(

Ainu Ainu or Aynu may refer to: *Ainu people, an East Asian ethnic group of Japan and the Russian Far East *Ainu languages, a family of languages **Ainu language of Hokkaido **Kuril Ainu language, extinct language of the Kuril Islands **Sakhalin Ainu la ...

: Kamuy-to) is an

endorheic An endorheic basin (; also spelled endoreic basin or endorreic basin) is a drainage basin that normally retains water and allows no outflow to other external bodies of water, such as rivers or oceans, but drainage converges instead into lakes ...

crater lake Crater Lake ( Klamath: ''Giiwas'') is a volcanic crater lake in south-central Oregon in the western United States. It is the main feature of Crater Lake National Park and is famous for its deep blue color and water clarity. The lake partly fill ...

formed in the

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 ...

of a potentially active volcano. It is located in

Akan Mashu National Park is a national park located on the island of Hokkaidō, Japan. Along with Daisetsuzan National Park, these are the two oldest national parks in Hokkaidō. The park was established December 4, 1934. Akan is an area of volcanic craters and for ...

on the island of

Hokkaido is Japan, Japan's Japanese archipelago, second largest island and comprises the largest and northernmost Prefectures of Japan, prefecture, making up its own List of regions of Japan, region. The Tsugaru Strait separates Hokkaidō from Honshu; th ...

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 n ...

. It has been called the clearest lake in the world.

Hydrology

Kamui-nupuri and mashu-dake on hokkaido map

Lake Mashū is surrounded by steep crater walls high. It has no significant inlets and no outlet. The lake is one of the clearest in the world and one of the deepest in Japan. On August 1, 1931, the transparency of the water was measured at . Around the same time

Lake Baikal Lake Baikal (, russian: Oзеро Байкал, Ozero Baykal ); mn, Байгал нуур, Baigal nuur) is a rift lake in Russia. It is situated in southern Siberia, between the federal subjects of Irkutsk Oblast to the northwest and the ...

was measured . This is the basis for the lake's claim to be the clearest in the world. Since the 1950s the transparency has tended to range between . The loss in transparency is probably due to the introduction of

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 ...

and

rainbow trout The rainbow trout (''Oncorhynchus mykiss'') is a species of trout native to cold-water tributaries of the Pacific Ocean in Asia and North America. The steelhead (sometimes called "steelhead trout") is an anadromous (sea-run) form of the coast ...

into the lake and

landslides Landslides, also known as landslips, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, deep-seated slope failures, mudflows, and debris flows. Landslides occur in a variety of environme ...

.NHK World HD Channel At the same time, the clarity of Lake Baikal has not been measured. In summer, the surface of Lake Mashū is often obscured by fog. There is usually fog covering around the lake for about 100 days of the year. This has given the lake a reputation for mysteriousness. A local legend says that if you can see the surface of the lake, you will have bad luck.

Origin of the name

Lake Mashū was originally named ''Lake of the Devil'' by the

. This was rendered as by the Japanese. Over time, however, the Japanese began to refer to the lake by the Japanese reading for the neighboring peak, ., , page 128, (in Japanese). The

kanji are the logographic Chinese characters taken from the Chinese script and used in the writing of Japanese. They were made a major part of the Japanese writing system during the time of Old Japanese and are still used, along with the subsequ ...

for this peak translate roughly as ''scrubbed area mountain''. The Ainu name for this peak, by which it is commonly known today, is Kamuinupuri or ''mountain of the gods''. The lake also retains its Ainu name, Kamuito or ''lake of the gods''.

Volcanic caldera

Kussharo Caldera & Mashu Caldera Relief Map, SRTM-1

Mashū formed less than 32,000 years ago. The caldera is the remains of a

stratovolcano A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and peri ...

, which is actually a parasitic cone of the larger Lake Kussharo caldera. The eruption that created the current caldera occurred around 7,000 years ago. The last eruption was a plinian eruption about 2,000 years ago that dropped

pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough-textured volcanic glass, which may or may not contain crystals. It is typically light-colored. Scoria is another vesicular v ...

over the region. Mashū volcano is rated with a Volcanic Explosivity Index of 6, the third highest among large volcanoes. Two volcanoes have grown out of the Mashū caldera. Kamuishu Island, a

lava dome In volcanology, a lava dome is a circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano. Dome-building eruptions are common, particularly in convergent plate boundary settings. Around 6% of eruptions ...

which rises from the middle of the lake, is one. The other is Mount Kamui, a stratovolcano with

, which forms the highest point on the eastern shore. A third volcano neighbors Kamuinupuri. It is Mount Nishibetsu. Mount Nishibetsu probably predates the caldera. The main rock type of the volcanoes is

andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predo ...

and

dacite Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained ( aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyo ...

