Kaali is a group of nine meteorite craters in the village of Kaali on the Estonian island of Saaremaa. Most recent estimates put its formation shortly after 1530–1450 BC. It was created by an impact event and is one of the fewimpact events that has occurred in a populated area. Before the 1930s there were several hypotheses 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, around 3,500 years ago. The estimates of the age of the Kaali impact structure provided by different authors vary by as much as 6,000 years, ranging from ~6,400 to ~400 years before current era. Analysis of silicate spherules in Estonian bogs show that the possible age of the impact craters could be approximately 7,600 years. A study based on elevated Ir signal in a nearby bog suggested much younger age of 4th century BC. The craters were formed by a meteor with an estimated impact velocity of between with a total mass of between 20 and 80 metric tonnes. According to some researchers the meteor arrived from the north-east. At an altitude of, the meteor broke into pieces and fell to the Earth in fragments, the greatest of which produced a crater with a diameter of and a depth of. The explosion removed approximately of dolomite and other rocks and formed a tall, extremely hot gas flow. Vegetation was incinerated up to from the impact site. Kaali Lake is on the bottom of this crater. Eight smaller craters are also associated with this bombardment. Their diameters range from and their respective depths vary from. They are all within of the main crater.
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 long, with a median width of about and an average height of. 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 heroes head in 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 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."
