Thursday, August 25, 2011

Lubang Akibat Meteor

Impact craters are formed when a meteoroid, asteroid or comet crashes into a planet or a moon. All the inner bodies in our solar system have been heavily bombarded by meteoroids throughout their history. This bombardment is clearly visible on the surfaces of the Moon, Mars and Mercury for example. On the Earth, however impact craters are continually erased by erosion or transformed by tectonics over time.

Still, almost 170 terrestrial impact craters have been identified on our planet. These range in diameter from a few tens of meters up to about 300 km (186 miles), and they range in age from recent times to more than two billion years. The impact craters featured on this list are relatively small and young making them easier to spot. An example of a large and old impact crater is the Chicxulub crater with a diameter of 180 kilometers (110 miles). The impact that formed this famous crater is thought to have been responsible for the extinction of the dinosaurs, about 65 million years ago.

 Kaali Crater
Around 660 BCE, a meteor entered the earth’s atmosphere, broke up into at least 9 pieces, and impacted the Baltic island of Saaremaa with the force of a Hiroshima-type atomic bomb. Some of the craters later filled with groundwater but retain their characteristic circular shape as they were formed long after Ice Age glaciers retreated. The largest Kaali crater is about 300 ft (100 meters) in diameter and is filled with groundwater, the level of which varies with the seasons.

The Kaali event may have impacted more than just the land; hints of what must have been a terrible human tragedy can be found in ancient Viking and Finnic epic poems as well as in Norse mythology. The main Kaali crater has been called “Holy Lake” and it may have been used in pagan rituals.

Gosses Bluff Crater, Australia
Gosses Bluff crater looks pretty good for its age: about 142 million years! Located in Australia’s Northern Territory, the ruggedly beautiful crater features a central ring of peaks that soar 500 ft (150 m) into the crystal clear Outback skies. A popular tourist destination (but perhaps not for the cruise & cabana set), Gosses Bluff crater can be found about 110 miles west of the town of Alice Springs

The arrival of the Gosses Bluff bolide was the ultimate “Jurassic park”, causing widespread devastation and leaving an impact crater 13.5 miles (22 km) in diameter. Time has left its mark, local climate conditions notwithstanding, and currently the Gosses Bluff crater is “only” 3 miles (5 km) wide.

Lonar Crater Lake, India
One of India’s most famous meteorite impact craters is the Lonar crater lake, located near the town of Sultanpur in India’s Maharashtra state. Measuring just over a mile wide from rim to rim, the crater is partially filled by a salty, alkaline lake 3,900 feet (1,200 meters) in diameter. The Lonar crater was created by the impact of a comet or meteor in the Pleistocene epoch roughly 52,000 years ago

Lonar crater retains much of its original shape and appearance, due in part to the lack of glaciation in that area of India and also the hardness of the volcanic basalts which make up much of the region’s bedrock.

Monturaqui Crater
The Monturaqui Crater is located south of the Salar de Atacama in Chile. The present dimensions of the crater are approximately 460 meter (1,509 feet) in diameter by 34 meter (100 feet) deep. The impact probably occurred about a million years ago. Because of the extreme arid conditions of the area the crater is still clearly visible. By its size and morphology, the Monturaqui crater presents many similarities with the Bonneville crater on Mars explored by the Spirit rover in 2004. Both craters are shallow, the size of the blocks ejected near the crater rim are similar, and both were formed in a volcanic environment.

Roter Kamm Crater
Located in the Namib Desert, Namibia, the Roter Kamm crater is about 2.5 km (1.6 miles) in diameter and is 130 meters (400 feet) deep. It was created by a meteor with a size of a large vehicle about 3.7 million years ago. The crater is clearly visible, but its floor is covered by sand deposits at least 100 meters (300 feet) thick. Combined with the orangey-red color of the Namib Desert the crater gives the impression of a Martian surface rather than that of our own planet.

Tswaing Crater
The Tswaing Crater was created by a chondrite or stony meteorite, some 30 to 50 meter in diameter, that hit the earth about 220,000 years ago. In the center of the crater is a small lake which is filled by a spring and rainwater. Stone tools from the stone age show that the crater was regularly visited by people in order to hunt and collect salt. European settlers named the region Zoutpan (Salt Pan) while the local Tswana tribes call the region Tswaing which means “Place of Salt”.

Pingualuit Crater, Quebec, Canada
Discovered in the mid-1940’s but known to indigenous native people as the “Crystal Eye of Nunavik”, Pingualuit crater is the site of a meteor impact that occurred approximately 1.4 million years ago. The lake that today fills the crater is fed only by rain and snow, resulting in exceptional water purity with a salt content of just 3 ppm (the Great Lakes average 500 ppm).

Formerly known as the New Quebec Crater, Pingualuit crater is located in Quebec’s far northern Ungava peninsula and measures 2.14 miles (3.44 km) in diameter.

Amguid Crater
A relatively young crater, the Amguid Crater is the result of a meteor impact about 100,000 years ago. It is located in a remote area in southwestern Algeria. The perfectly circular meteorite impact crater is 450 meter (1476 feet) in diameter and 30 meter (100 feet) deep. The top of the rim is covered by blocks of sandstones that are several meters in diameter. The center of the crater is flat, and is filled by compacted eolian silts.

Wolfe Creek Crater, Australia
Like Meteor Crater in Arizona, Wolfe Creek crater owes its well-preserved state to both age (around 300,000 years) and the environment of the Australian Outback. Approaching the crater on land, visitors must first climb over the 80 ft (25 meter) high rim before descending to the sand-covered crater floor 165 ft (50 meters) below the rim.

Both oxidized iron meteorite fragments and pieces of impact glass (formed when sand is melted) have been found in the area of the half-mile wide Wolf Creek crater, attesting to its astronomical origins. As well, the center of the crater is dotted with outcroppings of gypsum, a white mineral that holds water and allows for the growth of trees and shrubs in the otherwise inhospitable desert.

Barringer Crater Arizona, USA
Located about 40 miles east of Flagstaff, the 4,000 ft wide and almost 600 ft deep Meteor Crater owes its startlingly lunar aspect to both a relatively young age (about 40,000 years) and the arid climate of the northern Arizona desert in which it is situated. It’s estimated that the mainly nickel-iron Canyon Diablo Meteorite was about about 55 yards (50 meters) in diameter and weighed approximately 150,000 tons.

Meteor Crater is, perhaps surprisingly, privately owned and has remained the property of the Barringer family since 1903. Tourists are charged a $15 entrance fee by Meteor Crater Enterprises and a visitor’s center on the crater rim offers multimedia presentations and a chance to handle meteoric iron fragments found in the area.

Baca Juga

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