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31-583: Lake Agassiz was formed from the meltwaters of the Laurentide Ice Sheet during the Wisconsin glaciation of the last ice age . Agassiz was an enormous body of water, up to 600–700 ft (180–210 m) deep, and at various times covering areas totaling over 110,000 sq mi (280,000 km). Blocked by an ice sheet to the north, the lake water rose until about 13,500 BP calibrated (11,700 C uncalibrated) years ago when it overtopped

62-635: A dome over west-central Keewatin (Kivalliq). Two of the lobes abut the adjacent Labrador and Baffin ice sheets. The primary lobes flow (1) towards Manitoba and Saskatchewan ; (2) toward Hudson Bay ; (3) towards the Gulf of Boothia , and (4) towards the Beaufort Sea . The Labrador ice sheet flowed across all of Maine and into the Gulf of St. Lawrence , completely covering the Maritime Provinces . The Appalachian Ice Complex, flowed from

93-624: A large portion of the Northern United States , multiple times during the Quaternary glaciation epochs, from 2.58 million years ago to the present. The last advance covered most of northern North America between c. 95,000 and c. 20,000 years before the present day and, among other geomorphological effects, gouged out the five Great Lakes and the hosts of smaller lakes of the Canadian Shield . These lakes extend from

124-640: A reduction in precipitation , is likely to be the cause. If a single river appears to be a misfit stream, it may be as a result of human activity through groundwater extraction or dam construction upstream. Natural causes include stream capture or other changes in drainage patterns. For instance, New Zealand's largest river (the Waikato ) used to flow through the Hauraki Plains to the North Island 's east coast, but changed its course to exit on

155-562: Is believed that the Cordilleran ice melted rapidly, in less than 4000 years. The water created numerous Proglacial lakes along the margins such as Lake Missoula , often leading to catastrophic floods as with the Missoula Floods . Much of the topography of Eastern Washington and northern Montana and North Dakota was affected. The Keewatin ice sheet has had four or five primary lobes identified ice divides extending from

186-544: Is too large for either its valley or meanders, it is known as an overfit stream . If the misfit stream is too small for either its valley or meanders, it is known as an underfit stream . The term misfit stream is often incorrectly used as a synonym for an underfit stream. An underfit stream is a type of misfit stream whose discharge is too small to be correlated with either existing channel characteristics, i.e. meander radius, wavelength and channel width, or valley size An underfit stream can result when glaciation modifies

217-535: The Big Stone Moraine , a ridge of glacial drift left by the receding glacier, at the location of Browns Valley, Minnesota . The lake's outflow was catastrophic, and carved a gorge through the moraine 1 mi (1.6 km) wide and 130 ft (40 m) deep, which is now known as the Traverse Gap . The channel through the moraine, between Lake Traverse and Big Stone Lake , is now crossed by

248-768: The Gaspé Peninsula over New Brunswick , the Magdalen Shelf , and Nova Scotia . The Labrador flow extended across the mouth of the St. Lawrence River , reaching the Gaspé Peninsula and across Chaleur Bay . From the Escuminac center on the Magdalen Shelf , flowed onto the Acadian Peninsula of New Brunswick and southeastward, onto the Gaspe, burying the western end of Prince Edward Island and reached

279-803: The Last Glacial Maximum . The eastern edge abutted the Laurentide ice sheet. The sheet was anchored in the Coast Mountains of British Columbia and Alberta , south into the Cascade Range of Washington . That is one and a half times the water held in the Antarctic . Anchored in the mountain backbone of the west coast, the ice sheet dissipated north of the Alaska Range where the air was too dry to form glaciers. It

310-728: The Northeastern United States , and cities such as Boston and New York City and Great Lakes coastal cities and towns as far south as Chicago and St. Louis, Missouri , and then followed the present course of the Missouri River up to the northern slopes of the Cypress Hills , beyond which it merged with the Cordilleran Ice Sheet . The ice coverage extended approximately as far south as 38 degrees latitude mid-continent. This ice sheet

