Introduction to the Landforms and Geology of Japan

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Goshogake and Tamagawa Hot Springs

The Goshogake and the Tamagawa hot springs are welling up in small areas where there are a few hotels. In much larger hot spring areas such as Atami, Kusatsu, and Beppu, there are more than 100 hotels (in Japan, hot springs are important resources for tourism). Nonetheless, the Goshogake and the Tamagawa hot springs possess unique features. These hot springs are at the flank of Akita-Yakeyama Volcano, Akita Prefecture, northern Honshu (Tohoku); the Goshogake hot springs are located in the eastern flank and the Tamagawa hot springs in the western flank. Characteristics of each spring are different despite the only 6.4-km distance between them. The Goshogake hot springs are famous for mud volcanoes. The Tamagawa hot springs are characterized by extremely strong acid hot water (pH 1.2, 97°C at the Obuki spring) with high flow rate gush and a rare mineral, hokutolite. I will introduce some features of these hot springs and also explain how to get there on the last page.

 

Akita-Yakeyama Volcano

Akita-Yakeyama Volcano (hereinafter “Yakeyama”) is in an active geothermal area called Hachimantai Geothermal Area. There are several active volcanoes including the Hachimantai, the Iwate, and the Komagatake volcanoes besides Yakeyama and geothermal power plants within a 13-km radius. Since these volcanoes except the Hachimantai volcano repeatedly erupted for the past 100 to 300 years, this area is one of the most active volcanic areas in Japan. The volcanic activity of Yakeyama started about 300 thousand years ago and formed the volcano by multiple eruptions. The last eruption (steam eruption) occurred on a small scale in 1997 and active fumaroles activity are seen in some places including the Tamagawa and the Goshogake areas at present. Yakeyama is a stratovolcano with the base of 7 km in diameter and the summit altitude of 1366 m, and has craters on the summit and flank. The extrusive rocks are andesite and dacite. Most lava and pyroclastic rocks are friable to produce forms of landslide (horseshoe-shaped depressions) because of hydrothermal alteration.
[Photos of Akita-Yakeyama in the website of Geological Survey of Japan]

Goshogake hot springs

In the Goshogake hot spring area to the 3.8-km east of the summit of Yakeyama, many vents on reddish-brown bare land are discharging thermal water and vapor, some of which gush over 90°C water. Mud volcanoes and mud pots characterize the Goshogake hot springs because the water and vapor come up with mud. Hot pools are also a distinguished geothermal manifestation.

Mud volcanoes and mud pots

Mud volcanoes and mud pots in the Goshogake hot springs are formed by which mud is spouted out on the surface by pressure of compressed vapor. The mud is composed of sulfur and iron sulfide, which are produced by interaction between vapor and ground water, and altered rock (clay).

Photo 1 shows the largest mud volcanoes in Japan (Odoro Kazan). The mud volcanoes of Odoro Kazan are in a old hot pool. The mud ejected from the bottom deposits and fills the pool. The mud of the most upper layer is hard and the older mud under the layer is squashy because of containing much water. The mud accumulated in the hot pool is brought up to the surface by rising geothermal water or vapor to form these mud volcanoes. Their formation started around 1917 to 1918. The height of the volcanoes is about 1 m. The mud layer in the hot pool is 8 m thick and the temperature of discharged materials is about 95°C.

 

 

 

Hot pool, Oyunuma
Oyunuma Photo 2: Oyunuma []
Toward the back of the photo is west.

 

A bar in Oyunuma Photo 3: Bar in Oyunuma []

Of the hot pools found in this area, the largest one is Oyunuma. This hot pool is the center of geothermal activity in the Goshogake hot springs at present, the surface area of which is 3000 m2. The depth is less than 5 m in the eastern part and more than 10 m in the western part. Oyunuma was formed by which hot pools were gathered together. Mud composed of altered rock (clay), sulfur, and iron sulfide have been depositing in the pool, producing a bar, mud volcanoes and mud pots. Because these mud structures are younger than those of Odoro Kazan, they are probably in the early stage of the formation. Hot water is intermittently forced out like a geyser in the pool. The water temperature is about 83°C at the surface and 118.2°C (max. in 1982 [Yuhara et al., 1985]) at the deepest part. The water contains sulfate, the pH of which is around 3. The discharge of hot water is 4000 kg/hour (90 to 95°C) at the eastern bottom and 9000 kg/hour (about 120°C [water vapor]) at the western bottom (Yuhara et al., 1985). The geothermal activity in the western part of Oyunama is more active than in the eastern part. Therefore, the hot pool is expanding toward the west. The center of the activity in Goshogake is moving westward. Odoro Kazan to the east of Oyunuma was the formerly heart of the activity.

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