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TITLE: Anatomy of an Impact


The impact of a large meteorite blasts out a crater, leaving an array of changes in the local rocks. Studies of man-made explosions and high-velocity impact experiments using special laboratory “guns” have helped scientists understand the sequence of events that forms an impact crater.

[Photo: Meteorite Impact]





See caption at right.

In and Around the Crater
The compressed rocks rebound immediately, causing an explosion that blasts out huge quantities of material. Much of this debris falls back to Earth around and in the crater.

The shock wave pulverizes surrounding rock, and the incredible pressure creates distinctive new minerals.

In a hypervelocity collision, the heat is so intense that it completely melts rocks at and near the point of impact. That molten rock turns solid again and becomes glass.

 

See caption at right.

Beneath the Crater
The shock wave also generates distinctive fracture patterns known as shattercones beneath the crater. The cones point toward the impact site and are mainly visible in deeply eroded Earth craters.

When the melt turns solid again, it forms a black rock called pseudotachylite.

The intense shock wave radiating from the point of impact crushes the rock below the crater and generates friction between the broken fragments. This friction melts part of the rock.

 

See caption at right.

Far From the Crater
Some large impacts squirt molten droplets of target rock into the atmosphere—and sometimes even above it. These droplets can land thousands of kilometers from the impact site, sprinkling vast areas of the Earth, known as strewn fields, with chunks of glass called tektites. Microtektites—much smaller bits of glass—shower even larger areas.


Giant layered tektites fall near impact site.

[Photo: Giant Layered Tektite]
   

Splash-form tektites have droplet or splash-droplet shapes.

[Photo: Splash-form tektite]
   

Flanged tektites shoot above atmosphere and remelt at reentry, taking on aerodynamic shapes.

[Photo: Flanged Tektite]

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Smithsonian National Museum of Natural History Department of Mineral Sciences website Credits