Thursday, November 6, 2008

Meteorite Blast Pattern

I am posting this interesting article on the famous Arizona meteorite crater that has been used as an example in just about every book on geology. What makes it interesting is the detailed description of the blast event as it has been reconstructed. We have little of the object actually buried in the crust. Rather we have a destruction and blast pattern largely released outside of the crater itself that distributed fine molten particle many miles in all directions.

This scenario finds comparables in India, the Sahara Desert and elsewhere that had been preciously been identified but lacked a credible explanation, unless you call up a prehistoric atomic war. The idea that even a nickel iron meteorite could largely vaporize seems unlikely but must be considered. I expect that the effect is related to mass and initial speed of impact with the atmosphere.

This was still a small meteorite compared to what is possible and what we never wish to experience. I often wonder if the major hot spots on Earth were all triggered by massive impacts that were able to penetrate the crust and even perhaps crack it. Iceland is my favorite since our explanation there is based on the idea of diverging crustal spreading that has caused the hot spot. What if it is the other way around? Not too likely, but proving one or the other is not easy.

Then we have the giant Volcanoes. What got them brewing up? A deep penetrating asteroid would work fine. Let us hope we never get to find out.

This returns me back to the extraordinary event of histories greatest bullseye, the meteorite strike that triggered the crustal shift of the Pleistocene nonconformity. That meteorite struck the North Pole from probably the same direction in the sky as the Arizona Meteorite, except that it was perhaps a hundred miles off center from the pole so as to impart its kinetic energy as completely as possible to the crust. A very minimal shift if any in direction off the solar plane would put it on target.

The blast itself was initially contained within the mile thick ice which was lofted ice and debris into the Ohio valley and the Carolinas. The heat blast scoured Eastern North America. All this is credible in light of this article describing the Arizona blast. As a first guess, I think that we are looking at an event about ten to fifty times more powerful that the 20 megatons attributed to the meteorite in Arizona. That suggests that the meteorite was a million ton baby.

That suggests that there exists somewhere a remnant of perhaps half that or even a lot less out in the Canadian Diamond fields. The problem of course is that is not really a lot of material. It is two days work in our largest copper mines. Our best hope is to find tracers on the ground and try to map an epicenter.

This also suggests that the resultant impact crater may be much smaller than expected. The ice was impacted by the blast front and its energy transmitted into the crust but a lot less violently than from a straight rock on crust impact. I am much more comfortable about the survivability of this event outside of Eastern North America.


The original article can be found at this web site with a several illustrations but no attribution.

Fifty thousand years ago a huge boulder crashed into the desert flatlands in what is now Arizona leaving behind a bowl-shaped hole 4,000 feet wide and 570 feet deep. A study published in the journal Science concludes the stone that came in from space that day was a nickel iron meteor 100 feet in diameter and weighing 60,000 tons, traveling at speed of almost 45,000 miles an hour.

The question is, what ever happened to it? For years people have searched for the main body of the meteor, but it has never been found. The largest piece ever located is the so called Holsinger Meteroite, below, found within the crater, and weighing 1440 pounds. That from an original 60,000 ton bolide.

The collision erupted with the force of a 20 megaton bomb and sprayed molten rock for miles around the crater, says Elisabetta Pierazzo, a researcher at the University of Arizona Lunar and Planetary Laboratory and co-author of the journal study on the impact.

Pierazzo and her co-authors, researchers from Rutgers University, the University of Rhode Island, the University of California, Berkeley, and the Australian National University in Canberra, used math models and chemical analysis of pieces of the space boulder to determine that about 85 percent of the meteor melted upon contact. Only the BACK 15 percent of the 100-foot space rock remained free from the melting process. Instead it broke into bits and ended up strewn all over a five mile radius in every direction from the center of the impact site, leaving what have now come to be called Canyon Diablo meteorites.
The melted portion turned into grain-size particles called spheroids that were spread even farther and wider. Only a small bit of the spheroids and bits of unmelted meteor have ever been found.

At the time of the impact animals such as mammoths, sloths, bison, and camels roamed leisurely amongst the rolling hills and woodlands, while giant twenty-foot-plus wingspan
Teratorns roamed the skys above the yet to be named Colorado Plateau where the meteor landed. But the meteorite that slammed into the ground that day 50,000 years ago instantly changed everything for miles around. Casualties resulting from vaporization, burial by the ejected bedrock, and from the destructive air blast moving outward and across the landscape would have been devastating. Winds approaching 2000 miles per hour would have rushed unhindered across the flat landscape for two to five miles beyond the center of the impact, with hurricane force winds substained as far away as twenty-four miles. Vegetation would have been completely destroyed for up to 900 square miles, with damage over an additional 400 square miles. Large animals as far away as three miles would have been killed flatout and those as far as fifteen miles away would have sustained crippling injuries. Vaporized iron would have filled the air and hunks of hot metal would have been falling from the sky in a five-mile plus radius. Then nothing.

