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 in the city of Semboku,

Akita Prefecture is a Prefectures of Japan, prefecture of Japan located in the Tōhoku region of Honshu.Nussbaum, Louis-Frédéric. (2005). "Provinces and prefectures" in ; "Tōhoku" in . Its population is approximately 966,000 (as of 1 October 2019) and its ge ...

, northern

Japan Japan ( ja, 日本, or , and formally , ''Nihonkoku'') is an island country in East Asia. It is situated in the northwest Pacific Ocean, and is bordered on the west by the Sea of Japan, while extending from the Sea of Okhotsk in the north ...

. 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 is a caldera lake 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' ...

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 in

Hokkaidō is Japan's second largest island and comprises the largest and northernmost prefecture, making up its own region. The Tsugaru Strait separates Hokkaidō from Honshu; the two islands are connected by the undersea railway Seikan Tunnel. The la ...

(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, but with abundant aquatic organisms. However, due to the construction of hydroelectric power plant facilities and agricultural runoff, coupled with an influx of highly acidic water from Tamagawa Hot Spring, 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, 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 Black kokanee (''Oncorhynchus kawamurae''), or in Japanese language, Japanese, is a species of landlocked Oncorhynchus, Pacific trout in Japan that was thought to be extinct for 70 years before being rediscovered in 2010. The species was origina ...

''),

Sockeye salmon The sockeye salmon (''Oncorhynchus nerka''), also called red salmon, kokanee salmon, blueback salmon, or simply sockeye, is an anadromous species of salmon found in the Northern Pacific Ocean and rivers discharging into it. This species is a P ...

, Japanese dace (genus '' Tribolodon''), Japanese trout,

char Char may refer to: People *Char Fontane, American actress *Char Margolis, American spiritualist * René Char (1907–1988), French poet *The Char family of Colombia: ** Fuad Char, Colombian senator ** Alejandro Char Chaljub, mayor of Barranquilla ...

carp Carp are various species of oily freshwater fish from the family Cyprinidae, a very large group of fish native to Europe and Asia. While carp is consumed in many parts of the world, they are generally considered an invasive species in parts of ...

, catfish and eel. 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 when its surrounding foothills were settled. However, the lake was known to the

Ainu people The Ainu are the indigenous people of the lands surrounding the Sea of Okhotsk, including Hokkaido Island, Northeast Honshu Island, Sakhalin Island, the Kuril Islands, the Kamchatka Peninsula and Khabarovsk Krai, before the arrival of the Y ...

, and the name “Tazawa” is thought to be derived from the

Ainu language Ainu (, ), or more precisely Hokkaido Ainu, is a language spoken by a few elderly members of the Ainu people on the northern Japanese island of Hokkaido. It is a member of the Ainu language family, itself considered a language family isolate ...

''Tapukopu'' ("hill with a raised circular top") The lake is also connected with the legendary maiden of beauty,

Tatsuko Tatsuko (written: 立子, 竜子 or たつ子) is a feminine Japanese given name. Notable people with the name include: *, Japanese poet *, Japanese noble *, Japanese golfer See also *Tatsuko (mythology) Tatsuko (written: 立子, 竜子 or た� ...

, 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 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 (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