Impact features

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Impact features

• Meteor Crater
• near Flagstaff, AZ

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Instructor has no financial or other interest in
Meteor Crater. Its just a neat place to see.
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Characteristics

• Bowl-shaped
• raised rim (100 feet)
• diameter 4000 feet
• depth 600 feet
• fragments of an iron meteorite in vicinity
  (Canyon Diablo meteorite)
• 25,000 - 50,000 years old
• volcanoes nearby (5 million years old)

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Meteor Crater, Arizona
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History

• 1876 Mathias Armijo, cowboy
• visited by prospectors, metal fragments
• thought to be volcanic
• 1891 sample of metal sent for analysis
• 77 iron
• 2 lead
• rest gold and silver

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• 1891 A E Foote, a mineralogist, visits
• identifies metal fragments as a meteorite
• diamonds found in meteorite
• crater due to impact
• 1895 G K Gilbert, Director USGS
• not an impact
• volcanic
• 1902 D M Barringer, mining engineer
• graduated Princeton at 19
• law school

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• studied geology at Harvard
• wanted to work in west
• discovered Commonwealth silver mine, AZ
• rich
• visited crater site, was of meteorite origin
• bought the place!
• 1906 published paper outlining his ideas
• B convinced that a large (several million tons)
  iron meteorite buried below the crater, worth
  250,000,000

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• Barringers arguments in favor of impact origin
• surrounded by millions of tons of debris
  pulverized sandstone (Coconino)
• oxidized chunks of iron
• meteorite fragments mixed with rock debris
• overturned rim
• no volcanic rocks in crater
• no magnetic effect - iron in small pieces

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Detailed history and info.

• www.barringercrater.com/adventure
• www.meteorcrater.com/
• gdcinfo.agg.nrcan.gc.ca80/crater/
• index_e.html

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• Gilberts arguments in favor of volcanic origin
• no evidence of a large meteorite
• no magnetic effect from meteorite
• not necessary to have lava in the crater
• crater the result of high pressure steam

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Test A. volcanic - no magnetic effect volumes
equal B. impact - should be a magnetic effect,
unequal volumes Gilbert measured and A was
correct
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Barringer

• Drilling in center - nothing
• decided that the meteorite buried beneath south
  rim
• 1919 Gilbert reiterates volcanic theory
• 1920 B raises more money drill sticks and breaks
  - meteorite?
• 1925 mine shaft - floods, company sinks, B dies

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Geology

• Couldnt be simpler (layer cake)
• horizontal layers of sedimentary rocks
• each of a different color
• only three rocks involved
• lowest is the Coconino sandstone (white)
• middle is the Kaibab limestone (buff)
• uppermost is the Moenkopi sandstone (purple)

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Layer-cake arrangement of sedimentary
rocks youngest on top excavation rim deformation
of the rocks
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New player

• Eugene Shoemaker
• PhD from Princeton University
• doctoral dissertation, 1960 - Meteor Crater
• idea that a high velocity object hitting the
  Earth would be largely vaporized
• old idea - 1908
• now the ability to simulate with computer

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Mid 1960s
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Estimates

• Iron meteorite
• 100 feet in diameter
• 63,000 tons
• 15 km/sec
• energy 120 megatons of TNT
• greater than the nuclear device dropped on
  Hiroshima

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High velocity example

• Buffalo - New York is 450 miles
• 730 km
• at 15 km/sec, the trip would take 49 seconds
• meteorites can have velocities of 70 km/sec
• trip to NY would take 10 seconds
• And you would be driving a car that weighed
  63,000 tons (dont hit anything!)

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In spite of that - Meteor Crater is a small event.
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Underground nuclear test Project Sedan
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Overturned rim reversal of rocks
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Overturned rim oldest rock on top
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Crater types bowl shaped, small raised
rim Meteor Crater central peak larger terraces C
opernicus
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Isidorus, Moon
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Theophilus, Moon
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Gosses Bluff, Australia