Kaali crater

The crater as viewed from near the rim

The main crater is nearly circular. When the water level is low, rocks can be seen penetrating the surface: in the middle of the crater.

Tilted dolomite bedrock in the walls of the main crater

Kaali is a group of 9 meteorite craters located on the Estonian island of Saaremaa. Formed in the 7th century BC or about 4000 years ago (estimates vary), it is one of the most recent craters created by an impact event and the only known major impact event that has occurred in a populated area.

Prior to the 1930s, the main crater was thought to have been a volcanic caldera. Its meteoritic origins were first conclusively demonstrated by Ivan Reinvald in 1937.

Formation

The impact is thought to have occurred in the Holocene, around 4000 ± 1000 years ago. The craters were formed by an incoming meteor with an estimated impact velocity of between 10 and 20 km/s with a total mass of between 20 and 80 metric tonnes.

At an altitude of 5–10 km, the meteorite 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. Kaali Lake (Estonian: Kaali järv) exists in 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.

Effects

At the time of the impact, Estonia was in the Nordic Bronze Age and the site was forested with a small human population. The impact energy of about 80 TJ (20 kilotons of TNT) is comparable with that of the Hiroshima bomb blast. It incinerated forests within a 6 km radius.

In mythology

Scholars maintain that the event figured prominently in regional mythology. It was, and still is, considered a sacred lake. There is archaeological evidence that it may well have been a place of ritual sacrifice. At some point during the early Iron Age, the lake was surrounded by a stone wall measuring 470 meters in length, with a median width of about 2.5 meters and an average height of 2.0 meters.

Finnish mythology has stories that may originate with the formation of Kaali. One of them is in runes 47, 48 and 49 of the Kalevala epic: Louhi, the evil wizard, steals the Sun and fire from people, causing total darkness. Ukko, the god of the sky, orders a new Sun to be made from a spark. The virgin of the air starts to make a new Sun, but the spark drops from the sky and hits the ground. This spark goes to an "Aluen" or "Kalevan" lake and causes its water to rise. Finnish heroes see the ball of fire falling somewhere "behind the Neva river" (the direction of Estonia from Karelia). The heroes head that direction to seek fire, and they finally gather flames from a forest fire.

According to a theory first proposed by Lennart Meri, it is possible that Saaremaa was the legendary Thule island, first mentioned by ancient Greek geographer Pytheas, whereas the name "Thule" could have been connected to the Finnic word tule ("(of) fire") and the folklore of Estonia, which depicts the birth of the crater lake in Kaali. Kaali was considered the place where "The sun went to rest."

The main crater seen from front

Namesake

The asteroid 4227 Kaali is named after it (there is no connection between this asteroid and the crater).

References

• Tiirmaa, R. (1992). "Kaali Craters of Estonia and Their Meteoritic Material". Meteoritics. 27 (3): 297. Bibcode:1992Metic..27Q.297T.
• Anto Raukas, J.-M. Punning, T. Moora, Ü. Kestlane, A. Kraut (2005). "The Structure and Age of the Kaali Main Crater, Island of Saaremaa, Estonia". Impact Studies (2): 341–355. doi:10.1007/3-540-27548-7_13.{{cite journal}}: CS1 maint: multiple names: authors list (link)

External links

• Kaali crater home page
• About Kaali crater on the official Saaremaa website
• Photos of the Kaali crater
• Impact tectonics