341-736: The Red River of the North which flows north, ultimately to Hudson Bay . River Warren's upper valley in the Traverse Gap is now occupied by the tiny Little Minnesota River , which flows into Big Stone Lake and the Minnesota River, which follows the greater river's ancient bed to its confluence with the Mississippi River. These misfit streams occupy only a small cross-section of River Warren's riverbed. The hydrology of

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372-705: The enormous weight of the melted ice . The Baffin ice sheet was circular and centered over the Foxe Basin . A major divide across the basin, created a westward flow across the Melville Peninsula , from an eastward flow over Baffin Island and Southampton Island . Across southern Baffin Island, two divides created four additional lobes. The Penny Ice Divide split the Cumberland Peninsula , where Pangnirtung created flow toward Home Bay on

403-575: The Atlantic Ocean. Its cycles of growth and melting were a decisive influence on global climate during its existence. This is because it served to divert the jet stream southward, which would otherwise flow from the relatively warm Pacific Ocean through Montana and Minnesota . That gave the Southwestern United States , otherwise a desert, abundant rainfall during ice ages, in extreme contrast to most other parts of

434-455: The Baffin ice flow, but an autonomous flow. Misfit stream A misfit stream is a river that is either too large or too small to have eroded the valley or cave passage in which it flows. This term is also used for a stream or river with meanders that obviously are not proportional in size to the meanders of the valley or meander scars cut into its valley walls. If the misfit stream

465-867: The Laurentide Ice Sheet. Central North America has evidence of the numerous lobes and sublobes. The Keewatin covered the western interior plains of North America from the Mackenzie River to the Missouri River and the upper reaches of the Mississippi River . The Labrador covered spread over eastern Canada and the northeastern part of the United States abutting the Keewatin lobe in the western Great Lakes and Mississippi valley . The Cordilleran ice sheet covered up to 2,500,000 square kilometres (970,000 sq mi) at

496-856: The Laurentide ice sheet reached from the Rocky Mountains eastward through the Great Lakes , into New England , covering nearly all of Canada east of the Rocky Mountains. Three major ice centers formed in North America: the Labrador , Keewatin , and Cordilleran . The Cordilleran covered the region from the Pacific Ocean to the eastern front of the Rocky Mountains and the Labrador and Keewatin fields are referred to as

527-437: The Minnesota River valley until they reached an older buried river valley about 2 mi (3.2 km) west of the confluence, where the falls were extinguished. From Saint Paul the great valley goes southeast to Prescott, Wisconsin , where it is joined by the St. Croix River , itself once the outlet of another proglacial lake , Glacial Lake Duluth which occupied the western part of Lake Superior . From its confluence with

558-667: The St. Croix the valley continues southeast along the Minnesota–Wisconsin border. River Warren's effects include the creation of bluffs along the valleys of the Minnesota and Mississippi Rivers, and contributed to the formation of Lake Pepin . By about 9400 BP, the ice sheet finally retreated sufficiently far to the north that Lake Agassiz permanently took another outlet and receded below the level of Traverse Gap. River Warren then ceased to run. The Lake Agassiz area watershed now feeds

589-739: The divide between the watersheds of the Gulf of Mexico and Hudson Bay . Its significance was recognized by designation as a National Natural Landmark under the Historic Sites Act . From Traverse Gap issued Glacial River Warren. From its inception until final abandonment of Agassiz' southern outlet, this stream drained the meltwater of that lake to the Mississippi valley. The drainage was not continuous, as Lake Agassiz periodically had other outlets. The Laurentide Ice Sheet retreated and advanced with climatic variations and these changes in ice cover contributed to isostatic adjustments in

620-487: The eastern Northwest Territories , through most of northern Canada, and the upper Midwestern United States ( Minnesota , Wisconsin , and Michigan ) to the Finger Lakes , through Lake Champlain and Lake George areas of New York , across the northern Appalachians into and through all of New England and Nova Scotia . At times, the ice sheet's southern margin included the present-day sites of coastal towns of

