Did You Know?
The impact craters on the moon from millions of years ago are still crystal clear, because of the absence of any atmosphere, as against the Earth which has an atmosphere, where pressure changes and weathering take place.
An impact crater is a circular depression formed on the surface of a planetary body due to the impact of another smaller body traveling at very high speeds. The Earth has 175 known impact craters, with a possibility of more which might have formed in earlier years. Impact craters are capable of causing substantial damage and environmental changes across a large area.
The formation of an impact crater consists of 3 stages:
- Contact and Compression Stage: As the solid body comes in contact with the surface, a shock-wave is generated. The solid body deforms and vaporizes.
- Excavation Stage: During the excavation process, the crater grows and starts spreading outward, away from the impact point. This creates a cavity, which continues to grow until it reaches its maximum size.
- Modification Stage: Once the cavity reaches its maximum size, the pressure over the inner side is relieved. If the crater formed is stable and is able to hold the position, it will remain as the same bowl-shaped crater. Although, if the crater is unstable, it tends to rebound after the pressure is released. This results in the formation of the 'central uplifts' and/or 'rings'.
Let's have a look at some interesting facts about few of the most well-known impact craters on our planet.
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Vredefort Crater
◎ Located in South Africa, it is the largest known impact crater on Earth.
◎ It is approximately 186 miles in diameter, and is believed to be about 2 billion years old.
◎ To make a crater of this size, the meteorite is believed to be about 6.2 miles across, traveling at around 22,000 mph.
◎ One cannot see the Vredefort Crater in totality from the ground or even from a considerable height. To have a complete view of the crater, you have to be at some point in space.
◎ The center of the crater consists of a dome of granite formed because of the liquified rocks splashing up when the high-speed meteor hit the surface.
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Barringer Crater
(Meteor Crater)
◎ It got its name from Daniel Barringer, who was the first to suggest that it was created due to a meteorite impact.
◎ This crater measures about 0.75 miles in diameter, and is 180 meters deep.
◎ It is approximately 50,000 years old.
◎ The meteorite that created the crater is believed to have weighed around 300,000 tons.
◎ The explosion was equivalent to 2.5 million tons of TNT.
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Chicxulub Crater
(Yucatán Peninsula Crater)
◎ The Chicxulub Crater was only recently unearthed, in 1978.
◎ It is roughly 105 miles in diameter, the third largest of all known craters on the Earth.
◎ It is about 65 million years old.
◎ It is believed to be the cause of extinction of the dinosaurs, because the impact created various global changes, including earthquakes, tsunamis, and global warming.
◎ Located underneath the Yucatán Peninsula in Mexico, it is largely underwater.
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Clearwater Craters
◎ This crater formed about 290 million years ago, and is located in present-day Quebec, Canada.
◎ It is a twin-impact crater, filled with water.
◎ The larger crater is 20.5 miles, whereas the smaller one is 13.7 miles in diameter.
◎ The Clearwater Lakes, as they are widely known, got this name due to the clear water they hold.
◎ While the central uplifted area (peak ring) is clearly visible in the larger, the smaller lake has it submerged.
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Manicouagan Crater
◎ This one is the largest crater that can be seen from the Earth itself.
◎ It is roughly 215 million years old. It has a concentric structure due the shock-waves of the impact.
◎ The inner diameter is about 40 miles, and the outer diameter is about 60 miles across.
◎ Its annular lake surrounds an island plateau called the René-Levasseur Island.
◎ It is the sixth-largest known impact crater on Earth.
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Karakul Crater
◎ Formed about 10 million years ago, it is located in Tajikistan near the border of Afghanistan.
◎ It remained unknown until it was located through studies of images taken from space.
◎ In totality, it is about 28 miles across in diameter, but is partially filled by a lake spanning about 16 miles.
◎ It is believed to be the highest crater, located approximately 4,000 meters above sea level.
◎ This crater was named after Queen Victoria, until it was renamed in the 1920s.
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Bosumtwi Crater
◎ This crater is approximately 1.3 million years old, about 6.5 miles wide, and is located in Ghana, Africa.
◎ It is almost entirely submerged in water. It is also known as Lake Bosumtwi.
◎ Before the asteroid impact, it was a rainforest full of animals.
◎ The lake is a popular location for local people who come around for activities like swimming, boating, and fishing.
◎ It consists of crystalline bedrocks.
On an average, the Earth experiences an impact once every million years. An impact event witnessed in our solar system was observed in 1994, when a comet broke apart and collided with Jupiter. This event provided a lot of knowledge about the reason the Earth and other inner planets have stayed protected because of Jupiter. Although it is difficult to predict an impact, the occurrence of such an event is improbable, at least for now.
