The comet of the holocene

A few tips for locating impact sites

What you need to realize is that first of all is most of the scariest ones don't make a crater at all.

Next leave your old understanding of geology and landform creation at the door. Keep all the hard data; lab tests, specimens etc. But keep in mind that untill SL-9 came along the only place a deep impact asteroid, or exploding comet had in the minds of the worlds brightest geophysical scientists was under the catagories of religious myth, science fiction, or legend. none of them were taking impacts seriously. So their interpretations of their data is therefore biased and suspect. Since they haven't been looking they're not gonna be very helpful. If you are looking for Rudolph's footprints in the snow, then someone who doesn't believe in Santa Clause probably won't be much help.

We're gonna come at this from the other side of the paradigm shift. Instead of looking at a location and trying to prove that it is impact related. We'll acknowledge that the earth must get hit more often than the moon. And that there is therfore no place on earth that isn't impact related to one degree or another. It's only a question of which impact, how hard, and when.

On the moon an impact structure takes a fractal form. It's almost allways a perfect circle. And a crater looks the same five feet wide, five miles, or five hundred. Impact structures here also take fractal forms that look the same at any scale But here impact structures only make a perfect circle if it's a really dense bolide comming in at a steep angle. The rest do something different. There's more than one form. And all of them leave a mark that is almost impossible to erase completely.

We'll start with the easy ones one the ocean floor. But first, imagine if you will, a large mudpie.(You can do it for real if you like but a thought experiment will get you there without the mess) Make it a big one, five feet wide or so. you want it wet and sticky with just enough aggregate to make it a little chunky. Then toss a rock so that it hit's the mud at about a 40 degree angle. Now look carefully at the result. you should see the point of impact and pointing away from the direction of impact, a splash curtain. For want of a better word and for the sake of simplicity I'll just call it an Impact Splash. that signature shape is just one of the Earths more common impact structures. 8 inches wide in a mudpie, or 80 miles wide on the ocean floor it still looks the same.
Turn on Google earth again and let's go back to the ocean floor. Look to the west of the Hawaiian Islands zoom out to about 1500 miles eye hieght you'll see a few places that look just like a rock plop in a mud pie. The word that comes to mind is simply "splat" There they are. Look around. They're all over the place. Happy hunting.

If folks are interested I'll point out some of the others as well.

Dennis
 
Thanks, I'm waiting for your comments. When I used that site and looked at the region in various modes (satellite, terrain, relief, etc.) the arc pattern also showed up on the relief map, but the area creating the arc is at lower elevation than the surrounding areas. Does this make sense to you?

Would the event you are positing leave a depression in the arc? To my untrained mind, it seems like it would be sort of like the edge of a crater, at least with some elevation in the arc area followed by lower elevations in one or both directions (in and out).
 
Re: A few tips for locating impact sites

My sister brought my attention to a mistake that might be slowing some folks down a bit. Google has two different products that some might confuse as being the same thing. so let's clear it up. The slow poke is Google maps. It's a web based application that's ok if you're looking for directions to Granny's house. Or if you already know the location of something. But it's too slow and cumbersome even with the best connection for our purposes. The other is Google Earth which is a free, stand alone program that, once installed, will do a nice job no matter what your connection speed. So he's a link:

http://earth.google.com/download-earth.html

While I'm here I'll point out another kind of impact structure.

In central California, just to the southest of Fresno is an ancient volcanic plug. It's an interesting place to study. Most basalt here in Cal. very dark, reddish nearly black. And that plug is some of the hardest in the country. It's a semi arid place and the wind and rain just go around. Not much erosion at all. So where you see a smooth surface. The wind and rain didn't do that. It's been peened smooth over the ages by countless small impacts. Once an impact has pulverized some of the surface the elements clear the debris fairly quick. And the more recent impacts are a lot lighter, and smoother than the surrounding rock. Let's take a look at one of those hit's at:

36deg. 42' 05.08"N
119deg 25' 06.63"W

You see it as an teardrop depression in the rock about 150' by 200' with a crack running down the center of the long axis. The cracks in the rock tell a story if you get some distance. You can see the crystaline structure of the basalt that formed as it cooled. Those are the native fractures. And then superimposed over that you can find the impact fractures. They'll be seen as places where a set of cracks converge on a central point that's progressively more broken up as you move to the center.

The thing to keep mind here is the fact that we're loking at an area that's only a mile or so on a side where we can identify hundreds of small impacts. Some of them fairly recent. And yet not a single crater.