651-526: The formation of North Atlantic Deep Water , the very saline, cold, deep water that flows from the Greenland Sea . That interrupted the thermohaline circulation , creating the brief Younger Dryas cold epoch and a temporary re-advance of the ice sheet, which did not retreat from Nunavik until 6,500 years ago. After the end of the Younger Dryas, the Laurentide Ice Sheet retreated rapidly to

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682-565: The head of Bay of Fundy . From the Gaspereau center, on the divide crossing New Brunswick flowed into the Bay of Fundy and Chaleur Bay. In New York, the ice that covered Manhattan was about 2,000 feet high before it began to melt in about 16,000 BC. The ice in the area disappeared around 10,000 BC. The ground in the New York area has since risen by more than 150 ft because of the removal of

713-562: The landscape by creating glacial troughs . The rivers that occupy such valleys after the ice has retreated are not in proportion with the size of the valley . Given the scale of most glacial troughs almost all of them contain misfit streams. Misfit streams can also be caused by reductions in the discharge of the stream. Channel size responds rapidly to variations in discharge, but valley size responds over much longer timescales. Many causes of reduced discharges are possible. If misfit streams are widespread in an area, climate change , particularly

744-485: The level of the land over which the watercourses ran. These changes in turn uncovered or blocked the lake's other outlets to the sea. While active this turbulent stream cut and eroded a bed up to 5 mi (8.0 km) wide and 250 ft (76 m) deep, leaving a valley which starts at Traverse Gap near Browns Valley, Minnesota , goes southeast to Mankato , then turns northeast to the Twin Cities . River Warren

775-527: The north and Cumberland Sound on the south. The Amadjuak Ice Divide on the Hall Peninsula , where Iqaluit sits created a north flow into Cumberland Sound and a south flow into the Hudson Strait . A secondary Hall Ice Divide formed a link to a local ice cap on the Hall Peninsula . The current ice caps on Baffin Island are thought to be a remnant from this time period, but it was not a part of

806-611: The north, becoming limited to only the Canadian Shield until even it became deglaciated. The ultimate collapse of the Laurentide Ice Sheet is also suspected to have influenced European agriculture indirectly through the rise of global sea levels. Canada's oldest ice is a 20,000-year-old remnant of the Laurentide Ice Sheet called the Barnes Ice Cap , on central Baffin Island . During the Late Pleistocene ,

837-448: The oversized valley was first explained by General G. K. Warren in 1868. He made a detailed survey of the valley in his search for possible transcontinental railroad routes . In appreciation of this work, the glacial river that was the outlet of Lake Agassiz was named River Warren. Laurentide Ice Sheet The Laurentide ice sheet was a massive sheet of ice that covered millions of square miles, including most of Canada and

868-540: The surface geology of southern Canada and the northern United States, leaving behind glacially scoured valleys, moraines , eskers and glacial till . It also caused many changes to the shape, size, and drainage of the Great Lakes. As but one of many examples, near the end of the last ice age, Lake Iroquois extended well beyond the boundaries of present-day Lake Ontario , and drained down the Hudson River into

899-597: The world which became exceedingly dry, though the effect of ice sheets in Europe had an analogous effect on the rainfall in Afghanistan , parts of Iran , possibly western Pakistan in winter, as well as North Africa . Its melting also caused major disruptions to the global climate cycle, because the huge influx of low- salinity water into the Arctic Ocean via the Mackenzie River is believed to have disrupted

930-559: Was joined by the comparatively small Mississippi at Fort Snelling , from which the valley continues northeast to present-day Saint Paul , where the massive River Warren Falls once graced the landscape. Over 1700 years this waterfall retreated upstream and undercut the Mississippi at the site of Fort Snelling . The falls then split. The Mississippi falls migrated upstream to form Saint Anthony Falls and create Minnehaha Falls in Minneapolis . The River Warren falls receded west in

961-705: Was the primary feature of the Pleistocene epoch in North America, commonly referred to as the ice age . During the Pre-Illinoian Stage , the Laurentide Ice Sheet extended as far south as the Missouri and Ohio River valleys. It was up to 2 mi (3.2 km) thick in Nunavik , Quebec , Canada , but much thinner at its edges, where nunataks were common in hilly areas. It created much of

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