Sunday, January 10, 2016

Dreams of Summer: The Bad Star Strikes! What happened at Canyon Diablo 50,000 Years Ago

It might be heresy for me to say it, but there are some places where the geology appears to be kind of...monotonous. Flatlands covered by soils are sometimes not all that interesting. I can even be accused of thinking this way about my very own home valley, the Great Valley of California. I've spent a long time teaching my students that our valley isn't actually boring at all. It's just that the best parts are beneath the surface.

Just the same, parts of the Colorado Plateau can be a bit monotonous too. The region between Flagstaff and Holbrook is a case in point. There just isn't much to see as you travel east on Interstate 40 except for the San Francisco Peaks Volcanic Field receding in the distance. The sage and grass-covered plains don't offer much in the way of interesting sights. But there is one really big exception. At Canyon Diablo there are some hills visible south of the highway that seem a bit out of place. They aren't high, but there is nothing like them elsewhere in the area.
Disasters happen. Sometimes, the nature of the disaster is predictable, as when one sees a river rising prior to flooding. A volcano that is shaking and producing ash suggests that an evacuation might be smart. We had just left such a place a few hours earlier, at Wupatki and Sunset Crater National Monuments. Sometimes disasters happen, and there's simply no way to be warned.

50,000 years ago, this barren plain was slightly less barren. The region was a savanna/woodland populated by horses, bison, antelope, sloths, and mammoths. They were hunted by American Lions, Sabertooth Cats, Dire Wolves and Cave Bears. The sky lit up, maybe for a moment brighter than the sun. The incoming meteor would not have appeared to move across the sky, because it was headed directly at this spot, at a speed estimated between 28,000-45,000 mph. Maybe the light would have grown in brightness and in size, but there were only a few seconds to respond. And what to do? There was nowhere to run. The chunk of rock was about 160 feet across when it impacted with the surface. The explosion was comparable to a large atomic explosion. The resulting crater was about 3,900 feet (1,200 meters) in diameter, and some 570 feet deep (170 meters). The chunk of iron and nickle was obliterated into small bits (in the early years efforts were made to drill for the large chunk thought to be buried within the crater). The largest piece found so far is the Holsinger Meteorite, which weighs 639 kilograms (1,409 lb).
The Holsinger Meteorite at the Meteor Crater Museum

The word "disaster" has an interesting etymology. It literally translates as "bad star". Meteors may be called falling stars, but they are made of the leftovers from the formation of the Solar System. On the other hand, the raw materials of meteorites, the iron, nickle and other elements, were forged in the core of gigantic stars, so in a sense it is fair to think of a meteorite as a "bad star".

A large impact can be a horrific disaster. A few years back in 2013, astronomers were monitoring an asteroid chunk that was going to make a close pass by Earth, but that same day a different chunk several yards across hit the atmosphere from another direction. It exploded with the strength of a large atomic bomb, shattering thousands of windows in the Russian town of Chelyabinsk. It was about 65 feet (20 meters across). If such a chunk hit the surface near a city, the effects would be incalculable. A large strike in the oceans has the potential to produce destructive tsunamis. A meteorite several miles wide probably caused the extinction of the dinosaurs and around 60% of all species of life known from 65 million years ago.

In the big picture, Meteor Crater was a localized event. It destroyed life over an area of 100 square miles (260 square kilometers) or more. And yet the scale of the hole is hard to appreciate. Look at the white patch in the bottom of the crater in either of the pictures above. The spots are fenced off, and the owners have placed a life-sized astronaut for scale. Can you see the astronaut below?

The crater is privately held, but the owners have done a nice job of preserving the crater and have constructed an extensive museum and viewing area. They are very accommodating for geology field trips if you contact them in advance. For more information about visiting the crater, check out

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