|[[ Sierra Madera Astrobleme. Photo by C.M. Mayo. ]]|
Driving east or west on I-10 or I-20 or 90 is to barrel along with the steady flow of big rigs, pickup trucks, RVs and SUVs; driving north-south, on the other hand, it gets very lonely, very strange, very fast.
Here is a photo* I took with my iPhone through the windshield while heading south on US-385 from Fort Stockton to Marathon. That jumble of hills over to the left is the Sierra Madera, which sits on the vast La Escalera Ranch, one of the largest ranches in Texas. Although I did not know it at the time, the highway was about to blaze me right through the Sierra Madera Astrobleme.
[*Normally I would never fool around with my smartphone while driving, but I had been driving out here for sometime and not seen a single vehicle, in either direction. I daresay I could have taken got out of the car and taken a siesta in the middle of the road.]
|[ Sierra Madera Astrobleme ]|
|[ Sierra Madera Astrobleme, |
off US-385 etween Fort Stockton and Marathon, Texas ]
The Sierra Madera is indeed on Google maps, but neither of the maps I carried with me that day, the AAA and the Geological Highway Map of Texas, noted it, so I was wholly unprepared for the sight, on the open plains, well before the Glass Mountains, of the strange-looking huddle of the Sierra Madera off to the east-- and all bathed in the golden-orange glow of sunset. Alas, my photo does not do its stunning gorgeousness a shred of justice.
It turns out that the Sierra Madera is an extremely rare "cryptoexplosion structure," in this case, a crater with a central mountain range raised not by volcanic or tectonic forces, but by the rebound from the impact of an unknown extraterrestrial object. The mountains and the approximately 6 mile-in-diameter crater, so eroded over some nearly 100 million years that I did not recognize it as I drove through it, are together known as the Sierra Madera Astrobleme.
An astrobleme is an eroded remnant of a large crater made by the impact of a meteorite or comet. The term, first used in the mid-20th century, is from the Greek astron, star, and blema, wound.
What was that object that slammed into the earth those nearly 100 million years ago? I have been searching the literature and have yet to come upon any description beyond "approximately spherical."
What was going on at the time? This would have been the Late Cretaceous or Early Tertiary, when Tyrannosaurus roamed and Quetzalcoatlus northropi, a pterosaur the size of a small jet airplane, cast his shadow from overhead.
The literature has a great deal of detail on shatter cones and various types of rock, as well as gravitational and magnetic anomalies. But as for a description for the layman, or shall we say, the average Tyrannosaurus Rex, of what the impact might have sounded like and how it might have affected the atmosphere, no dice. Undoubtedly, the blast was analogous to some flabbergastingly large quantity of TNT.
Dear reader, if you have more information about the Sierra Madera Astrobleme, please do write.
> University of Texas of the Permian Basin webpage on the Sierra Madera Astrobleme
All the crunchy geology. Plus the hypothetical reconstruction of the event.
> "Hydrocone Modeling of the Sierra Madera Impact Structure" by Tamara J. Goldin et al. Meteoritics and Planetary Science, 2006.
> "Geology of the Sierra Madera Cryptoexplosion Structure, Pecos County, Texas" by H.G. Wilshire, et al. U.S. Geological Survey Professional Paper No. 599, 1972.
Extra-extra-crunchy with shatter cones.
> United States Meteorite Impact Craters: Page on the Sierra Madera Crater
Good variety of photographs and information by Robert Beauford, PhD. He writes:
"This is one of the largest impact craters in the United States, and even after having worked on 4 to 5 km craters for several years, I found it challenging to take in the scale of the structure. It defines the shape of the vast, open landscape in every direction."> Purdue University's Impact Earth! Famous Craters page.
Alas, it does not include the Sierra Madera Astrobleme. But fascinating nonetheless.
> Astronaut's Guide to Terrestrial Impact Craters by R.A.F. Grieve, et al. LP Technical Report Number 88-03, Lunar and Planetary Institute, NASA, 1988
(See Sierra Madera, p. 13.)
P.S. Wiggy synchronicity du jour: Given that the Sierra Madera Astrobleme is near the Glass Mountains, it raised my eyebrows, rather somewhat, to come upon this webpage with the Ames Astrobleme Museum and the Gloss Mountains of Oklahoma:
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