( Ainu: Kamuy-to) is an

endorheic An endorheic basin ( ; also endoreic basin and endorreic basin) is a drainage basin that normally retains water and allows no outflow to other external bodies of water (e.g. rivers and oceans); instead, the water drainage flows into permanent ...

crater lake formed in the

caldera A caldera ( ) is a large cauldron-like hollow that forms shortly after the emptying of a magma chamber in a volcanic eruption. An eruption that ejects large volumes of magma over a short period of time can cause significant detriment to the str ...

of a potentially active volcano. It is located in Akan Mashu National Park on the island of

Hokkaido is the list of islands of Japan by area, second-largest island of Japan 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 fr ...

Japan Japan is an island country in East Asia. Located in the Pacific Ocean off the northeast coast of the Asia, Asian mainland, it is bordered on the west by the Sea of Japan and extends from the Sea of Okhotsk in the north to the East China Sea ...

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

Hydrology

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 is a rift lake and the deepest lake in the world. It is situated in southern Siberia, Russia between the Federal subjects of Russia, federal subjects of Irkutsk Oblast, Irkutsk Oblasts of Russia, Oblast to the northwest and the Repu ...

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 tributary, tributaries of the Pacific Ocean in North America and Asia. The steelhead (sometimes called steelhead trout) is an Fish migration#Classification, ...

into the lake and

landslides Landslides, also known as landslips, rockslips or rockslides, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, mudflows, shallow or deep-seated slope failures and debris flows. Landslide ...

.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 a person can see the surface of the lake, they will have bad luck.

Origin of the name

The origin of Lake Mashū's name is unclear. The lake's original Ainu name was Kintan-kamuy-to or ''lake of the mountain god''. Ainu language researcher Nagata Housei proposed that the Japanese name originated from the Ainu Mas-un-to or ''lake of the gulls.'' This was then 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 logographic Chinese characters, adapted from Chinese family of scripts, Chinese script, used in the writing of Japanese language, Japanese. They were made a major part of the Japanese writing system during the time of Old Japanese and are ...

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 in a shortened form, as Kamuyto or ''lake of the gods''.

Volcanic caldera

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 typically conical volcano built up by many alternating layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with ...

, 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 Plinian eruptions or Vesuvian eruptions are volcanic eruptions characterized by their similarity to the eruption of Mount Vesuvius in 79 AD, which destroyed the ancient Roman cities of Herculaneum and Pompeii. The eruption was described in a le ...

about 2,000 years ago that dropped

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

over the region. Mashū volcano is rated with a

Volcanic Explosivity Index The volcanic explosivity index (VEI) is a scale used to measure the size of explosive volcanic eruptions. It was devised by Christopher G. Newhall of the United States Geological Survey and Stephen Self in 1982. Volume of products, eruption c ...

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 predomina ...

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 rhyolite. ...

. 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 (geology), age in the international geologic timescale in chronostratigraphy, also known as the Upper Pleistocene from a Stratigraphy, stratigraphic perspective. It is intended to be the fourth division ...

to the

Holocene The Holocene () is the current geologic time scale, geological epoch, beginning approximately 11,700 years ago. It follows the Last Glacial Period, which concluded with the Holocene glacial retreat. The Holocene and the preceding Pleistocene to ...

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

Middle Pleistocene The Chibanian, more widely known as the Middle Pleistocene (its previous informal name), is an Age (geology), age in the international geologic timescale or a Stage (stratigraphy), stage in chronostratigraphy, being a division of the Pleistocen ...

. 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 ''Bosmina'' is a genus in the order Cladocera, the water fleas. Its members can be distinguished from those of ''Bosminopsis'' (the only other genus in the family Bosminidae) by the separation of the antenna (biology), antennae; in ''Bosminopsis' ...

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'' and '' Abies sachalinensis'' and birch forest with ''

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

''.

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 establi ...

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

In popular culture

Sendoff Spring in ''

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

'' and '' Pokémon Platinum'' 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 navi
- 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 Hokkaido Heritage