Meteor Crater

IT MUST HAVE BEEN A HELL OF AN EXPLOSION!

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In this diary, we head to Arizona and find ourselves in an entirely different planed topography, where a sizable visitor from outer space made a great big hole in the landscape, Meteor Crater. Like the San Rafael Swell desiring a national monument status, this privately owned facility wouldn't mind having the same status. However, so far the crater is dubbed a landmark. Question is: Would you pay to see this crater pictured above? Some 200,000 annual visitors think it's worth the time. You tell me. Meanwhile, this diary's virtual tour can be thought of as partially extraterrestrial and terrestrial. But you will find no aliens and spacecraft here. Best you drive farther east after the tour and visit Roswell, New Mexico for that sort of thing.


Location/Geography
In east central Arizona, about 43 mile east of Flagstaff (exit 233, I-40). Closest city: Winslow. High desert country at an elevation of about 5,709 feet above sea level.

Spotlight
Gaping cosmic crater, the first such discovered by humans. Focus: recent human history, speculation, meteorites and geology.

Snapshot
Some 50,00 years ago, a rather large meteorite slammed into this region. Its impact left a gaping saucer-shaped crater and this so-called impacter surely made a big noise and created a brilliant explosion heard and seen for hundreds of miles. Of course, there were no humans around to witness such a startling event. Today, the preserved impression remains a significant and altered topographical contour because of the desert climate of this region. Desert environs also tend to preserve rather than erode or fill. Through the years this relatively sizable indent has been called by various names: the Canyon Diablo Crater (Devil Canyon), Canyon Diablo Meteorite, and the Barringer Crater. In time, today’s designate Meteor Crater found favor because of a regional and former Arizona Post Office named Meteor. The meteor, an anomaly from outer space, left its astral hallmark about 3.5 miles west of Devil Canyon. Daniel Barringer was the first to suggest the aberrant extraterrestrial footprint had been produced by a meteorite. The crater is also privately owned by the Barringer family under the auspices of the Barringer Crater Company. This company proclaimed the crater was the first proven, best preserved meteorite crater on earth. So far, this assertion remains unchallenged. More about this point is explained further along. To date, there have been roughly one hundred-seventy impact craters discovered around the world. Meteor Crater measures 4,000 feet in diameter and 570 feet in depth. The crater is surrounded by a rim that rises 150 feet above the surrounding desert plains. The center of its basin is filled with 700 to 800 feet in depth of spent rubble lying above the crater bedrock.

Diagram of an impact crater structure:


From an article originally appeared in the Space Science Reference Guide, Second Edition, Lunar and Planetary Institute, 2003.


Guided Tour Essentials
One of the more notable features of Meteor Crater’s extraterrestrial visitor is its squared-off outline. Believed to be caused by preexisting regional jointing (cracks) in the strata at the impact site, the telltale crater was created during the Pleistocene Epoch (2.5 million to 12,000 years ago). This geologic epoch is also a fairly recent period of repeated glacial advances on a global scale; a time when the local climate on the Colorado Plateau was much cooler and more humid. Hence, the entire region was not the desert landscape we see today. It was instead a vast, open grassland accented with woodland and marshy places. Hard to believe the region once looked like this, but it's true. More than likely no humans lived here, though such primitive beasts as wooly mammoths and giant ground sloths freely roamed. The flash of the large object penetrating the atmosphere must have been frightening to these and other life forms that witnessed the spectacle. That nickel-iron meteorite was once estimated by scientists to be 54 yards across. Its blazing mass slammed into the plain at a speed of several kilometers per second. However, in recent years the meteor's momentum has been a subject of debate.


Regardless its speed, its signature sure left a sizable impression!

