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 (3237+/-10 14C yr BP). It was created by an impact event and is one of the few impact events that has occurred in a populated area (other ones are: Henbury craters and Carancas crater). 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 (Saaremaa Island, Estonia) provided by different authors vary by as much as 6,000 years, ranging from ~6,400 to ~400 years before current era (BCE). 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 iridium signal in a nearby bog suggested the 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. Effects According to the theory of more recent impact, Estonia at the time of impact 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 radius. In mythology Scholars, such as Karl Kello, maintain that the event figured prominently in regional mythology. It was, and still is, considered