An American Icon - Canyon Diablo

Did the impact vaporize thousand of tons of nickel iron?

For as long as I can remember, the crater was known to me.

An early memory, but I don't know exactly how I first saw it, or where.

Figure 1. The classic photograph.

But when my family was heading to Stanford, CA, we stopped at the crater. And I walked the rim you see in the photo above.

Now, I'm lucky to have one of its fragments, big as my hand and heavy.

Figure 2. A fragment over 500 grams.

As a child, my parents had some of the great paleontology coffee-table books, and I was captured by the thought of open grassland – the Pleistocene with spots of woods.

I thought about the mammoths and mastodons, saber-toothed cats, glyptodons, ground sloths, Irish elk, cave bears and camels, the first horses – and a fireball trailing smoke followed by a mushroom cloud, vaporizing the surrounding lands.

Through these years, I've come to learn that almost everyone has seen a photograph of the great American crater – even when in Wales, Great Britain, the kids knew of the crater.

It's an American Icon – like the Grand Canyon, or Yellowstone.

Here's what it looks like from space:

Figure 3. NASA. Taken December 14, 1982 by the Landsat satellite.

The gully southwest of the crater is Canyon Diablo, which drains northward into the Little Colorado River and then into the Colorado River in the Grand Canyon. U.S. Interstate 40 can be seen running east-west across the top of the picture.

But what's the history of the crater? And why so many existing fragments of this great American iron?

History

The story of Meteor Crater, also named Barringer, began 50,000 years ago.

An asteroid traveling over 40,000 miles per hour plunged toward Earth. Estimated to be 80 feet in diameter, the nickel-iron meteor weighed around 60,000 tons. As it tried to tear through the sky, it broke apart from pressures caused by Earth's atmosphere -- a main mass and tens of thousands of fragments.

When it hit, in only seconds, the main meteorite blasted open Meteor Crater, lifting millions of tons of sandstone and limestone, spraying molten rock and pieces of stone – some as large as houses – and destroying life for miles around.

Here's a map of the distribution of some of the smaller meteorite shards:

Figure 4.

It is estimated that more than 80 percent of the meteorite that formed the crater vaporized into a hot mushroom cloud of meteoritic metal, calculated at 1.7 megatons of energy (the equivalent of 1.7 million tons of TNT). A monstrous blast.

Note The Hiroshima explosion was estimated at 15 kilotons (the equivalent of 15,000 tons of TNT).

But when the dust and debris settled and the melted rock cooled, the crater sat quietly for tens of thousands of years, and the Arizona climate changed from grassland into dry scrub.

Humans On the Plateau

Early man moved into the area – the Dawn Men, the first aboriginal inhabitants, followed by the Basket Makers, then the Pueblo (Periods I and II).

Figure 5. Mojave Indian dwellings at Canyon Diablo, Arizona.

American Environmental Photographs Collection, [AEP Image Number, e.g., AEP-MIN73], Department of Special Collections, University of Chicago Library.

It was the later people who built dwellings in the cliffs of the Canyon Diablo, just miles from the crater, and which the meteorite was eventually to be named after.

Archaeological finds throughout the United States and Mexico, proved that Canyon Diablo fragments were venerated by several Native American tribes and had been traded briskly centuries before Columbus reached the shores of the New World.

Unfortunately, the crater eventually became an example of how modern man frequently misjudged meteorite craters... as well as how they have learned.

The Study of the Crater

For example, In 1891, G. K. Gilbert, a US Senior Geologist, proclaimed that the crater in Arizona was the result of a volcanic steam explosion rather than an impact of a meteorite. An this view continued to last for a long time.

However, in 1903, Daniel Barringer, lawyer-mining engineer-geologist, recognized the crater as a potential site for mining iron and nickel, and so he staked mining claims on the site.

To give you a sense of the time, here's the Trading Post Barringer might have visited.

Figure 6. Canyon Diablo Navajo Trading Post in 1903.

Unfortunately, Barringer continued for 20 years to locate a large iron mass but died in 1929 without success.

In 1908, George P. Merrill, another US geologist, suggested the meteorite may have vaporized on impact. Around 1928 astronomer F. R. Moulton was hired by the Board of Barringer's company to see if the company should continue looking for a large mass of iron.