. The rock is non-alkali

pyroclastic flow A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) is a fast-moving current of hot gas and volcanic matter (collectively known as tephra) that flows along the ground away from a volcano at average speeds of b ...

or mafic rock, dating from the

Late Pleistocene The Late Pleistocene is an unofficial age in the international geologic timescale in chronostratigraphy, also known as Upper Pleistocene from a stratigraphic perspective. It is intended to be the fourth division of the Pleistocene Epoch withi ...

to the

Holocene The Holocene ( ) is the current geological epoch. It began approximately 11,650 cal years Before Present (), after the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene togeth ...

. Some rock around the Mashū crater and Mount Nishibetsu is older still, dating from the

Middle Pleistocene The Chibanian, widely known by its previous designation of Middle Pleistocene, is an age in the international geologic timescale or a stage in chronostratigraphy, being a division of the Pleistocene Epoch within the ongoing Quaternary Period. Th ...

. The following table lists the eruptions of the Mashū volcano and Kamuinupuri.

Flora and fauna

The lake is inhabited by phytoplankton and zooplankton. * ''Melosira'' spp. * ''Synedra'' sp. * '' Daphnia longispina'' * '' Bosmina coregoni''

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 ...

and

have been introduced to the lake. On the slopes around and above the lake grow a mixture of evergreen forest with ''

Picea jezoensis ''Picea jezoensis'' (sometimes misspelled ''Picea yezoensis''), the dark-bark spruce, Ezo spruce, Yezo spruce, or Jezo spruce, is a large evergreen tree growing to 30–50 m tall and with a trunk diameter of up to 2 m. It is native to northeast ...

'' and ''

Abies sachalinensis ''Abies sachalinensis'', the Sakhalin fir, is a species of conifer in the family Pinaceae. It is found in Sakhalin island and southern Kurils (Russia), and also in northern Hokkaido (Japan). The first discovery by a European was by Carl Friedr ...

'' and birch forest with ''

Betula ermanii ''Betula ermanii'', or Erman's birch, is a species of birch tree belonging to the family Betulaceae. It is an extremely variable species and can be found in Northeast China, Korea, Japan, and Russian Far East (Kuril Islands, Sakhalin, Kam ...

''.

Economy

The Mashu-dake Hiking Course is a trail that goes along the crater rim and to the top of Mount Mashū. The trail leads through forest and grassland for about seven kilometers and takes about 2.5 to 3 hours to hike one way. There are no settlements along the shores of the lake. Access to the lakeshore itself is prohibited by the

Ministry of the Environment (Japan) The is a Cabinet-level ministry of the government of Japan responsible for global environmental conservation, pollution control, and nature conservation. The ministry was formed in 2001 from the sub-cabinet level Environmental Agency establishe ...

. Visitors may only view the lake from the designated observation towers.

In popular culture

Sendoff Spring in ''

Pokémon Diamond and Pearl and are 2006 role-playing video games developed by Game Freak, published by The Pokémon Company and Nintendo for the Nintendo DS. They are the first installments in the fourth generation of the ''Pokémon'' video game series. They were f ...

'' and ''

Pokémon Platinum is a 2008 role-playing video game developed by Game Freak, published by The Pokémon Company and Nintendo for the Nintendo DS handheld game console. It is an enhanced version of Pokémon Diamond and Pearl, ''Pokémon Diamond'' and ''Pearl'' and ...

'' is based on this lake as the Sinnoh region is a fictionalized version of Hokkaido.

References

External links

Mashu
- Japan Meteorological Agency * - Japan Meteorological Agency

- Geological Survey of Japan
Mashu: Global Volcanism Program
- Smithsonian Institution

- Teshikaga Town {{DEFAULTSORT:Mashu Calderas of Hokkaido Endorheic lakes of Asia Volcanic crater lakes Lakes of Hokkaido Volcanoes of Hokkaido VEI-6 volcanoes Holocene calderas Potentially active volcanoes Parasitic cones