One of the most unique
hot springs in the world

A special high-alkaline hot spring borne out of the
serpentine rock layer that forms the geology of the Happo-one area.

The special &
unique hot springs of
Hakuba Happo Onsen

Hakuba Happo Onsen image

Hakuba Happo Onsen
A hot spring resort area located in the heart of Hakuba Valley, Nagano.

Hakuba Happo Onsen is a hot spring area located at the foot of Happo-one, in the western part of Hakuba Village in Nagano. The summit of Mt. Hakuba Yarigatake (2,903m) in the Northern Alps looms nearby, providing a spectacular backdrop for the region.
The hot spring supply combines water from the well #1 and the well #3, and provides water to 4 bath houses, around 65 accommodation facilities, and 3 footbaths.
The spring water has an extremely high hydrogen-ion concentration (pH) of 11.2, and can reach temperatures as high as 49.7°C. It is classified as an simple alkaline hot spring (alkaline hypotonic hot spring).

Illustrated Map of Hakuba Onsen

Hot Springs that Attract Scientists from Around the World

As the hot spring water passes over the serpentine rocks that make up the geology of the Hakuba Happo Onsen area, a reaction produces spring water that is highly alkaline and that contains a very high hydrogen content, as well as hydrocarbons such as methane, which are the basis of life. It is believed that the water quality is the same as that which existed four billion years ago, when life first emerged on Earth. To that end, it is attracting attention from researchers around the world who are trying to understand the beginnings of life on Early Earth.

Hot Springs that Attract Scientists from Around the World

Hakuba Happo Onsen,
Serpentine Rock & Natural Hydrogen


Happo-one is located on the western edge of the Fossa Magna on the Itoigawa-Shizuoka Tectonic Line, and is a rare place in Japan where serpentine rocks are exposed above ground.
These serpentine rocks called jamongan react with hydrothermal water to produce the hot spring water at Hakuba Happo Onsen, and when the Earth–Life Science team from the Tokyo Institute of Technology analyzed samples of the hot spring, they found that the concentration of dissolved hydrogen in the area near the source far exceeded levels normally found elsewhere.
Moreover, after observing natural hydrogen at the Obinata-no-Yu and Happo-no-Yu open-air baths, they also announced that it is the only natural hydrogen hot spring area in Japan.

Hot Spring Analysis Report

Spring Water Temperature
49.7℃(42°C or higher at the spring water gushing point is considered a "high-temperature spring")
Hydrogen ion concentration
11.2 (at time of collection) 11.6 (at time of analysis)
Classified as an Alkaline Spring, due to a high pH over 10(the sensation of the hot water varies slightly by bathing facility, depending on the distance from the spring's gushing point)
Mineral Content
“Simple Hot Spring” due to less than 1,000 mg of dissolved mineral content per 1 kg of water, and also “Hypotonic” due to less than 8,000 mg of dissolved mineral content per 1 kg of water.
(Hot spring water that is less mineralized than the skin is classified as “hypotonic”, whilst water that is similar is “isotonic”, and water that is more mineralized is “hypertonic”)

*Based on these characteristics, Hakuba Happo Onsen is classified as an "alkaline simple hot spring"(alkaline hypotonic hot spring).

Hot Spring Water Supply
to Lodging Facilities

Hakuba Happo onsen spring source

Happo-one Kaihatsu owns the Hakuba Happo onsen spring source and supplies hot spring water to approximately 80 facilities in the Happo area.

List of facilities supplied with hot spring water

A single hot spring can supply over 80 facilities!


①世界的にも珍しい個性豊かな温泉 ②蛇紋岩が生んだ白馬八方温泉の奇跡 ③白馬八方温泉の歴史