With thousands or perhaps millions of asteroids and
comments navigating through our solar system, relatively few have
impacted our planet in recent geologic time. Though those that did
left their mark. Here we displays a sampling of such impack
craters.
As an example: A 50 meter object released the energy of a 5 megaton
nuclear warhead!
In a Sandia Laboratories computing scenario, an asteroid
1.4 kilometers in diameter was simulated to strike the Atlantic Ocean 25
miles south of Brooklyn, N.Y. To model the event the scientists broke up
a 120-square-mile space that roughly approximates the New York City
metropolitan area, the air above, and the water and earth below.
Sandia's teraflops supercomputer then calculated what happened inside
each cube as the asteroid splashed down. This produced a
three-dimensional model of the collision.
The simulation takes into account the real-world laws of physics
governing time, temperature, pressure, gravity, the densities of water
and earth, and thousands of other considerations to create an accurate
prediction. Here's what it showed:
This computer-generated image by Sandia National
Laboratories' scientists shows the impact of a 1-km comet (or asteroid)
hitting in the open ocean. The comet and 300 to 500 cubic kilometers of
ocean water would be vaporized nearly instantaneously by the tremendous
energy of the impact. The impact energy of about 300 gigatons of TNT
would be equivalent to about 10 times the explosive power of all the
nuclear weapons in existence in the 1960s at the height of the Cold War.
Five seconds after a 1.4 kilometer-wide asteroid
crashes into the Atlantic Ocean off the coast of New York, an impact
plume containing superheated water, earth, and other debris blankets
major portions of Long Island. The viewpoint is from orbital altitude
from a location about 100 kilometers west of New York City looking east.
Long Island trails off in the distance. Manhattan and Staten Islands are
in the foreground.
Eleven seconds after impact, Long Island and the
New York shoreline are engulfed in debris and superheated steam, and
much of the material in the upper portions of the impact plume is on
suborbital trajectories. In both images, water is blue, land is brown,
water vapor is white, and hot material (greater than 5,000 Celsius) is
orange.
In other words, within minutes all of Metro New York
is vaporized. The plume would carry debris as far as California.
Most of central North America is destroyed.
Victoria Crater on Mars: A powerful camera aboard the
Mars Reconnaissance Orbiter, flying nearly 186 miles over the
planet's Victoria Crater, is taking spectacular close-ups of the
Martian surface for the first time.
A large impact crater on Venus
about 30 km (19 mi) in diameter is surrounded by a fresh ejecta
blanket. The extreme brightness of the blanket is due to its
roughness and its ability to scatter the radar signals that are
used to collect these images. Scientists believe that the
missing section of the ejecta blanket is due to an atmospheric
blast that followed the impactor as it crashed through the
Venusian atmosphere.
Artist's depiction of the Chixulub KT Impact Crater in
what is now Mexico - 1,000 years after impact (William K. Hartman)
Shuttle Radar Topography Mission (SRTM)
image of the Chicxulub Impact.
Image courtesy of Gary L. Kinsland - from Kinsland et al. 2003.
Image courtesy of Gary L. Kinsland.
The
Chicxulub
Crater was created 64.98 million years ago by an asteroid
approx. 6 miles in diameter. The crater in the Yucatan
Peninsula of Mexico has a diameter of 170 kms.
Aorounga, Chad, Africa - has a
diameter of 17 kilometers, with an age of 200 million years.
The impact of an asteroid or comet several hundred million years ago
left scars in the landscape that are still visible in this
spaceborne radar image of an area in the Sahara Desert of northern
Chad. The original crater was buried by sediments, which were then
partially eroded to reveal the current ring-like appearance. The
dark streaks are deposits of windblown sand that migrate along
valleys cut by thousands of years of wind erosion. The dark band in
the upper right of the image is a portion of a proposed second
crater. Scientists are using radar images to investigate the
possibility that Aorounga is one of a string of impact craters
formed by multiple impacts. Note in the photo above, there is
indication of two other craters in the upper right and left. Source:
Solarviews.com
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. Source:
Solarviews.com
Mistastin Crater, a heavily eroded
complex structure. Eastward moving glaciers have drastically reduced
the surface expression of this structure, removing most of the
impact melt sheet and breccias and exposing the crater floor.
