Changbai Mountain is a dormant volcano. It has been recorded that it erupted three times. When the volcano erupted and ejected a large amount of lava, the crater formed a basin. After a long time, water accumulated into lakes, it became the present Tianchi. Although Tianchi is surrounded by peaks, at an altitude of 2154 meters, it is oval in shape, 4.85 kilometers long in North and south, 3.35 kilometers wide in East and west, 9.82 square kilometers in area and 13.1 kilometers in circumference. The average depth is 204 meters and the deepest depth is 373 meters. It is the deepest lake in China, with a total water storage capacity of about 2 billion cubic meters. There are also many hot springs in Tianchi, forming several hot spring area. In the area about 150 meters long and 50 meters wide, the water temperature is maintained at 42 degrees centigrade all the year round. In the severe winter season, the hot springs are also steaming hot.