Lake Superior
Lake Superior is a lake in central North America. The northernmost, westernmost, and highest of the Great Lakes, Lake Superior straddles the Canada–United States border with the Canadian province of Ontario to the north and east and the U.S. states of Minnesota to the west and Michigan and Wisconsin to the south. It is the largest freshwater lake in the world by surface area and the third-largest freshwater lake by volume. It drains into Lake Huron via St. Marys River, then through the lower Great Lakes to the St. Lawrence River and ultimately the Atlantic Ocean.
Name
The Ojibwe name for the lake is gichi-gami, meaning "great sea". Henry Wadsworth Longfellow wrote this name as "Gitche Gumee" in the poem The Song of Hiawatha, as did Gordon Lightfoot in his song "The Wreck of the Edmund Fitzgerald.According to other sources, the full Ojibwe name is ᐅᒋᑉᐧᐁ ᑭᒋᑲᒥ Ojibwe Gichigami or ᐊᓂᐦᔑᓈᐯ ᑭᒋᑲᒥ Anishinaabe Gichigami. The 1853 dictionary by Father Frederic Baraga, the first one written for the Ojibway language, gives the Ojibwe name as Otchipwe-kitchi-gami.
In the 17th century, the first French explorers approached the great inland sea by way of the Ottawa River and Lake Huron; they referred to their discovery as le lac supérieur. Some 17th-century Jesuit missionaries referred to it as Lac Tracy. After taking control of the region from the French in the 1760s, following their defeat in the French and Indian War, the British anglicized the lake's name to Superior, "on account of its being superior in magnitude to any of the lakes on that vast continent".
Hydrography
Lake Superior empties into Lake Huron via the St. Marys River and the Soo Locks. Lake Superior is the largest freshwater lake in the world by area and the third largest in volume, behind Lake Baikal in Siberia and Lake Tanganyika in East Africa. The Caspian Sea, while larger than Lake Superior in both surface area and volume, is brackish.Lake Superior has a surface area of, which is approximately the size of South Carolina or Austria. It has a maximum length of and maximum breadth of. Its average depth is with a maximum depth of. Lake Superior contains 2,900 cubic miles of water. There is enough water in Lake Superior to cover the entire land mass of North and South America to a depth of. The shoreline of the lake stretches . The lake boasts a very small ratio of catchment area to surface area, which indicates minimal terrestrial influence.
American limnologist J. Val Klump was the first person to reach the lowest depth of Lake Superior on July 30, 1985, as part of a scientific expedition, which at 122 fathoms 1 foot below sea level is the second-lowest spot in the continental interior of the United States and the third-lowest spot in the interior of the North American continent after Great Slave Lake in the Northwest Territories of Canada and Iliamna Lake in Alaska.
While the temperature of the surface of Lake Superior varies seasonally, the temperature below is an almost constant. This variation in temperature makes the lake seasonally stratified. Twice per year, however, the water column reaches a uniform temperature of from top to bottom, and the lake waters thoroughly mix. This feature makes the lake dimictic. Because of its volume, Lake Superior has a retention time of 191 years.
Annual storms on Lake Superior regularly feature wave heights of over. Waves well over have been recorded.
Tributaries
Lake Superior is fed by more than 200 rivers, including the Nipigon River, the St. Louis River, the Pigeon River, the Pic River, the White River, the Michipicoten River, the Bois Brule River and the Kaministiquia River. The lake's outlet at St. Marys River has a relatively steep gradient with rapids. The Soo Locks enable ships to bypass the rapids and to overcome the height difference between Lakes Superior and Huron.Water levels
The lake's average surface elevation is above sea level. Until approximately 1887, the natural hydraulic conveyance through the St. Marys River rapids determined the outflow from Lake Superior. By 1921, development in support of transportation and hydroelectric power resulted in gates, locks, power canals and other control structures completely spanning St. Marys rapids. The regulating structure is known as the Compensating Works and is operated according to a regulation plan known as Plan 1977-A. Water levels, including diversions of water from the Hudson Bay watershed, are regulated by the International Lake Superior Board of Control, which was established in 1914 by the International Joint Commission.Lake Superior's water level was at a new record low in September 2007, slightly less than the previous record low in 1926. Water levels recovered within a few days.
The lake's water level fluctuates from month to month, with the highest lake levels in October and November. The normal high-water mark is above the datum. In the summer of 1985, Lake Superior reached its highest recorded level at above the datum. 2019 and 2020 set new high-water records in nearly every month.
