New Mexico Airburst Scars?

From Impact Melt Formation By Low-Altitude Airburst Processes, Evidence From Small Terrestrial Craters and Numerical Modeling. By H. E. Newsom, and M. B. E. Boslough we read:

“Airbursts in the lower atmosphere from hypervelocity impacts have been called upon to explain the nature of the Tunguska event and the existence of unusual impact-related silicate melts such as the Muong-Nong tektites and Libyan Desert Glass of western Egypt. Impact melts associated with impact craters, however, have been traditionally attributed to shock melting of the target material that experiences strong shock compression and heating. The characteristics of impact melts from small terrestrial craters (less than km diameter) leads to the possibility that the airburst phenomena may have been responsible for these melts. This conclusion is supported by numerical modeling of the airburst phenomena using super computer class facilities at Sandia National Laboratories.”

And, in a poster by Dr Boslough titled, The Nature of Airbursts and their Contribution to the Impact Threat. we read:

image

“Ongoing simulations of low-altitude airbursts from hypervelocity asteroid impacts have led to a
re-evaluation of the impact hazard that accounts for the enhanced damage potential relative to the standard point-source approximations. Computational models demonstrate that the altitude of maximum energy deposition is not a good estimate of the equivalent height of a point explosion, because the center of mass of an exploding projectile maintains a significant fraction of its initial momentum and is transported downward in the form of
a high-temperature jet of expanding gas. This “fireball” descends to a depth well beneath the burst altitude before its velocity becomes subsonic. The time scale of this descent is similar to the time scale of the explosion itself, so the jet simultaneously couples both its translational and its radial kinetic energy to the atmosphere. Because of this downward flow, larger blast waves and stronger thermal radiation pulses are experienced at the
surface than would be predicted for a nuclear explosion of the same yield at the same burst height. For impacts with a kinetic energy below some threshold value, the hot jet of vaporized projectile loses its momentum before it can make contact with the Earth’s surface. The 1908 Tunguska explosion is the largest observed example of this first type of airburst. For impacts above the threshold, the fireball descends all the way to the ground, where it expands radially, driving supersonic winds and radiating thermal energy at temperatures that can melt silicate surface materials. The Libyan Desert Glass event, 29 million years ago, may be an example of this second, larger, and more destructive type of airburst. The kinetic energy threshold that demarcates these two airburst types depends on asteroid velocity, density,
strength, and impact angle.

Airburst models, combined with a re-examination of the surface conditions at Tunguska in 1908, have revealed that several assumptions from the earlier analyses led to erroneous conclusions, resulting in an overestimate of the size of the Tunguska event. Because there is no evidence that the Tunguska fireball descended to the surface, the yield must have been about 5 megatons or lower. Better understanding of airbursts, combined with the diminishing number of undiscovered large asteroids,
leads to the conclusion that airbursts represent a large and growing fraction of the total impact threat.”

Ok, that’s pretty interesting stuff. But what if we don’t need to go all the way to Libya to find locations where a geo-ablative airburst has produced melt formations?

About 75 miles southeast of Albuquerque, New Mexico, there is a place that looks extremely promising. Beyond apparent patterns of material movements I see in the image data, I don’t know anything about the place. And field work remains to be done there. But, unless I miss my guess, at 34.482019, –105.573173 there is a four mile wide, multiple fragment, oblique impact, geo-ablative, airburst scar that may warrant a closer look.

16

I did a few impact experiments of my own, using various rifles, velocities, and target surfaces. Nothing formal, heck, I didn’t even take notes. But I can tell you that it is easy to make something like we see here happen in an experiment.

From 15 kilometers up, the material movements we see there seem to describe a four mile wide cluster of fragments hitting at low trajectory, from the west. And they must have shed a lot of velocity in the atmosphere.

If I’ve got it right, the target surface would’ve been a shallow lake. And the angle of impact was about 30 degrees.

We can use Google Earth’s ‘Historical Image’ function to look at different images of the same place. It’s a nice feature. Because it lets you see the same place at different times of the year, and in different lighting conditions. The black, and white, version of the place gives us a little better contrast to discern how the ejecta, was blown to the east from the main body of impacts.

16a

17 These oval splashes blown to the east have all the characteristics of splashes of impact ejecta from a cluster of small, oblique, fairly low velocity impacts into the sediments of a shallow lake.

 

18 All of these motion patterns are from west to east. Look closely, let’s zoom in on one impact point of a couple of the smaller fragments.

 

 

19The points of impact are on the western end of each oval splash. And I would love to go meteorite hunting in the pair of 45 meter depressions at 34.486357, –105.548684.

 

And when we look in the outlying areas we start to find places that look like they just might be a meteorite hunters dream.