Initially, modeling suggested the meteorite struck at a speed of up to 45,000 miles per hour (equates to 20 kilometers per second), while more recent researchers suggest the impact was substantially slower, possibly closer to 28,600 m.p.h. (12.8 k.p.s.) is more accurate. There are also questions about the actual size of the meteor at time of impact. For example, this later estimate of impact speed relies on the general assumption the meteor was roughly half the original size of 330,693 short tons (300,000 metric tons) in bulk. Before it even struck the ground, the crater had partially vaporized, then after the impact fragments were blown from the surviving mass. Thus very little of the original mass remains. The only physical evidence we have is its gaping impression. Fortunately, due to the predominant dry climate it's as if this monstrous-sized ball of rock from outer space had struck the ground just weeks or months ago. Visitors traveling I-40 take the exit and take time-out to see this epic crater site, simply to see the awesome and destructive power of what meteors can do once their mass penetrates the atmosphere and makes landfall. True, it's wide-open desert terrain, mostly flat and habitual scenery, but for a change it's the destination that counts, not the journey.


Look out below!

Geology
This particular meteorite has the composition and classification of iron octahedrite (the most common class of iron meteorites and primarily composed of the nickel-iron alloystaenite (one of four known Fe-Ni meteorite minerals), which has a high nickel content, andkamacite (a major constituent of iron meteorites), which is the opposite. Other minerals include graphite (carbon), chromite (iron magnesium chromium oxide), base metal sulfides,troilite (a variety of the iron sulfide mineral, pyrrhotite), and haxonite (iron nickel alloy). Haxonite is also the most common component. However, people generally figure meteorites are nickel-iron anomalies and let it go at that.


What impactors look like up close (only most 'shooting stars' through the atmosphere are about the size of pea or at best the size of a nickel.

The Discoverers
Grove Karl Gilbert, chief geologist for the United States Geologic Service (USGS), was the first official investigator of the crater in 1891. However, he erroneously concluded that it was the result of a volcanic steam explosion (caused by groundwater mixing with hot lava or magma). Although he knew what an impact crater was, Gilbert assumed that if the mutant impression was caused by a meteorite, then the volume of its crater, as well as meteoritic material, should be present on the rim. Gilbert then made another erroneous assumption: He assumed that a large portion of the meteorite should still be buried in those relatively greater depths and therefore would generate a large magnetic rarity. Indeed, his base calculations showed the volume of the crater and the debris on the rim were roughly equivalent so that the mass of the hypothetical impactor was missing. Moreover, he discovered there were no magnetic anomalies. From this assertion, he deduced that meteorite fragments found on the rim were simply coincidental. In 1892, Gilbert would also be among the first to propose that the moon's craters were caused by impact rather than volcanism. One out of two findings––not bad!

Grove Karl Gilbert portrait



Daniel Barringer was the next to explain the enigmatic crater. A mining engineer and astute businessman, in 1903 he countered Grove's hypothesis by suggesting the crater had been produced by the impact of a large iron-metallic meteorite. Barringer's company, the Standard Iron Company, soon filed for a patent on the property which was approved by by President Theodore Roosevelt. Barringer marked off 640 acres (2.6 sq. km) around the center of the crater, defining the boundaries of the site. His claim was further divided into four quadrants which he named, coming from the center clockwise from northwest, Venus, Mars, Jupiter and Saturn. Clever, that. Three years later, President Roosevelt authorized the establishment of a newly named Meteor, Arizona, Post Office. (Until then the closest Post Office was in Winslow, some 30 miles). The disputed crater (by scientists) was officially on the map. Between 1903 and 1905, Standard Iron Company conducted research on the crater's origins and confirmed Barringer's findings: The crater had indeed been caused by an impactor from outer space. Barringer and his partner, Benjamin Chew Tilghman, a mathematician and physicist, also a soldier and inventor, documented evidence for the impact theory in papers presented to the USGS. Initially, Barringer's arguments were met with skepticism because of a reluctance to consider the role of meteorites in terrestrial geology. Nevertheless, he persisted and sought to bolster his theory by locating the remains of the meteorite itself (with the assumption Gilbert might be correct about such remains deeper below the ground). At the time of first discovery by Europeans, the surrounding desert plains were found to be littered with about 30 tons (27 metric tons) of large oxidized iron meteorite fragments. From this evidence Barringer believed the bulk of the impactor could still be found beneath the crater floor.

