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beamjockeyA novel way to celebrate the onset of New Year: Wetumpka, Alabama dropped an asteroid at midnight.
The "Asteroid Drop" commemorated the greatest natural disaster of Alabama history. Wetumpka sits on the rim of a large crater. Scientists say it's evidence of a meteor strike some 83 million years ago.
[...]
Of course, the citizens of Wetumpka have known about the crater since the discovery of the site in the late 1970's. But this was the first time the city came out to celebrate this particular part of it's history.
And what better place to do it than on the edge of the crater -- downtown Wetumpka.?
"A number of years ago, I was driving by here and thought, 'This street goes across. This street makes a T. The courthouse sits on a square like Times Square. Put a ball at the top and we'll have New Year's Eve.' So that's how it got started," Devenney said.
"Some Boy Scouts are going to flip the lights on the ground and light the ball. A couple of flares will go off on the ground. If everything goes well, it will look like real," explained co-organizer Donald Carey.
Saturday night's meteor impact was much more family-friendly than the first. Scientists estimate the energy released from the original impact was 175,000 times more powerful than a nuclear bomb.
The "Asteroid Drop" commemorated the greatest natural disaster of Alabama history. Wetumpka sits on the rim of a large crater. Scientists say it's evidence of a meteor strike some 83 million years ago.
[...]
Of course, the citizens of Wetumpka have known about the crater since the discovery of the site in the late 1970's. But this was the first time the city came out to celebrate this particular part of it's history.
And what better place to do it than on the edge of the crater -- downtown Wetumpka.?
"A number of years ago, I was driving by here and thought, 'This street goes across. This street makes a T. The courthouse sits on a square like Times Square. Put a ball at the top and we'll have New Year's Eve.' So that's how it got started," Devenney said.
"Some Boy Scouts are going to flip the lights on the ground and light the ball. A couple of flares will go off on the ground. If everything goes well, it will look like real," explained co-organizer Donald Carey.
Saturday night's meteor impact was much more family-friendly than the first. Scientists estimate the energy released from the original impact was 175,000 times more powerful than a nuclear bomb.
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no subject
Date: 2006-01-03 05:09 pm (UTC)no subject
Date: 2006-01-03 06:16 pm (UTC)no subject
Date: 2006-01-03 06:37 pm (UTC)Not a trace on the surface. It's a secret five-mile-wide cosmic impact crater. Which makes it even cooler.
beamjockey
Date: 2006-01-03 06:48 pm (UTC)City of the Big Shoulders Was Once City of the Big Hole
You probably don't worry much about getting hit by a meteor.
Small meteors are harmless. They burn away and vanish in friction with our atmosphere.
But big meteors are dangerous. They can blow craters in the landscape. They generate shockwave blasts capable of flattening buildings or trees for many miles. If they hit water, they can trigger tsunamis, or throw up enough dust and water vapor to create cloudy weather for days, weeks or months.
I was surprised to learn that this has already happened here. The Chicago area has already been hit by a devastating asteroid impact.
Of course, this was before I moved here. About 280 million years ago. (I did manage to experience the Blizzard of '79, though.)
The huge crater left behind, seven times the size of Arizona's famous Meteor Crater, gradually succumbed to erosion as wind and water wore away its walls. Much later, soil and rocks, brought by glaciers, were dumped atop Illinois when the glaciers receded. Every trace of the crater was buried.
In recent years, scientists have taken a strong interest in impacts of comets and asteroids upon the Earth. A really big collision can kick up enough dust, soot and water to change the climate for several years.
Such a disaster may explain the sudden demise of dinosaurs, and lots of other species, about 65 million years ago. That meteorite probably left a crater more than 100 miles wide.
Our local crater was much smaller than this -- about 5.5 miles in diameter. And much older; the first dinosaurs, not the last ones, were appearing on Earth at about the same time. Probably it had little effect on global climate. But it certainly made life in Illinois uncomfortable.
Some object from space, probably an asteroid, possibly a comet, slammed into the Earth at enormous speed. It landed in Des Plaines, where today Dempster Street crosses Interstate Highway 294.
Instantly, the energy of the impact vaporized much of the object and some of the surface. The explosion was the equivalent of nearly 4 billion tons of TNT. An expanding shockwave shattered rock in a wide circle around and below the target area.