Moulton adjusted the estimates as to the size of the meteorite, and he argued that the explosion caused by the impact resulted in total vaporization of the meteorite. It was the information that stopped the mining at Meteor Crater.

In the 1930's H. H. Nininger started working for the Museum in Denver Colorado and looking for meteorites throughout the U.S., but he spent time in and around Meteor Crater.

During a magnetic rake survey around the crater in 1939, he realized the discarded material passing through an eight-mesh screen might be the most important part of his study. So he bagged up a large sample of the discard for laboratory analysis and carried it back to Denver, but he did not get around to examining it.

Figure 7. Nininger's American Meteorite Museum, located across from Meteor Crater.

In 1946, Nininger moved out to the crater, and he began to make an extended search around it. There he found millions, or billions, of tiny little droplets of nickel iron distributed around the crater on the plains.

Here's a photo of two of his sample tubes of metallic spheroids.

Figure 8.

Nininger suspected during that summer in 1949 that he was finding the condensation products which Merrill had declared were lacking and which the Moulton explosion-theory seemed to require for its verification.

And this research was validated.

In 1999 scientists concluded that more than four-fifths of the meteorite was completely melted and spread over the Four Corners Region where Colorado, Arizona, New Mexico and Utah meet.

Figure 9. Molten droplets from an impact.

Most of the iron asteroid spread as an enormous expansion plume produced by gases released from Colorado Plateau limestone. A fraction of the melted material survived to form sand-grain-sized particles called "spheroids,” part of Nininger's term.

The 1999 study also concluded that the meteorite was traveling faster than what many had considered (45,000 mph) and was perhaps larger, 100 feet wide.

But as we learn more about meteorites, we look closer at how they were made and what they produced as they came to Earth.

Just The Specs

Canyon Diablo, Arizona

Fell between 20,000 and 50,000 years ago

Coarse Octahedrite

Found by European settlers around 1891

Composition:

Kamacite--this iron nickel alloy makes about 90 percent of specimens.

Taenite--the other iron nickel constituents taentie and plessite make up 1 to 4 percent of the material.

Schreibersite crystals occur as skeletal blades. This is a very hard mineral that will ruin a saw blade unfortunate enough to be put to the task of cutting a Canyon Diablo.

Troilite--this iron sulfide occurs as nodules up to 50 mm across or as elongated lenses. May be mixed with graphite, daubreelite, chromite, or base metal sulfides.

Graphite occurs as large bodies within iron or in separate masses.

Cohenite, an iron carbide, is common. This mineral is even harder than Schreibersite.

Haxonite, chromite and silicates are also found.

The specimens subjected to greater shock show partial melting, recrystallization, neumann banding and other deformation characteristics.

The most well-known shock effect is the transformation of graphite into diamond and lonsdaleite. These take the form of tiny dark masses that become evident on sawing. A diamond blade will move aside when it hits one of these.

Terms

As with other meteorites, the unique composition of Canyon Diablo can teach us about minerals, structure, our solar system, and ultimately the world we live on.

Definition of Cohenite

n. An iron nickel carbide mineral [(Fe,Ni)3C] that occurs as an accessory constituent of iron meteorites, including all coarse octahedrites containing 7 percent nickel or less.

http://www.mineralienatlas.de/lexikon/index.php/MediaDataShow?mineralid=792&backlink=Cohenit

Definition of Graphite

n. Graphite is a mineral made of carbon. Diamond and elemental carbon are also forms of carbon.

Graphite has a sheet-like crystal structure with light bonding between the sheets, which is what makes it good for pencil leads. It is easy to rub off the sheets of graphite.

A graphite nodule from a Canyon Diablo meteorite.

http://www.meteorite-times.com/Back_Links/2006/April/Jims_Fragments.htm

Definition of Man's Struggles

n. Barringer built a small home at the rim of the crater in 1910, which burned down in the mid 1940s.

Remnants of the house still exist.

http://punkyboy.com/americais/2003_12_01_archive.html

Definition of Meteorite Diamonds or Carbonados

n. Another mineral form of carbon. Generally black and opaque, believed to have formed from shock pressure and heating during the impact of an asteroid with the Earth.

Small and often hard to find since they are usually mixed up with other minerals near or in graphite nodules; they are also found in Canyon Diablo meteorites. They ruined the grinding wheels that were not nearly as hard as the diamonds.

