a few tens of feet high at most, not what he calls Bryant's "mega-tsunami from hell." He says Bryant has joined events that may have happened centuries apart and mistranslated Maori place names to stress a link with fire and celestial destruction--taking the Maori syllable Ka to mean fire, for example, when Goff says fever is a better meaning.
But Goff wrote his critique before last month's Geological Society of America meeting in Seattle, where Abbott reported her discovery. Early this year, intrigued by Bryant's book, she had pored over topographic maps of the seafloor in the region and found an apparent impact scar on the edge of the continental shelf just south of New Zealand.
When Abbott checked samples that oceanographic expeditions had scooped from the area, she found shattered minerals typical of meteor impacts. A field of tektites--globules of rock that melted and cooled in midair--spreads to the southeast of the crater just as it should from a impacter striking at a low angle from the northwest, the direction Bryant infers from the Australian tales. The crater, which Abbott calls Mahuika after a Maori fire deity, lies in a spot that would send waves against Australia at just the angle Bryant had already calculated. "It's young, almost surely less than a thousand years," she says, judging from the near absence of the sediment that normally builds up on the ocean floor.
"This is pretty exciting if the story holds up," says Steven Ward, a geophysicist at the University of California-Santa Cruz, who has a keen interest in comet and asteroid impacts. Goff agrees, but with neither a firm date for the crater nor sure evidence that cataclysmic waves hit New Zealand at the same time as it was formed, "the jury is still out," he says. Abbott hopes to settle the issue by gathering and dating samples of debris. An impact would have scattered material for hundreds of miles, creating a distinctive layer in the New Zealand soil, says Ward.
But even if a giant rock did plunge into the sea 500 years ago, it may not be enough to explain Bryant's catalog of devastation. Ward calculated that an object that leaves a 13-mile-wide crater off New Zealand might send waves washing 100 feet up the Australian coast 1,000 miles away, but not a cliff-scaling 400 feet. Bryant, however, has no doubts. "I don't like to believe it, but we had something mighty big hit out there."
Copyright © 2003 U.S. News & World Report, L.P.
You mean back in c. 1504 A.D.? This isn't to say there wasn't, only that it must have been a pretty localized "major disater".
Reading this I was reminded of Eugene Shoemaker, who I understand also received a lot of grief for his early work on earth impacts.
They found one crater, it's not uncommon for these things to come in swarms. Look for more craters.
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The Altiplano in Bolivia. Lake Titicaca is at the top
Little Ice Age 1350AD - 1850AD. Asteroid/comet impacts into water create a warm and wet climate. Impacts on land create a cold and dry climate.
...and it is very, very old. (humans were not around then)
Just as an impact on land can hurl ejecta for many miles, a large body landing in 1000 ft of water would eject huge volumes of water into the air in all directions. This enormous mass of water would crash back to earth some distance from the impact site, and may greatly amplify the tsunami that propagates along the surface.
In addition, the crater is on the edge of the continental shelf, and it may have caused a large underwater landslide which would also increase the strength of the tsunami.
Here is a map of the area. Notice the underwater shelf (southwest of the South Island) that drops off dramatically toward Australia to the northwest.
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