Glacial erosion has also imparted an eastward elongation to the
crater that is particularly evident in the shape of the lake that
occupies the central 10 kilometers (6 miles) of the structure.
Horseshoe Island, in the center of the lake, is part of the central
uplift and contains shocked Precambrian crystalline target rocks.
Just beyond the margins of the lake are vestiges of the impact melt
sheet that contains evidence of meteoritic features in quartz,
feldspar and diaplectic glasses. Source: Solarviews.com
These twin circular lakes (large dark
features) were formed simultaneously by the impact of an asteroidal
pair which slammed into the planet approximately 290 million years
ago. The lakes are located near the eastern shore of Hudson Bay
within the Canadian Shield in a region of generally low relief in
northern Quebec province. Notice that the larger western structure
contains a ring of islands with a diameter of about 10 kilometers
that surrounds the center of the impact zone. They constitute a
central uplifted area and are covered with impact melts. The central
peak of the smaller Clearwater Lake East is submerged. The lakes are
named after their exceedingly clear water. Also notice that the
surrounding terrain shows widespread scarring from glaciation. The
multitude of linear and irregular shaped lakes (dark features) are
the result of gouging or scouring action caused by the continental
ice sheets that once moved across this area. Source:
Solarviews.com
Popigai Crater - Russia
100km diameter crater created 35
million years ago.
Aeromagnetic image of the
Acraman area of the Gawler Craton, covering the Landsat
scene (see image below). ER Mapper file: total magnetic
intensity, pseudocolor (Gaussian equalisation histogram
stretch), sun angle from the northeast. From Williams,
Schmidt and Boyd (1996).
Source:
University of New Brunswick
Landsat scene covering most
of the Acraman impact structure in the Mesoproterozoic
Gawler Range Volcanics, showing: 1, Lake Acraman within the
Acraman depression; 2, Lake Gairdner; 3, Lake Everard; 4,
the Yardea corridor at 85-90 km diameter. Surface water
(darker blue) in Lake Gairdner helps define an arcuate trend
(5) at ~150 km diameter that continues westward to Lake
Everard. X marks the
location of a central dipolar magnetic anomaly in the
southeastern part of Lake Acraman. Landsat scene 15 February
1973, scene center S31-30 E135-51. From Williams, Schmidt
and Boyd (1996).
The
Acraman
crater located in South Australia state, Australia has a
diameter of 90 km and was created approx. 590 million years
ago..
Manicouagan Crater in
northern Canada is one of the oldest impact craters known.
Formed about 200 million years ago, the present day terrain
supports a 70-kilometre diameter hydroelectric reservoir in
the telltale form of an annular lake. The crater itself has
been worn away by the passing of glaciers and other
erosional processes. Still, the hard rock at the impact site
has preserved much of the complex impact structure and so
allows scientists a leading case to help understand large
impact features on Earth and other Solar System bodies. Also
visible above is the vertical fin of the Space Shuttle
Columbia from which the picture was taken in 1983.
Barringer (Winslow) crater in Arizona
is actually one of the smaller examples with a diameter of 1.2km and
depth of 570ft. The impact occurred 49,000 years ago
Around 142.5 million years ago the
Gosses Bluff Crater was formed by an object thought to be around 600
meters in diameter. The crater you see today is smaller than the
original due to erosion. Its diameter currently stands at 5km, the
original diameter is thought to have been closer to 20km.
Vredefort Crater, Johannesburg, South Africa
- with a diameter of approx. 300km,
Vredefort basin in South Africa is currently the largest confirmed
impact crater on Earth, and also one of the oldest at 2 billion
years. The crater was the result of an extreme impact with an object
whose diameter was 10km.
Bosomtwe Crater, Lake Bosomtwe,
Ghana - the actual impact crater which
hosts Lake Bosomtwe is 10.5km in diameter, the lake itself is
presently 7km. The impact took place 1 million years ago. The
crater has been eroded due to overflow from the lake.
This picture shows the spectacular
Kara-Kul structure. Partly filled by the 25-kilometer (16-mile)
diameter Kara-Kul Lake, it is located at 3,900 meters (12,900 feet)
above sea level in the Pamir Mountain Range near the Afghan border.
Only recently have impact shock features been found in local
breccias and cataclastic rocks. Source: Solarviews.com
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