The lake's lowest levels occur in March and April. The normal low-water mark is below the datum. In the winter of 1926, Lake Superior reached its lowest recorded level at below the datum. Additionally, the entire first half of the year included record low months. The low water was a continuation of the dropping lake levels from the previous year, 1925, which set low-water records for October through December. During the nine-month period of October 1925 to June 1926, water levels ranged from below Chart Datum. In the summer of 2007 monthly historic lows were set; August at, and September at.
Climate change
According to a study by professors at the University of Minnesota Duluth, Lake Superior may have warmed faster than its surrounding area. Summer surface temperatures in the lake appeared to have increased by about between 1979 and 2007, compared with an approximately increase in the surrounding average air temperature. The increase in the lake's surface temperature may be related to the decreasing ice cover. Less winter ice cover allows more solar radiation to penetrate and warm the water. If trends continue, Lake Superior, which freezes over completely once every 20 years, could routinely be ice-free by 2040 although more current data through 2021 does not support this trend.Warmer temperatures could lead to more snow in the lake effect snow belts along the shores of the lake, especially in the Upper Peninsula of Michigan. Two recent consecutive winters brought high ice coverage to the Great Lakes, and on March 6, 2014, overall ice coverage peaked at 92.5%, the second-highest in recorded history. Lake Superior's ice coverage further beat 2014's record in 2019, reaching 95% coverage.
Geography
The largest island in Lake Superior is Isle Royale in Michigan. Isle Royale contains several lakes, some of which also contain islands. Other well-known islands include Madeline Island in Wisconsin, Michipicoten Island in Ontario, and Grand Island in Michigan.The larger cities on Lake Superior include the twin ports of Duluth, Minnesota, and Superior, Wisconsin; Thunder Bay, Ontario; Marquette, Michigan; and the twin cities of Sault Ste. Marie, Michigan, and Sault Ste. Marie, Ontario. Duluth-Superior, at the western end of Lake Superior, is the most inland point on the Saint Lawrence Seaway and the most inland port in the world.
Among the scenic places on the lake are Apostle Islands National Lakeshore, Brockway Mountain Drive on the Keweenaw Peninsula, Isle Royale National Park, Porcupine Mountains Wilderness State Park, Pukaskwa National Park, Lake Superior Provincial Park, Grand Island National Recreation Area, Sleeping Giant and Pictured Rocks National Lakeshore. The Great Lakes Circle Tour is a designated scenic road system connecting all of the Great Lakes and the St. Lawrence River.
Climate
Lake Superior's size reduces the severity of the seasons of its humid continental climate. The water surface's slow reaction to temperature changes, seasonally ranging between around 1970, helps to moderate surrounding air temperatures in the summer and winter, and creates lake-effect snow in colder months. The hills and mountains that border the lake hold moisture and fog, particularly in the fall.Geology
The rocks of Lake Superior's northern shore date back to the early history of the earth. During the Precambrian magma forcing its way to the surface created the intrusive granites of the Canadian Shield. These ancient granites can be seen on the North Shore today. It was during the Penokean orogeny, part of the process that created the Great Lakes tectonic zone, that many valuable metals were deposited. The region surrounding the lake has proved to be rich in minerals, with copper, iron, silver, gold and nickel the most frequently mined. Notable production includes gold from the Hemlo mine near Marathon, copper from the Keweenaw Peninsula and the Mamainse Point Formation, iron from the Gogebic Range, silver at Silver Islet, and uranium at Theano Point.The mountains steadily eroded, depositing layers of sediments that compacted and became limestone, dolomite, taconite and the shale at Kakabeka Falls. The continental crust was later riven, creating one of the deepest rifts in the world. The lake lies in this long-extinct Mesoproterozoic rift valley, the Midcontinent Rift. Magma was injected between layers of sedimentary rock, forming diabase sills. This hard diabase protects the layers of sedimentary rock below, forming the flat-topped mesas in the Thunder Bay area. Amethyst formed in some of the cavities created by the Midcontinent Rift, and there are several amethyst mines in the Thunder Bay area.
Lava erupted from the rift and formed the black basalt rock of Michipicoten Island, Black Bay Peninsula, St. Ignace Island, and Isle Royale.
In the most recent geological history, during the Wisconsin glaciation 10,000 years ago, ice covered the region at a thickness of. The land contours familiar today were carved by the advance and retreat of the ice sheet. The retreat left gravel, sand, clay and boulder deposits. Glacial meltwaters gathered in the Superior basin creating Lake Minong, a precursor to Lake Superior. Without the immense weight of the ice, the land rebounded, and a drainage outlet formed at Sault Ste. Marie, becoming today's St. Mary's River.