Arizona
Meteor Crater
The Arizona Meteor Crater is a
meteorite impact crater located about 35 miles east of Flagstaff, in
the Northern Arizona desert. The Crater site lies at an elevation of
about 5709 feet above sea level. It is about 4,000 feet in diameter,
some 570 feet deep, and is surrounded by a rim that rises 150 feet
above the surrounding plains. The center of the crater is filled with
700-800 feet of rubble lying above crater bedrock.
Formally known as the Canyon Diablo
Crater, it was created about 50,000 years ago when the local climate on
the Colorado Plateau was much cooler and damper. At the time, the area
was an open grassland dotted with woodlands. It was uninhabited by
humans, the first of whom are thought to have reached North America
only around 13,000 years ago.
The object which excavated the
crater was a nickel-iron meteorite about 54 yards across, which
impacted the plain at a speed of several miles per hour. The speed of
the impact has been a subject of some debate. Modeling initially
suggested that the meteorite struck at a speed of up to 45,000 mph, but
more recent research suggests the impact was substantially slower,
28,600 mph. It is believed that about half of the impactor's 330,000
tons bulk was vaporized during its descent, before it hit the ground.
The explosion dug out 175 million
tons of rock. The shock of the impact propagated as a hemispherical
shock wave that blasted the rock down and outward from the point of
impact, forming the crater. An impact energy, equivalent to an
estimated 6.5 megatons, was released into the atmosphere and generated
a devastating above-ground shock wave. Limestone blocks as massive as
30 tons were tossed outside the crater's rim, and debris from the
impact has been found over an area of 100 square miles.
All life within a radius of three
to four kilometers would have been killed immediately. The impact
produced a fireball hot enough to cause severe flash burns at a range
of up to 7 miles. A shock wave moving out at 1,200 mph leveled
everything within a radius of up to 13.5 miles, dissipating to
hurricane-force winds that persisted to a radius of 25 miles.
At the following links are photographs of the extraordinary geologic
site.
Ref:
Wikipedia Encyclopedia – updated 19 November 2007