Transcript MeteorCraterText

Impact features
Meteor Crater
near Flagstaff, AZ
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Instructor has
no financial
or other
interest in
Meteor
Crater.
It’s just a neat
place to see.
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Characteristics
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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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• Barringer’s 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.ca:80/crater/
– index_e.html
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• Gilbert’s arguments in favor of volcanic
origin
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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
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Couldn’t 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
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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
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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
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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 (don’t 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
Copernicus
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3/6/02
Isidorus, Moon
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Theophilus, Moon
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3/6/02
Gosses Bluff, Australia
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