21 Like the small, 70 meter crater at 34.40506, –105.677892

 

 

 

 

22 Or it’s neighbor just to the west at 34.407827, –105.683814

 

 

 

23 And I’m really curious to figure out how something like what we see at 34.407402, -105.693815 can happen.

 

 

24 Likewise at 34.406994, –105.693030

 

 

 

If you’re interested in helping, and you live close enough to go get a closer look at these features, and maybe grab a few rock samples, I’d sure like to hear from you.

Published in: Uncategorized on November 18, 2010 at 11:54 am  Comments (6)  

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6 CommentsLeave a comment

  1. Excellent find and post. Your finds are fascinating. Have you ever read a book called “Cataclysm” by Allan and Delair? It was sent to me by a prof at the Uni of Az. who thought I would find it interesting and I sure did. Even if I think a number of events are conflated by the authors, the evidence they marshall is amazing. I think you’d like it.

    • I hadn’t heard of it before. Thanks for the tip.

  2. Yeah, Dennis, this is a hell of a “blemish.” Probably insignificant, but just west of this along the same track about 7.5 miles there is a bit more scarring, nothing like the beauty of this one.

    As to the article, it solidifies much of what you’ve been saying. Whether you can tell from the comments or not, we do see your efforts as pointing to something quite valid and significant, no matter what the timing of it was – which may take a good bit of sleuthing to ever determine. So, we are on your side. Don’t doubt that. And this article supports much of what you’ve deduced.

    For impacts above the threshold, the fireball descends all the way to the ground, where it expands radially, driving supersonic winds and radiating thermal energy at temperatures that can melt silicate surface materials.

    This is a major conclusion in support of your understanding. The radiant heat “melts the surface materials” and then the “supersonic winds” – and pressure – have a chance to move the melted material around.

    Better understanding of airbursts, combined with the diminishing number of undiscovered large asteroids, leads to the conclusion that airbursts represent a large and growing fraction of the total impact threat

    Good. They are waking up to the danger.

    …the altitude of maximum energy deposition is not a good estimate of the equivalent height of a point explosion, because the center of mass of an exploding projectile maintains a significant fraction of its initial momentum and is transported downward in the form of a high-temperature jet of expanding gas. [emphasis added]

    I was just talking to Ed Grondine about comets and whether or not they actually might reach the ground. He argued that they do not impact, as I understood him. Perhaps he was leaning on the earlier understanding of the energetics, but this one seems to argue that at least the fireball does reach the ground ins ome cases of large “strong” ones. The “center of mass” as a “high-temperature jet” seems to be the same thing as an impact, though the characteristics, with the high temperature and expanding gas would be significantly different than a simple meteoric impact.

    Based on visual evidence such as you’ve been finding, it is quite apparent that there is a wide variety of ways this can manifest (and what evidence is left for us to discover). This paper seems to be moving toward acceptance of that viewpoint, which is great. Too narrow an idea of what CAN happen blinds researchers. It is very good to see that Newton and Boslough are widening the family of accepted types.

    You would probably agree with me that that widening is only just getting started.

    The kinetic energy threshold that demarcates these two airburst types depends on asteroid velocity, density, strength, and impact angle.

    I wonder specifically what is meant by asteroid “strength.” It’s cohesiveness? It’s degree of agglomeration?

    Since every incoming body has unique size, geometry, morphology and homogeneity, and every one will “graze” at a slightly different angle/elevation, it would seem that the features left by the air bursts will be different for every case, though maybe group-able into classes.

    This should be a great seminar for those able to attend.

    • By ‘strength’ I’m pretty sure he’s talking about it’s structural integrity of the object. Is it a solid, stony asteroid? Or a dense, solid iron? Or is it composed of a mixture of ices, and rock, in a loose conglomerate of fragments?

      From what I’ve been able to work out, it would appear there are a much larger variety of types than we have imagined.

  3. RE: Bumblebee cratoids (one at 34.406994 -105.693030)

    Could they be caused by a secondary smaller fragment hitting the raised rim of the first, sending ejecta out sideways only?

  4. I’am leaning towards the idea that some of the fragments may consist of highly explosive material. But with enough impurities to allow for an ablative shield that gets it through the atmosphere intact. So you get a two bowl crater. The larger bowl would be the result of the remaining kinetic energy. And the smaller, lobed structure that looks like the work of a shaped explosive charge is from a secondary detonation similar to a hydrogen peroxide explosion.

    A detailed description of the proposed explosive chemistry can be found in a paper by E. M. Drobyshevski titled  Tunguska-1908 and similar events in light of the New Explosive Cosmogony of minor bodies.


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