Daniel Berringer



FYI
The oldest known impact crater was fairly recently discovered to have slammed into the Earth in what is now Greenland (reported 6/28/2012). It is claimed a massive asteroid or comet collided with our planet a billion years before any other known collision. (http://www.sciencedaily.com/...) Previously, it was thought the oldest known crater had formed roughly 2 billion years ago. Scientists tells us those awesome and telltale lunar craters were also formed in the same way sometime between 3 and 4 billion years ago. It is also thought the Earth in its early forming must have experienced even more collisions at this time (because it was the larger of the two bodies).
From history’s perspective, Barringer’s reasoning was sound. The science of impact physics, however, was also poorly understood in those years. He was also unaware that most of the meteorite had vaporized upon hitting the ground. Indeed, he spent twenty-seven years trying to locate a large deposit of meteoric iron. During his lengthy search, he drilled to a depth of 1,376 feet, yet no significant deposit was ever found. Part of his passion for the project came from ambitious plans for mining the iron ore. He estimated from the size of the crater that the meteorite had a mass of some 100 million tons (90,720,000 metric tons). Ironically, the current estimate of 300,000 tons (272,155 metric tons) is closer to the truth. Iron ore of the type found at the crater was also highly valued at the time, selling for one hundred and twenty-five dollars a ton. In effect, Barringer believed he was searching for a mother lode worth more than a billion dollars! Although many geologists remained skeptical of the crater's meteoritic origins, as recently as the 1950s the notion became more acceptable. That’s because planetary science had gained notable acceptance in understanding cratering processes. Thus it is the value of knowledge shifted away from economics and headed, instead, toward science.

Enter the next important thinker in Meteor Crater's evolution of thought and origin, Eugene M. Shoemaker, a renown professor of geology then and now. He was also one of the founders of the specialized field of planetary science. It wasn't until 1960 that he confirmed Barringer's hypothesis. The key discovery was the presence in the crater of the mineral stishovite(extremely hard, dense tetragonal form––polymorph––of silicon dioxide). This mineral is a rare form of silica found only where quartz-bearing rocks have been severely shocked by excessive heat and an instantaneous overpressure. However, he realized extreme overpressure cannot be created by volcanic action. Instead, the only known mechanisms of creating such results is either naturally through an impact event or artificially through a nuclear explosion. Professor Shoemaker's discovery is considered the first definitive proof of an extraterrestrial impact on the planet's surface. Since then, numerous impact craters have been identified around the world (which he found numerous settings). For example, Tuscany, Italy's crater-shaped terrain, and Siberia's Popigai and Tunguska craters. Nonetheless, Meteor Crater remains one of the most visually impressive impressions in the planetary crust due to its size, young age and lack of vegetation.



Astral Geology-Turned-Terrestrial
The impact created at Meteor Crater is called an inverted topography. This geologic term refers to landscape features that have reversed their elevation relative to other local features. Such abrupt changes to landscape most often occur when lower areas become filled with lava or sediment. Later, the lava (or sediment) congeals into a material that is more erosional resistant than the base material surrounding it. In short, it’s a process of differential erosion that removes the less resistant surrounding material, leaving a residue of the younger and have resistant material. This remaining material may then appear as a telltale ridge where previously there was a valley. In the case of Meteor Crater, the layers immediately exterior to its rim are stacked in an opposite order than they normally occur. Thus the impact overturned and inverted the layers to a distance of between 1 to 1.2 miles outward from the crater's edge. Climbing the rim of the crater from the outside, the formations from top-to-bottom, also oldest-to-youngest in this order are the following: Coconino Sandstone, Toroweap Formation, Kaibab and Moenkopi (270 million to 200 million years ago). However, in the interior of the crater the layers are in the expected order.


