earth science

Lake Mashū

Lake Mashū is a earth science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Lake Mashū rather than just read about it. In short: Lake Mashū (摩周湖, Mashū-ko) (Ainu: Kamuy-to) is an endorheic 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.

Key takeaways

Lake Mashū belongs to earth science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Lake Mashū to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Lake Mashū from memory before moving on to harder problems.

Reference excerpt

Lake Mashū (摩周湖, Mashū-ko) (Ainu: Kamuy-to) is an endorheic 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 lake in the world.

Hydrology

Lake Mashū is surrounded by steep crater walls 200 metres (660 ft) 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 41.6 metres (136 ft). Around the same time Lake Baikal was measured 40.5 metres (133 ft). 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 20 and 30 metres (66 and 98 ft). The loss in transparency is probably due to the introduction of sockeye salmon and rainbow trout into the lake and landslides. 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 Lake Mashin (魔神湖, Mashin-ko) by the Japanese. Over time, however, the Japanese began to refer to the lake by the Japanese reading for the neighboring peak, Mount Mashū (摩周岳, Mashū-dake). The kanji 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, 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 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 which rises from the middle of the lake, is one. The other is Mount Kamui, a stratovolcano with lava dome, 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 and dacite. The rock is non-alkali pyroclastic flow or mafic rock, dating from the Late Pleistocene to the Holocene. Some rock around the Mashū crater and Mount Nishibetsu is older still, dating from the Middle Pleistocene. 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 and rainbow trout 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.

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

In popular culture Sendoff Spring in Pokémon Diamond and Pearl and Pokémon Platinum is based on this lake as the Sinnoh region is a fictionalized version of Hokkaido.

See also Tourism in Japan List of lakes in Japan

References

External links

Mashu - Japan Meteorological Agency (in Japanese) "Mashu: National catalogue of the active volcanoes in Japan" (PDF). - Japan Meteorological Agency Mashu - Geological Survey of Japan Mashu: Global Volcanism Program - Smithsonian Institution Teshikaga navi - Teshikaga Town

Illustrations

Worked examples

Example 1 — a first encounter with Lake Mashū

Start with the simplest possible case. Write down what Lake Mashū claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In earth science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Lake Mashū before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Lake Mashū ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Lake Mashū

In research: Lake Mashū appears in earth science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Lake Mashū in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Lake Mashū is common in secondary-school and first-year university syllabi. It links to neighbouring topics Calderas of Hokkaido, Endorheic lakes of Asia, Hokkaido Heritage, so understanding it makes those chapters shorter.
In everyday life: Look for Lake Mashū outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Lake Mashū in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Lake Mashū means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Lake Mashū out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Lake Mashū in simple terms?

Why does Lake Mashū matter?

Because it connects several earth science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Lake Mashū?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Lake Mashū.