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Kaali is a group of 9 meteorite craters in the village of Kaali on the Estonian island of Saaremaa. Formed more than 4,000 years ago (the age of the sediments at the bottom of crater lake), and possibly as long as 7,600 years ago (estimates vary), it is a comparatively recent crater. It was created by an impact event and is possibly the only known major impact event that has occurred in a populated area. Prior to the 1930s there were several hypothesis about the origin of the crater, including theories involving vulcanism and karst processes. Its meteoritic origins were first conclusively demonstrated by Ivan Reinvald in 1928, 1933 and 1937. ==Formation== The impact is thought to have happened in the Holocene period, more than 4,000 years ago. Analysis of silicate spherules in Estonian bogs show that the possible age of the impact craters could be approximately 7,600 years.〔 Other studies show more recent ages, even 7th century BC.〔''Radiocarbon'', Vol. 8, (1966), p. 436.〕 The craters were formed by a meteor with an estimated impact velocity of between 10 and 20 km/s with a total mass of between 20 and 80 metric tonnes. The meteor arrived from the north-east.〔(【引用サイトリンク】title=Kaali Crater )〕 At an altitude of 5–10 km, the meteor broke into pieces and fell to the Earth in fragments, the greatest of which produced a crater with a diameter of 110 m and a depth of 22 m. The explosion removed approximately 81,000 cubic meters of dolomite and other rocks and formed a 7–8 km tall, extremely hot gas flow. Vegetation was incinerated up to 6 km from the impact site.〔 Kaali Lake ((エストニア語:Kaali järv)) is on the bottom of this crater. Eight smaller craters are also associated with this bombardment. Their diameters range from 12 to 40 meters and their respective depths vary from one to four meters. They are all within one kilometer of the main crater. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Kaali crater」の詳細全文を読む スポンサード リンク
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