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can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body. In most common usage, the term is used for the approximately circular depression in the surface of a planet, moon or other solid body in the Solar System, formed by the hyper-velocityimpact of a smaller body with the surface.
and they range from small, simple, bowl-shaped depressions to large, complex, multi-ringed impact basins. Meteor Crateris perhaps the best-known example of a small impact crater on the Earth.
Daniel Moreau Barringer (1860 – 1929) • a geologist best known as the first person to prove the existence of a meteoritecrater on the Earth, the Meteor Crater in Arizona.
The site was formerly known as the Canyon Diablo Crater, and the meteorite that created the crater is officially called the Canyon Diablo Meteorite, the name that is on all officially labeled fragments of the meteorite. Scientists refer to the crater as Barringer Crater
Eugene Merle Shoemaker • He studied the impact dynamics of Barringer Meteor Crater, located near Winslow, Arizona. To understand the dynamics, Shoemaker inspected craters that remained after underground atomic bomb tests at the Nevada Test Site at Yucca Flats. He found a ring of ejected material that included shocked quartz (coesite), a form of quartz that has a microscopically unique structure caused by intense pressure.
Crater formation • involves high velocity collisions between solid objects, typically much greater than the velocity of sound in those objects. Such hyper-velocity impacts produce physical effects such as melting and vaporization. • Impacts at these high speeds produce shock waves in solid materials, and both impactor and the material impacted are rapidly compressed to high density. Following initial compression, the high-density, over-compressed region rapidly depressurizes, exploding violently, to set in train the sequence of events that produces the impact crater
Three distinct stages of processes of crater formation: • initial contact and compression • Excavation • modification and collapse
Contact and compression impactor first touches the target surface (This contact accelerates the target and decelerates the impactor) both the impactor and the target close to the impact site are irreversibly damaged and it continues moving away from the impact behind the decaying shock wave.
Excavation Contact, compression, decompression, and the passage of the shock wave all occur within a few tenths of a second for a large impact. The subsequent excavation of the crater occurs more slowly, and during this stage the flow of material is largely sub-sonic. During excavation, the crater grows as the accelerated target material moves away from the impact point. The target's motion is initially downwards and outwards, but it becomes outwards and upwards. The flow initially produces an approximately hemispherical cavity. The cavity continues to grow, eventually producing a paraboloid (bowl-shaped) crater in which the centre has been pushed down, a significant volume of material has been ejected, and a topographically elevated crater rim has been pushed up. When this cavity has reached its maximum size, it is called the transient cavity.
Modification and collapse • In most circumstances, the transient cavity is not stable: it collapses under gravity. In small craters, less than about 4 km diameter on Earth, there is some limited collapse of the crater rim coupled with debris sliding down the crater walls and drainage of impact melts into the deeper cavity. The resultant structure is called a simple crater, and it remains bowl-shaped and superficially similar to the transient crater. In simple craters, the original excavation cavity is overlain by a lens of collapse breccia, ejecta and melt rock, and a portion of the central crater floor may sometimes be flat.
Simple crater • A meteorite impact crater of relatively small diameter, characterized by a uniformly concave-upward shape and a maximum depth in the center, and lacking a central uplift.
Complex crater • the collapse and modification of the transient cavity is much more extensive, and the resulting structure is called a complex crater. The collapse of the transient cavity is driven by gravity, and involves both the uplift of the central region and the inward collapse of the rim.
View from the north rim of Meteor Crater(Barringercrater,Arizona)first-recognized terrestrial impact crater
Closeup of old mine shaft at the bottom of the crater. Note astronaut cutout and flag attached to fence (inset)
The Canyon Diablo meteorite comprises many fragments of the asteroid that impacted at Barringer Crater (Meteor Crater), Arizona.
The Chesapeake Bay impact craterwas formed by a bolide that impacted the eastern shore of North America about 35 million years ago, in the late Eocene epoch. It is one of the best-preserved "wet-target" or marine impact craters, and the largest impact crater in the U.S. Continued slumping of sediments over the rubble of the crater have helped shape Chesapeake Bay.
The collision between Earth and an asteroid a few kilometers in diameter may release as much energy as several million nuclear weapons detonating simultaneously.
The Chicxulub crater (English is an ancient impact crater buried underneath the Yucatán Peninsula in Mexico. Its center is located near the town of Chicxulub, after which the crater is named. The crater is more than 180 km (110 mi) in diameter, making the feature one of the largest confirmed impact structures on Earth; the impacting bolide that formed the crater was at least 10 km (6 mi) in diameter.
Chicxulub, Yucatan Peninsula, Mexico Half of the species on Earth became extinct including the dinosaurs
Wolfe Creek, Australia19°10' S, 127° 48' E; rim diameter: 0.875 kilometers (.544 miles); age: 300,000 years Wolfe Creek is a relatively well-preserved crater that is partly buried under wind blown sand. The crater is situated in the flat desert plains of north-central Australia. Its crater rim rises ~25 meters (82 feet) above the surrounding plains and the crater floor is ~50 meters (164 feet) below the rim. Oxidized remnants of iron meteoritic material as well as some impact glass have been found a Wolf Creek. This photograph is a south-looking, oblique aerial view of the crater.
Some extraterrestrial impact craters Mariner 10 photomosaic of Caloris Basin on Mercury,
colour view of the Hellas Planitia region on Mars created from images taken by the Viking orbiters.
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