Lake_Superior - Wikiparency

# Lake Superior Lake Superior is the largest freshwater lake on Earth by surface area — 82,100 km², holding ≈12,100 km³ of [[Water]], roughly one-tenth of the planet's unfrozen surface fresh water — and the cold headpiece of the Great Lakes chain shared by [[Minnesota]], Wisconsin, Michigan, and Ontario. Its surface sits at 183 m; its deepest sounding, 406 m, puts the floor 223 m below sea level. For this vault the lake is the receiving basin of the entire [[WT!Minnesota_Great_Lakes_Basin]]: the [[St._Louis_River]] and several dozen short North Shore streams — [[Lester_River]], [[Knife_River]], [[Gooseberry_River]], [[Baptism_River]], [[Temperance_River]], [[Brule_River]], [[Pigeon_River]] and kin — end here, dropping off the rim of an ancient rift onto the coldest, clearest shelf of the Great Lakes. Everything distinctive about it — 191-year retention, reluctant stratification, November storm seas — follows from one fact: an enormous volume of nearly 4 °C water in a mid-continental climate. ## The numbers of a cold inland sea Superior is 563 km long and up to 257 km wide, with about 4,390 km of shoreline including islands; mean depth is 147 m, an order of magnitude beyond the other Great Lakes' shallower basins. Inflow arrives from roughly 200 tributaries — the largest overall is Ontario's Nipigon, the largest on the U.S. side the [[St._Louis_River]] — yet the sole outlet, the St. Marys River at Sault Ste. Marie, carries only ≈2,000 m³/s on average. Volume divided by outflow gives the hydraulic retention time: about 191 years, so the lake integrates two centuries of its watershed's chemistry. That watershed is small relative to the lake (≈128,000 km² of land), which is why Superior stays oligotrophic and transparent: most of its water budget is precipitation onto, and evaporation off, the surface itself, with river loads — the [[Nemadji_River]]'s red clay excepted — quickly diluted. ## A rift basin full of meltwater The hole itself is not glacial in origin. About 1.1 billion years ago the Midcontinent Rift tried to split North America, flooding the region with basalt (the North Shore Volcanic Group) and intruding the Duluth gabbro; the failed rift's subsided axis, softer sedimentary fill, left a trough in the [[Crust_(geology)]] that Pleistocene ice lobes later gouged clean. As the last lobe retreated, proglacial stages such as Glacial Lake Duluth stood tens of meters above today's shore — their beach terraces are still legible on the hillside above Duluth — before lower outlets opened. Isostatic rebound continues: the land at the outlet is rising faster than the southwestern end, slowly tilting the basin and drowning river mouths like the [[St._Louis_River]]'s, whose estuary hosts the Duluth–Superior harbor. The same tilted rift-edge [[Geomorphology]] gives every Minnesota tributary from the [[Split_Rock_River]] to the [[Devil_Track_River]] its staircase of falls and gorges. ## Thermal behavior: dimictic, barely Superior is dimictic — it mixes top to bottom twice a year — but its heat capacity makes both cycles grudging. Below the thermocline the water sits near 3.98 °C, the temperature at which [[Water]] reaches maximum [[Density]]; spring warming therefore proceeds by a migrating "thermal bar" of 4 °C water that separates stratified nearshore zones from the still-mixing interior. Offshore stratification often waits until July, and the summer epilimnion stays thin and cool, though surface temperatures have risen markedly since 1980, among the fastest warming trends of any large lake. Complete winter ice cover is rare — a handful of seasons per century, 2014 being a recent near-total year — because so much stored heat must be shed first ([[Heat_transfer]] across the air–lake interface lags the [[Atmosphere_of_Earth]]'s seasonal swing by weeks). The lake air-conditions its coast: North Shore summers run cooler and winters milder than inland [[Minnesota]], while south-shore snowbelts collect meters of lake-effect snow. ## The North Shore tributaries The Minnesota shore from Duluth to the border [[Pigeon_River]] receives a fleet of short, steep, flashy streams that this vault documents individually: [[Lester_River]], [[French_River]], [[Little_Sucker_River]], [[Knife_River]], [[Stewart_River]], [[Encampment_River]], [[Gooseberry_River]], [[Split_Rock_River]], [[Beaver_River]], [[Baptism_River]], [[Little_Marais_River]], [[Manitou_River]], [[Caribou_River]], [[Two_Island_River]], [[Cross_River]], [[Temperance_River]], [[Onion_River]], [[Poplar_River]], [[Cascade_River]], [[Devil_Track_River]], [[Kimball_Creek]], [[Kadunce_River]], [[Brule_River]], [[Flute_Reed_River]], and [[Reservation_River]]. Their basins are small and bedrock-floored, so discharge spikes within hours of rain and shrinks to a trickle by late summer; several ([[Knife_River]] notably) are managed for steelhead runs limited by exactly that flashiness. The [[Temperance_River]] owes its name to a joke — it reaches the lake without a "bar" at its mouth. Behind them, the larger [[Cloquet_River]] and [[Whiteface_River]] feed the [[St._Louis_River]] rather than the shore directly. ## Navigation, storms, wrecks Commerce has run through the Soo Locks since 1855, letting 300 m lakers lift 8 m from Huron to Superior and carry taconite from the [[Iron_ore]] docks of Duluth, Two Harbors, and Silver Bay, plus grain and coal — the cargo base that made Duluth, ≈3,770 km of navigation from the Atlantic, a deep-sea port. The cost is exposure: with over 500 km of fetch, autumn extratropical cyclones (the "witch of November") raise seas above 8 m. The Mataafa storm of November 1905 wrecked or damaged some 29 vessels; the SS Edmund Fitzgerald went down with all 29 hands on November 10, 1975. A [[Wave]] field with that fetch, plus water that stays lethally cold in every month, explains the lake's reputation for keeping its dead. Modern [[Weather_forecasting]] and gale warnings have made losses rare, but the physics has not changed. **On the spine:** [[Minnesota]] · [[St._Louis_River]] · [[Temperance_River]] · [[Water]] · [[WT!Minnesota_Great_Lakes_Basin]].  **Part of the [[WT!Thury_Hydrodynamics_Compendium|Thury Hydrodynamics Compendium]]** — main article for section 20, *Lake Superior*. Related sections: [[Hydrostatics]] · [[Geophysical_fluid_dynamics]] · [[Hydrology]] · [[Wind_wave]].   **Microsim — three.js (Wikitube framework):** *Lake Superior* <div class="wt-sim" data-src="https://wikitube-3d-microsims.netlify.app/thury/Lake_Superior.html" data-title="Lake Superior"></div> *Built from `MICROSIM_GUIDE/specs/sims/Lake_Superior.json`; part of the [[WT!Thury_Hydrodynamics_Compendium|Thury Hydrodynamics Compendium]] set.*  ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Lake_Superior) : [Wikitube](https://en.wikitube.io/wiki/Lake_Superior) ## Previous hub tags Hubs: —. Portals: [[PORTAL_WT!Thury_Hydrodynamics_Compendium]]. --- *Repopulated 2026-08-12 · redlink fill · 0 deletions.*