Meteor Crater

by Garrett Gough and Trisha Whipple 
MeteorCrater1
An aerial photo of Meteor Crater, the visitor center can be seen on the lower left of the rim, for scale.

Meteor Crater (see figure 1) is not just a large whole in the ground. It serves as both the most well preserved impact site and most widely studied impact crater to date (Shoemaker 1963).  One reason it is so well preserved is that it formed relatively recently in geological terms, only about 50 Ka. 

The Holsinger Meteorite is the largest fragment recovered from the larger 150 ft meteor that was responsible for the formation of Meteor Crater.
The Holsinger Meteorite is the largest fragment recovered from the larger 150 ft meteor that was responsible for the formation of Meteor Crater.

Meteor Crater sits near the southern edge of the Colorado Plateau in north-central Arizona, approximately thirty miles east of Flagstaff. This bowl-shaped depression is three quarters of a mile across and six hundred feet deep. It is thought to have been caused by a meteorite that was 130 to 150 feet across and composed of nickel and iron (Roddy et al., 1980) (See Figure 2).  The formations exposed at the site range from mid-late Permian to Triassic in age.

Sutton (1985) studied shock-metamorphosed sandstone and dolomites originally from the Coconino and Kaibab formations, respectively, found at Meteor Crater.  Using thermoluminescence, Sutton was able to precisely date the age of the impact to 49,000 +/- 3000 years before present.  In addition to the Coconino and Kaibab formations, there is also the Moenkopi and the Toroweap also exposed at the site. The Moenkopi is Triassic, everything else is Permian. 

A cross section of all the formations present at Meteor Crater, at and below the surface.
A cross section of all the formations present at Meteor Crater, at and below the surface.

The two noteworthy minerals found in Meteor Crater were coesite and stishovite. Coesite requires enormous temperature and stishovite requires extreme pressure to be formed (see figure 3). “Shocked” rocks are indicative of meteorite impacts because the extremely high temperatures and pressures that generally follow immediately after an impact do not occur naturally on Earth (Shoemaker 1960, 1963).

 Shoemaker (1960, 1963) compared craters created by nuclear explosions to meteoritic impacts and found that they had many similarities. They shared the same general shape and also featured the inversion of the stratigraphic sequence of beds around the rim, features that are the result of an extremely large amount of energy. The meteorite is thought to have been moving very fast at the time of impact; over 12 km/sand generated an explosion equivalent to fifteen megatons of TNT (Shoemaker, 1960, 1963).

A panorama of Meteor Crater from the  north side balcony outside of the museum (taken by Trish Whipple in March, 2014)
A panorama of Meteor Crater from the north side balcony outside of the museum (taken by Trish Whipple in March, 2014)

It is clear from the size of the crater, how much energy was involved (see figure 4). The size and the recrystallization from the impact show the energy, but to get to see what we were reading and learning about up close, to be able to be at that location and visualize on site what it was like to be there 50,000 years ago, helped to fully understand everything that we learned about in a whole new way. We were no longer just reading about it, it was real.       

References Cited

Roddy, D.J., Schuster, S.H., Kreyenhagen, K.N., and Orphal, D.L., 1980, Computer code simulations of the formation of Meteor Crater, Arizona: Calcualtions MC-1 and MC-2: Proceedings of the Eleventh Lunar and Planetary Science Conference, New York, Pergamon Press, p. 2275-2308.

Shoemaker, E.M., 1960, Penetration mechainics of high velocity meteorites, illustrated by Meteor Crater, Arizona: International Geological Congress, 21st, Copenhagen, pt. 8, p. 418-434.

Shoemaker, E.M., 1963, Impact mechanics at Meteor Crater, Arizona, in Middlehurst, B. and Kuiper, G.P., eds., The moon, meteorites, and comets; The Solar System, Volume 4: Chicago, Illinois, University of Chicago Press, p. 301-336.

Sutton, S.R., 1985, Thermoluminescence measurements on shock-metamorphosed sandstone and dolomite from Meteor Crater, Arizona: 2. Thermoluminescence age of meteor crater: The Journal of Geophysical Research, v. 93, p. 3690-3700.