Changbai Mountain Tianchi (Changbai mountain pool in the sky) is a dormant volcano, the crater water into a lake, the summer melt pool water is bluer than the sky; winter ice snow is as white as snow, surrounded by 16 peaks, only in the Tianhuo Peak and Longmen Peaks, there is a narrow pool water overflow, flying and falling white waterfall, is the main source of the Songhua River. Changbai Mountain was formed 12 million years ago in geological orogeny. After many eruptions, it became a giant umbrella body. When the volcano was dormant, the spring overflowed, forming a vast water surface of more than ten square kilometers. Tianchi is2189.1 meters above sea level, slightly elliptical,4.4 kilometers long from north to south,3.37 kilometers wide from east to west. The water catchment area is 21.4㎞ 2, the water surface area is 9.82㎞ 2, the surface circumference is 13.1 km, the average water depth is 204 meters, and the deepest reaches 373 meters. The total water storage capacity is 20.4 billion cubic meters. The water temperature in Tianchi is 0.7℃-11℃, and the average annual temperature is 7.3℃. Tianchi is like a magnificent jasper set in the majestic peaks of Changbai Mountain. It is the largest volcanic lake in China and the deepest alpine lake in the world. It is now the boundary lake between China and North Korea.