If you are serious about looking for impact sites follow the cracks in the rock. Since erosion tends to be guided by fractures and weakness in the bedrock, and since the pattern of fractures created by an impact shock wave is a fractal form that looks the same all the way from a bb peck in a windsield up to something miles wide. Errosion can't erase an impact, it can only burry it. Take a look at Yosemite Valley. Look closely at the "apron" under glacier point. Think of it as a fracture cone like what you might see on the opposite side of that bb peck. Then zoom out and get a little distance. The native fractures in the granite are the long straight parralell, sometimes diagonaly crisscrossing cracks that run for miles. And, again the impact fractures are superimposed over the native cracks. Can you see it? Millions of years ago, before those mountains were uplifted by tectonic forces, before the glaciers removed all of the overburden, and carved out the valleys, and the age of the dinosaurs was still young, that would have looked like Barringer crater. only it was ten miles wide.

Take your time. Explore a little bit. See what you can find.
Dennis
 
Re: A few tips for locating impact sites

P.S. The geologists who's reseach made them conclude that the dome structures in the Sierra Nevada are a prduct of forces acting slowly from underneith did not believe that a deep impact could possibly have a significant role in landform creation anywhere. As I said; we're comming at this from the other side of the paradigm shift.
 
MrGullible said:
Thanks, I'm waiting for your comments. When I used that site and looked at the region in various modes (satellite, terrain, relief, etc.) the arc pattern also showed up on the relief map, but the area creating the arc is at lower elevation than the surrounding areas. Does this make sense to you?

Would the event you are positing leave a depression in the arc? To my untrained mind, it seems like it would be sort of like the edge of a crater, at least with some elevation in the arc area followed by lower elevations in one or both directions (in and out).
Click to expand...

The ring structures surrounding the comet explosion site weren't produced by the cratering of a solid impact. But by the compression waves of tremendous above ground, or at ground level, explosions. Here's a video from you tube of the PEPCON explosion a few years back.
http://www.youtube.com/watch?v=HJVOUgCm5Jk

of interest here is the compression wave expanding outwards from the blast. Imagine PEPCON, but a million times more powerful. Although I'll be the first to concede the a million might be a bit conservative.
 
jusdenny said:
The ring structures surrounding the comet explosion site weren't produced by the cratering of a solid impact. But by the compression waves of tremendous above ground, or at ground level, explosions.
Click to expand...

I know what you are positing, but where (other sources, science, other sites) are other examples of compression (or longitudinal) waves leaving the kind of evidence I'm pointing out from the relief map of Alabama, i.e. lower elevation? Thanks.
 
One more thing an I'll go away for a while. The farmlands in that ring structure have been settled and farmed since the first settlers. Because the bedrock is broken to smithereans. And therefore it has good drainage, and the water table was close enough to the surface that a well could be dug by hand. When you're looking for a place to settle in a build a farm for yourself, and all you've got for tools are a strong back, maybe a pick and shovel, and a couple of mules. It doesn't get any better than that.
 
MrGullible said:
jusdenny said:
The ring structures surrounding the comet explosion site weren't produced by the cratering of a solid impact. But by the compression waves of tremendous above ground, or at ground level, explosions.
Click to expand...

I know what you are positing, but where (other sources, science, other sites) are other examples of compression (or longitudinal) waves leaving the kind of evidence I'm pointing out from the relief map of Alabama, i.e. lower elevation? Thanks.
Click to expand...

As far as I know this one is the grand daddy of them all. I've seen what compression waves can do up close and personal thanx to some unpleasant military experiences. But this one is so big that studying it is going to be clear blue sailin'. To say unprecedented would be an understatement. But yes there has been a lot of research done on the ground effects of powerful explosions. That's how we learned how to build bunker-busting bombs. But that's science the the military likes to keep to themselves. A weapon is more effective if no one knows how to prepare for it's effects. And digging for that stuff is when you start seeing the DOD warning pages about attempting to access confidential systems.
Sorry but you can call me chicken. I got scared and quit prodding them.
 
You really might want to get a copy of Firestone, West and Warwick-Smith's book. There are a LOT of images in there that will blow your mind.
 
That outer ring is a red hearing. If you want to get a handle on the power of the thing take some core samples of the blast center. Say, within 5 miles of Marshal alabama.
 
Here's an exerpt from some recently published research:

Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas coolingR. B. Firestonea,b, A. Westc, J. P. Kennettd, L. Beckere, T. E. Bunchf, Z. S. Revayg, P. H. Schultzh, T. Belgyag, D. J. Kennetti, J. M. Erlandsoni, O. J. Dickensonj, A. C. Goodyeark, R. S. Harrish, G. A. Howardl, J. B. Kloostermanm, P. Lechlern, P. A. Mayewskio, J. Montgomeryj, R. Poredap, T. Darrahp, S. S. Que Heeq, A. R. Smitha, A. Stichr, W. Toppings, J. H. Wittkef, and W. S. Wolbachr
aLawrence Berkeley National Laboratory, Berkeley, CA 94720; cGeoScience Consulting, Dewey, AZ 86327; dDepartment of Earth Sciences and eInstitute of Crustal Studies, University of California, Santa Barbara, CA 93106; fNorthern Arizona University, Flagstaff, AZ 86011; gInstitute for Isotope and Surface Chemistry, H-1525, Budapest, Hungary; hDepartment of Geological Sciences, Brown University, Providence, RI 02912; iDepartment of Anthropology and Museum of Natural and Cultural History, University of Oregon, Eugene, OR 97403; jEastern New Mexico University, Portales, NM 88130; kSouth Carolina Institute of Archaeology and Anthropology, University of South Carolina, Columbia, SC 29208; lRestoration Systems, LLC, Raleigh, NC 27604; mRozenstraat 85, 1018 NN, Amsterdam, The Netherlands; nBureau of Mines and Geology, University of Nevada, Reno, NV 89557; oClimate Change Institute, University of Maine, Orono, ME 04469; pUniversity of Rochester, Rochester, NY 14627; qDepartment of Environmental Health Sciences, University of California, Los Angeles, CA 90095; sP.O. Box 141, Irons, MI 49644; and rDepartment of Chemistry, DePaul University, Chicago, IL 60614


Nature of the Event. The evidence points to an ET event with continent-wide effects, especially biomass burning, but the size,density, and composition of the impactor are poorly understood. Even so, current data suggest that this impactor was very different from well studied iron, stony, or chondritic impactors (e.g., at the K/T boundary). The evidence is more consistent with an impactor that was carbon-rich, nickel–iron-poor, and therefore, most likely a comet. Although the current geologic and geochemical evidence is insufficient to fully understand impact dynamics, we can offer speculation for future work.
Toon et al. (46) suggest that an impact capable of continent-wide damage requires energy of 107 megatons, equivalent to an impact by a _4-km-wide comet (figure 1 in ref. 46). Although an impactor that size typically leaves an obvious large crater, no such late Pleistocene crater has been identified. The lack of a crater may be due to prior fragmentation of a large impactor, thereby producing multiple airbursts or craters. Hypervelocity oblique impact experiments (P.H.S., unpublished data) indicate that a low-impedance surface layer, such as an ice sheet, can markedly reduce modification of the underlying substrate if the layer is equal to the projectile’s diameter. These results suggest that if multiple 2-km objects struck the 2-km-thick Laurentide Ice Sheet at _30°, they may have left negligible traces after deglaciation. thus, lasting evidence may have been limited to enigmatic depressions or disturbances in the Canadian Shield (e.g., under the Great Lakes or Hudson Bay), while producing marginal or no shock effects and dispersing fine debris composed of the impactor, ice-sheet detritus, and the underlying crust.
Toon et al. (46) also noted that if airbursts explode with energy of 107 megatons at optimum height, they will cause blast damage over an area the size of North America that is equivalent to a ground impact of 109 megatons (figure 5 in ref. 46). Such airbursts effectively couple the impactor’s kinetic energy with the atmosphere or surface (47, 48), producing devastating blast waves well above hurricane force (70 m_s_1) (46). In 1908, at Tunguska, Siberia, a object _150 m in diameter, either a carbonaceous asteroid or a small, burned-out comet, produced a _15-megaton airburst with an intense fireball (107 °C) that scorched_200 km2 of trees and leveled _2,000 km2 of forest yet produced no crater or shock metamorphism (49). A debris shower from a heavily fragmented comet (11) would have produced an airburst barrage that was similar to, although exponentially larger than Tunguska, while causing continent-wide biomass burning and ice-sheet disruption, but again possibly, without typical cratering.

Environmental Effects. The YD event would have created a devastating, high-temperature shock wave with extreme overpressure, followed by underpressure, resulting in intense winds traveling across North America at hundreds of kilometers per hour, accompanied by powerful, impact-generated vortices (50–52). In addition, whether single or multiple objects collided with Earth, a hot fireball would have immersed the region near the impacts and would have been accentuated if the impact angles were oblique (46, 53). For comparison, Svetsov (48) calculated that a Tunguska-sized airburst would immerse the ground with a radiation flux severe enough to ignite 200 km2 of forest within seconds. Thus, multiple, larger airbursts would have ignited many thousands of square kilometers.At greater distances, the reentry of high-speed, superheated ejecta would have induced extreme wildfires (53), which would have decimated forests and grasslands, destroying the food supplies of herbivores and producing charcoal, soot, toxic fumes, and ash. The number of ET airbursts or impacts necessary to induce the continent-wide environmental collapse at 12.9 ka is unknown.

Yep! Sounds about right.
 
BAD TYPO!
Where post above says 107 megatons, and 109megatons read 107 megaton, and 109 megaton I couldn't correct it after posting.
Sorry :-[
Then I figured out how to fix it. :-[

I Have the entire paper in a PDF file if anyone is interested. It's pretty exiting stuff.
 
There is a map included in PDF that shows all the locations of the Clovis sites they took samples from. Much hard, sweaty field work.

There are no Clovis sites in the blast zone I've pointed out. :shock:

This gets more interesting every day.
 
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