In antiquity, Changbai Mountain was a volcano and history records three eruptions since the 16^th century. Violent eruptions left behind a huge crater n which, as time went by,  a lake was formed. The lava flows became 16 mountain peaks around the lake, seven of them within the Democratic People's Republic of Korea and nine in China. The Tianchi Lake is the largest volcano lake in China and also the source of the Songhua, Tumen and Yalu rivers. Its high altitude, 2,150 meters above sea level, gave rise to its name which translates as "Heavenly Pool".