A rare form of hexagonal "diamond" known as Lonsdaleite is also found in Canyon Diablo meteorites.

http://www.meteorite-times.com/Back_Links/2006/April/Jims_Fragments.htm

Definition of Schreibersite

n. An iron-nickel-phosphorous mineral, brittle, silvery in color and seen in iron meteorites as needles that align with the crystal structure of the metallic portions of the meteorite. Can be in lacy borders around troilite nodules and can tarnish to a bronze color.

Schreibersite enclosing a small graphite nodule.

http://www.meteorite-times.com/Back_Links/2006/April/Jims_Fragments.htm

Definitions of Taenite and Kamacite:

n. Two nickel-iron minerals that make up the metal portion of octahedrite family meteorites. Wider strips of kamasite will generally be separated by thinner strips of taenite.

The light kamacite bands are bordered by darker taenite ribbons.

Hexahedrites are essentially iron meteorites of solid kamacite, while ataxites are essentially iron meteorites of pure taenite.

(These other two types of iron meteorites will not display a Widmanstätten Pattern when etched though they will often show other types of lines and features which distinguish them from man-made irons and steels.)

http://www.meteorlab.com/METEORLAB2001dev/widpatrn.htm

Definition of Troilite

n. An iron-sulfide mineral commonly found with graphite in iron meteorites. Characterized by its bronze color and by the fact that it will dissolve in weak acid and leave a brown stain on the slice.

A nodule of troilite on the left and graphite on the right.

http://www.meteorite-times.com/Back_Links/2006/April/Jims_Fragments.htm

Links

Here's a link to a video of the Mesa Verde National Park (Est. 1906) archaeological site. This will give an understanding of the type of structures and history that the dwelling ruins at Canyon Diablo were a part of.

Location: Colorado, United States
Culture: Anasazi, Ancestral Puebloans
Era: Prehistoric, Basketmakers, Modified Basket-Makers, Developmental Pueblo, Classic Pueblo
Site Description: The renowned cliff dwellings, the height of the Puebloans' architecture, include more than 600 units. With such a wealth of sites to manage, the National Parks Service called on CyArk to emulate current documentation techniques with new digital technologies to demonstrate the advantages and capabilities of high definition survey and documentation.

http://www.youtube.com/watch?v=0UfNE4FfEwA&feature=player_embedded#

Here's an indepth video about Ancestral Puebloans:

http://www.youtube.com/watch?v=52aoSCLkwS4&NR=1

Here's an interview with H. H. Nininger, done in 1976:

“but in 1923, in the fall, I saw this big fireball come across one evening … while I thought I'd been pretty well educated, I had never heard anything about meteorites ... Then came this fireball a couple of weeks later, and I was all cocked and primed and started right in to chase that fireball. Been at it ever since!”

http://www.nau.edu/library/speccoll/images/text/txt/38181.htm#a01

Arizona Meteor Crater Photo Gallery, Photographs by Fred Espenak:

http://www.mreclipse.com/Observatory/Crater/Crater.html

Anatomy of an Impact (Great illustrations - Steps)

http://www.mnh.si.edu/earth/text/5_3_2_0.html

Formation of Meteor Crater - Video

http://www.sciencedata.net/downloads/demo/collisionsimpacts/meteorcraterformation.htm

Here's 100 tons of explosives being destroyed. This can give you an idea of what a small meteorite may look like when hitting the Earth. Note the hot metal falling, but imagine tens of thousands of tons:

http://www.youtube.com/watch?v=5K_bDFmyB_k&feature=related

Figures & Acknowledgments

Figures

Figure 1. Photo from Wikimedia Commons.

Figure 2. Photo from Aerolite Meteorites.

Figure 3. Image from NASA. Photo from the NASA Visible Earth website

Figure 4. From http://www.meteoritemarket.com/CDinfo.htm

Figure 5. http://memory.loc.gov/cgi-bin/query/h?ammem/aep:@field%28NUMBER+@band%28icuaep+azs12%29%29

Figure 6. http://www.legendsofamerica.com/AZ-CanyonDiablo.html

Figure 7. http://www.meteorite.com/nininger/nininger-moments-6.htm

Figure 8. From http://www.marmet-meteorites.com/id28.html

Figure 9. From http://www.mnh.si.edu/earth/text/5_3_2_0.html