Zaō Onsen (蔵王温泉) is a famous hot spring area on Mount Zaō in the northern part of Honshū, the main island of Japan.

The hot mineral water has a high acid and sulfur content,[1] giving it the characteristic smell of rotten eggs from the sulphur.

Other minerals include iron, aluminum, sulfate and chloride.

[5] The Zao Mountain is known for its conifer trees which become encrusted and solidified by January due to the hard rime phenomenon, which is caused by heavy snow and winds of freezing temperatures.

[6] They are caused by the frigid storm winds of the Siberian jet stream.