There is a crater lake on Hallasan called Baengnokdam (/), meaning white deer lake. It is formed by the collapse of the top of the ridge by the movement of magma underground. There is a legend attributing the name of the lake to otherworldly men who descend from heaven to play with white deer. Depending on the season, the circumference of the lake is up to 2 kilometers with a depth up to about 100 meters.