is a

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcano eruption. When large volumes of magma are erupted over a short time, structural support for the rock above the magma chamber is ...

lake A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...

in the city of Semboku, Akita Prefecture, northern Japan. It is the deepest lake in Japan at . The area is a popular vacation area and several hot spring resorts can be found in the hills above the lake. Akita Prefecture's largest ski area, Tazawako Ski Area a overlooks the lake.

Hydrology

Lake Tazawa has a surface elevation of 249 meters, and its deepest point is 174.4 meters below sea level. Due to this depth, there is no possibility that the lake is frozen in the dead of winter. At , it is slightly deeper than

Lake Shikotsu is a caldera lake in Chitose, Hokkaidō, Japan. It is a part of the Shikotsu-Toya National Park. Geography Lake Shikotsu is located in the south-west part of Hokkaidō. It has an average depth of and a maximum depth of , making it the seco ...

in Hokkaidō (423.4 meters), and is the 17th deepest lake in the world. Lake Tazawa has no natural inflow or outflow, and in 1931, had a measured transparency of 31 meters, comparable with

Lake Mashū (Ainu language, Ainu: Kamuy-to) is an endorheic Volcanic crater lake, crater lake formed in the caldera of a potentially active volcano. It is located in Akan Mashu National Park on the island of Hokkaido, Japan. It has been called the clearest ...

, but with abundant aquatic organisms. However, due to the construction of

hydroelectric power plant Hydroelectricity, or hydroelectric power, is electricity generated from hydropower (water power). Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other renewable sources combined an ...

facilities and agricultural runoff, coupled with an influx of highly acidic water from

Tamagawa Hot Spring is a hot spring located in the city of Semboku, Akita in northern Japan. Water profile The spring has a flow of 9000 liters/minute and feeds a 3-meter wide stream with a temperature of 98 °C. The water from Tamagawa Hot Spring is extre ...

, transparency has been reduced to less than 4 meters, and by the late 1940s the lake had become so acidic (pH 4.3) that it could no longer support irrigated agriculture. Starting in 1972, the Japanese government has been attempting to rectify the acidity problem through introduction of

lime Lime commonly refers to: * Lime (fruit), a green citrus fruit * Lime (material), inorganic materials containing calcium, usually calcium oxide or calcium hydroxide * Lime (color), a color between yellow and green Lime may also refer to: Botany ...

, with a new facility completed in 1991. However, in the year 2000, the lake still had an acidity of 5.14 at the 200 meter depth, and 4.91 at the 400 meter depth, indicating that full recovery has not yet been achieved.

Geology

Due to its extreme depth, and almost circular profile, Lake Tazawa was considered to be either a caldera lake caused by volcanic activity or a crater lake caused by a meteorite impact. The depth of the lake was first measured as 397 meters, using a hemp rope, by Japanese geologist Tanaka Akamaro in 1909. The Akita Prefectural Fisheries Experiment Station survey indicated a depth of 413 meters in 1926 using a wire rope. During a three-year survey from 1937 to 1940, geologist Yoshimura Nobuyoshi surveyed the lake bottom, finding the deepest point to be . The survey also found two small volcanic cones and sedimentation deposits to the depth of around one kilometer on the north-west side of the lake bottom. These findings lend credence to the theory that the lake is indeed of volcanic origin, from an explosive eruption of 1.4 million years ago.

Natural history

Prior to 1940, the main species of fish in Lake Tazawa included the indigenous ''kunimasu'' ('' Oncorhynchus nerka kawamurae''), Sockeye salmon, Japanese dace (genus ''

Tribolodon ''Tribolodon'' (Redfin dace) is a genus of cyprinid fishes found in marine biology, marine and freshwater in Eastern Asia. Species There are currently 4 recognized species in this genus: * ''Tribolodon brandtii'' (Benedykt Dybowski, Dybowski, 187 ...

''), Japanese trout, char, carp,

catfish Catfish (or catfishes; order Siluriformes or Nematognathi) are a diverse group of ray-finned fish. Named for their prominent barbels, which resemble a cat's whiskers, catfish range in size and behavior from the three largest species alive ...

and

eel Eels are ray-finned fish belonging to the order Anguilliformes (), which consists of eight suborders, 19 families, 111 genera, and about 800 species. Eels undergo considerable development from the early larval stage to the eventual adult stage ...

. However, after the acidic content of the lake changed in 1940, the only surviving fish is the dace, while most of the other species, including the ''kunimasu'', are thought to have gone extinct.

History

Lake Tazawa was named in the

Meiji period The is an era of Japanese history that extended from October 23, 1868 to July 30, 1912. The Meiji era was the first half of the Empire of Japan, when the Japanese people moved from being an isolated feudal society at risk of colonization ...

when its surrounding foothills were settled. However, the lake was known to the Ainu people, and the name “Tazawa” is thought to be derived from the Ainu language ''Tapukopu'' ("hill with a raised circular top") The lake is also connected with the legendary maiden of beauty, Tatsuko, itself of unknown origin. Tazawa has a bronze statue of Tatsuko near its shore. Tatsuko, wishing for undying youth and beauty, is said to have been turned into a lake-goddess. The statue of Tatsuko by

Yasutake Funakoshi was a Japanese sculptor and painter. Life and work Funakoshi was born in what is now the town of Ichinohe in the Iwate Prefecture in northern Honshū. Later he attended middle school in Morioka where the painter Shunsuke Matsumoto was a ...

stands with her back to the clear blue waters, a figure of pureness and beauty, and was unveiled on April 12, 1968.''Funakoshi Yasutake''
- website of the

Iwate Museum of Art The is an art museum An art museum or art gallery is a building or space for the display of art, usually from the museum's own collection. It might be in public or private ownership and may be accessible to all or have restrictions in place ...

(retrieved 2013-4-22)http://www.city.semboku.akita.jp/en/sightseeing/spot/04_tatsukozou.html (retrieved 2013-4-22)

Notes

References

*Likens, Gene. ''Lake Ecosystem Ecology: A Global Perspective''. Academic Press (2010) *Wilkening, Kenneth. ''Acid Rain Science and Politics in Japan: A History of Knowledge and'' Action. MIT Press (2004)

External links

*
Tazawa Ko Caldera
- Geological Survey of Japan

Tazawako Tourist Association
{{Authority control Tazawa Tazawa Tazawa Tourist attractions in Akita Prefecture Landforms of Akita Prefecture Semboku, Akita Pleistocene calderas Volcanoes of Honshū