At the top of the Hallasan volcano, in the crater, there is Lake Baengnokdam, which expands and evaporates depending on rainfall.

It can reach a diameter of 2 kilometers and a depth of up to 100 meters. The slopes of Hallasan are covered with many smaller cones that once released lava and pyroclastic material. Such small cones on the slopes of a large volcano are called parasitic cones.