Since the coming of man, hundreds, if not thousands of pieces of the meteor, ranging from a few grams to a couple hundred pounds, have been found and picked up from the so-called Canyon Diablo scatter field around the impact site. Up to this time no reliable estimate of the total overall weight found thus far, or for the estimated amount of remaining pieces, has been forthcomimg. Meteorite hunter
Dr. Harvey Harlow Nininger, a well-respected student of things-meteor, has estimated that about 30 tons of specimens had been collected. Workers have estimated that 8,000 tons of iron are contained in the fine grained material around the crater. This leaves about 55,000 tons to speculate about. Some of it remains buried as drilling in the crater for the main bolide has shown. Some of it remains in the form of specimens in area surrounding the crater. Until the area was closed to meteorite hunting recently, hunters with metal detectors were still finding significant pieces. However, as stated above by Pierazzo, et al, 85 percent, 51,000 tons, the vast majority of the impacting body creating the crater, vaporized. It instantly turned from a solid nickel and iron rock into a gas, creating a cloud of super heated vapor riding the crest of the 2000 mile per hour winds, only to cool and condensed and rain nickel and iron spheroids down upon hundereds of square miles in every direction. True, probably not as grandiose as a single, huge thirty ton boulder from space buried or sitting there, but that's where the answer to the "What Happened to the Meteorite?" question stands now.

References had been made of the crater by members of the indigenous population from very early on, even to the point of using pieces of the meteor for ceremonial and ritual purposes as cited below. The first written report pertaining to the crater was not made until about 1871 by a man named
Albert Franklin Banta, known then as Charley Franklin, who served as a scout and guide for the U.S. Army and worked for a short time at Bosque Redondo while the Navajos and Apaches were interned there following The Long Walk. However, indigenous population or discovered in 1871, the question not fully resolved even to this day is JUST when was the coming of man to the Arizona plain AND could humans been around to have actually observed the the meteor's impact? The prevailing thought is man showed up just about the time the ice sheets began retreating, somewhere in the 12,000 years ago range (Clovis Culture). The meteor impact has been dated at some 50,000 years back, so it would seem highly unlikely if one were to use the above impact date and human arrival date that anyone would have been around to observe the event. However, there has been some very credible evidence recently that seems to indicate humans did infact inhabit the area much earlier than previously thought.

In 1979 a small cave was discovered in a remote section of southern New Mexico that seemed to indicate it had been used as shelter by very early inhabitants. By 1989 it had been visited by archeologists and by 1990 excavations were being carried out at the site. It had even been given a name,
Pendejo Cave. There is some evidence of human modification of animal bones from among artifacts retreived from archeologic zones predating Clovis. The finds indicate manufacture of bone tools, ornaments, and marrowing. They come from well-defined and dated layers, ranging from circa 13,000 to 50,000 YBP (years before present).

Native Americans inhabiting the desert southwest in a more generally accepted timeframe, have for centuries made note of a variety of celestial events, from the Chaco Canyon
Sun Dagger solstice device to the petrograph recording of the super nova burst dated at 1054 AD. They have also have a tradition for treating meteors and their meteorite remnants with a certain degree of reverence.

The so-called Camp Verde and Bloody Basin meteorites are transported specimens from the Meteor Crater impact site. Both were carried some sixty to eighty miles southwest of the crater. The Camp Verde meteorite, which weighs over one-hundred and thirty pounds, was found on top of a mesa in the corner of an ancient dwelling. The meteorite had been wrapped in feather and cloth and placed on a stone alter.
The Bloody Basin meteorite, which weighs over twelve pounds, was found in connection to a burial site. In another example, roughly thirty-five miles to the west-northwest of the Meteor Crater impact site along old Route 66 is the little town of Winona. In 1928, about five miles northeast of Winona, near an ancient Sinagua Indian village called Elden Pueblo that had been inhabited from about 1070 to 1275 A.D., a fifty-three pound meteorite now called the Winona Meteorite was discovered carefully buried in a stone cist. The manner in which the meteorite was buried suggests that the pueblo builders most likely considered the meteorite a sacred object --- possibly after witnessing its fall. The meteorite was an egg-shaped mass when discovered. However, even though the Indians were apparently able to move it to the burial site, it fell to pieces upon removal.

With such a spectacular nature-altering event as the impact at Meteor Crater one would think any surviving human inhabitants of the region would surely have been moved to record it in some manner. As of yet no such recording has been forthcoming.

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