Most of Des Plaines was flung into the sky, along with portions of Niles, Morton Grove, Park Ridge and Glenview in the east and Mount Prospect in the west.
Through the air, a pressure wave equivalent to winds of more than 150 mph would have flattened buildings in Milwaukee or South Bend, had there been any buildings there at the time.
After the initial shock passed, the crater floor rebounded, pushing older layers of rock more than 800 feet above their previous level, and tilting horizontal layers at large angles. This formed a central peak about a half-mile wide, similar to the uplifted peak you can see in some craters on the moon.
All the damage done in prehistoric times has been eradicated. On the surface, the place looks like any other piece of northern Illinois. How, then, did anyone discover the crater?
John McHone, a research geologist at Arizona State University, is currently using NASA's Sojourner robot to explore Mars. He took time out to answer my questions about the "Des Plaines Disturbance."
"It was first detected as a broad circular area of undependable water wells," McHone said. "Contract drillers could not predict rock layers nor water depths in this area, and would not accept fixed fees for sinking a water well."
(Continued)
no subject
Date: 2006-01-03 06:50 pm (UTC)In most of northeastern Illinois, rocks formed in prehistoric times lie in neat layers, one atop the other. Not underneath Des Plaines, Niles and Glenview. Here, rocks are fractured and jumbled. At the center of the region of rotten wells, the top layer is far older than the rocks in the surrounding region. Deep layers of sandstone had been lifted to a higher level.
"Elsewhere in the 5-to-5.5-mile-across disturbed area," said Michael Sargent, staff geologist and supervisor of the samples library of the Illinois State Geological Survey, "the rocks are uplifted in some parts and downdropped in others."
As wells were drilled, geologists gradually assembled a picture of the subsurface. In the 1950s, measurements of subtle variations in gravity indicated an area of unusually low-density rocks under the Disturbance. In 1962, ISGS geologists suggested that the Disturbance could be explained by an ancient meteor impact.
Convincing evidence came in the 1980s, according to Sargent, "in rock cores cut for the Metropolitan Water Reclamation District of Greater Chicago in their planning work for the Tunnel and Reservoir Project," more familiarly known as the Deep Tunnel.
McHone explained, "There is a system of very large tunnels underlying the greater Chicago area, designed specifically for flood control and water storage." In most places these tunnels were bored through deep rock, but in the Des Plaines area, they had to be dug through the much shallower layers of material deposited near the surface by glaciers. The rock is useless. "In fact, these rocks are so thoroughly fractured they will not safely allow tunnel construction."
Engineers drilled in many places to plan their tunnels. McHone (then at the University of Illinois), Sargent, and ISGS's W. John Nelson examined the minerals brought up in drill cores for evidence of impacts.
In the sudden violence of a cosmic impact, shockwaves bring materials to pressures and temperatures far higher than those created in merely terrestrial processes. It's possible to create mineral forms that are unique to this situation. Finding shock-created forms within a rock sample gives a geologist good reason to believe that the sample has experienced an impact.
In 1986, McHone, Sargent, and Nelson looked for "shatter cones," a conical pattern of fractures created by a passing shockwave. "A very crude analogy for a shatter cone," said McHone, "would be the little conical plug which pops out of a plate glass window when shot with a pellet rifle. True shatter cones are quite different and they can permeate brittle rocks subjected to the passage of a powerful shock wave."
It wasn't easy, because most of the jumbled rocks were too soft or too difficult to date. But the investigators managed to find a few of the brittle rocks they needed sandwiched between other, softer stones. And the brittle rocks held shatter cones. Their work changed the status of the Des Plaines Disturbance from "possible impact site" to "probable impact site."
It could happen again. The best guess is that an impact of this size happens, somewhere on Earth, about once every 250,000 years. So the chances that we'll get hit in the next year are small. But the potential damage is very large. A few astronomers have proposed making a search to map all threatening asteroids, but money is scarce.
Even the Chicago Fire doesn't hold a candle to the explosive cataclysm that created the Des Plaines Disturbance. Personally, I'm glad I missed it.
-30-
Re: Working on the edge
Date: 2006-01-03 07:05 pm (UTC)Yes, they found the shatter cones in samples from Deep Tunnel drilling.
As for Quatermass, if the buried Martian spaceship hasn't bothered us in 280 million years, it probably won't do so any time soon.