Visitor Center
The crater site remains the property of a private consortium held by the original owners and may someday be designated a national monument. Situated on the north rim of the crater, the totally new and improved Meteor Crater's Visitor Center has recently changed its former mediocre display to a series of kiosks that thoroughly explain the history and science of what happened here long ago. The center also features interactive science exhibits and displays about meteorites and asteroids, space, the solar system and comets. A large-screen theater and movie production shows and explains the background to help visitors visually comprehend the nature of this or any impact crater.

The Visitor Center also features the American Astronaut Wall of Fame, including an Apollo boilerplate command module (a nonfunctional craft, system, or payload which is used to test various configurations and basic size, load, and handling characteristics.




Previously mentioned, a 1,406 pound (637 kilogram) meteorite found in the area is also on display, as well as meteorite specimens from Meteor Crater that can be touched.


Bonus Details
The nearly two hundred impact craters discovered on the planet's surface range in diameter from a few tens of feet/meters up to a whopping 186 miles. These craters range in age from very recent (the Sikhote-Alin craters in Russia, whose creation were witnessed in 1947) to more than 2 billion years ago. However, most are fewer than 201 million years old because of geological processes that obliterate older craters. Generally, impact craters are found in stable interior regions of continents. To date, very few undersea craters have been discovered. The reason has to do with difficulty of surveying the sea floor; also, the ocean bottom changes fairly rapidly. Oceanic physiographic changes include the subduction process of tectonic plates into the deeper interior of the planet, which easily disguises what could be hundreds of larger meteorite strikes from millions to billions of years ago. Certainly, impact craters are not to be confused with other landforms that might appear similar. For instance, calderas (collapsed volcanoes) and ring dikes (intrusive igneous bodies) resemble crater impressions.

Sometimes Size Really Does Matter
As remarkable as is Arizona's Meteor Crater, it is still not among the forty-two largest impact craters thus far discovered. The five largest are Vredefort (South Africa) at 186 miles in diameter, Sudbury (Ontario, Canada) at 155 miles, Chicxulub (Yucatan, Mexico) at 105 miles, Manicouage (Quebec, Canada) at 60 miles and Popigai (Siberia) at 60 miles. For the United States, Chesapeake Bay is sixth on the list at 55.9 miles. Despite Meteor Crater ranking for size, it's still considered the best preserved and certainly one of the most attractive impact craters this side of the moon.

Directions
From Flagstaff, Arizona, take I-40 east, 43 miles and about halfway between Winona and Winslow (Exit 233). Site is 6 miles south of the interstate.


Contact Information
Meteor Crater Enterprises, Inc., P. O. Box 30940, Flagstaff AZ 86003-0940. Phone (administrative office) 800-289.5898; local 928-289.5898; Fax 289.2598. Email: non-listed.

One of the most celebrated sci-fi films has its conclusion here at Meteor Crater:


I'll leave you with some of the most memorable dialogue in this film. It's between the Starman (played by Jeff Bridges) and the SETI guy who is trying to help him escape (played by Charles Martin Smith):
Mark Shermin: Have people from your world been here before?
Starman: Before yes. We are interested in your species.
Mark Shermin: You mean you're some kind of anthropologist? Is that what you're doing here? Just checking us out?
Starman: You are a strange species. Not like any other. And you'd be surprised how many there are. Intelligent but savage. Shall I tell you what I find beautiful about you?
[Shermin nods]
Starman: You are at your very best when things are worst.
Parting shots:



That sort of thing went on a long time ago (and there will be other impactors visiting from beyond). Just be thankful for our atmosphere. Otherwise, we might have looked like this:


Parting artist's poster shot (one of my favorites, and so is this classic airplane):


And so we come to the end of another trail, another armchair tour. There will be other scenic places to tour and more supplemental topics to read and think about, so stay tuned for a continuation in this series.

As always, your thoughtful commentaries are welcomed.

Happy Trails!

Rich

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