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57-485: Lake Agassiz ( / ˈ æ ɡ ə s i / AG -ə-see ) was a large proglacial lake that existed in central North America during the late Pleistocene , fed by meltwater from the retreating Laurentide Ice Sheet at the end of the last glacial period . At its peak, the lake's area was larger than all of the modern Great Lakes combined. It eventually drained into what is now Hudson Bay , leaving behind Lake Winnipeg , Lake Winnipegosis , Lake Manitoba , and Lake of

114-475: A glacial overspill channel created when the water of a proglacial lake rose high enough to breach the lowest point in the containing watershed. Traverse Gap The Traverse Gap was cut at the end of the last ice age . The Laurentide Ice Sheet decayed and receded as the Wisconsonian glaciation drew to a close, and Glacial Lake Agassiz formed from its meltwaters. The glacier blocked outlets to

171-498: A hazard for zones below. Many natural dams (usually moraines ) containing the lake water have been reinforced with safety dams. Some 34 such dams have been built in the Cordillera Blanca to contain proglacial lakes. Several proglacial lakes have also formed in recent decades at the end of glaciers on the eastern side of New Zealand's Southern Alps . The most accessible, Lake Tasman , hosts boat trips for tourists. On

228-646: A pipe at the divide." Its significance was also appreciated by early explorers, including Major Stephen Harriman Long , who led an expedition up the Minnesota River (then called St. Peter River) across the gap and down the Red River: ... we continued our journey in what appeared to have been an old water-course, and, within three miles of the Big Stone Lake, found ourselves on the bank of Lake Travers ... The space between Lakes Travers and Big Stone,

285-593: A short period of time. During this phase, the Clearwater and Athabasca River system outlet opened. Isostatic rebound opened the southern outlet for a time, creating the Norcross (325 metres (1,066 ft)), Tintah (310 metres (1,020 ft)), and Upper Campbell (299 metres (981 ft)) beaches. The south outlet was permanently closed at the end of Emerson Phase. The opening of the Kaministiquia outlet to

342-404: A smaller scale, a mountain glacier may excavate a depression forming a cirque , which may contain a mountain lake, called a tarn , upon the melting of the glacial ice. The movement of a glacier may flow down a valley to a confluence where the other branch carries an unfrozen river. The glacier blocks the river, which backs up into a proglacial lake, which eventually overflows or undermines

399-620: Is but very-little elevated above the level of both these lakes; and the water has been known, in times of flood, to rise and cover the intermediate ground, so as to unite the two lakes. In fact, both these bodies of water are in the same valley; and it is within the recollection of some persons, now in the country, that a boat once floated from Lake Travers into the St. Peter. Thus, therefore, this spot offers us one of those interesting phenomena, which we have already alluded to, but which are no where perhaps so apparent as they are in this place. Here we behold

456-519: Is crossed by Minnesota State Highway 28 , which becomes South Dakota Highway 10 at the south end of Lake Traverse. The uppermost part of the bed of Glacial River Warren, including Big Stone and Traverse lakes, has been designated as a National Natural Landmark under the Historic Sites Act under the name of Ancient River Warren Channel . It received this designation in April 1966 from

513-1009: Is the source of the Bois des Sioux River , a source stream of the Red River of the North , which drains via Lake Winnipeg and the Nelson River to Hudson Bay in the Arctic Ocean. To the south, Big Stone Lake is the source of River Warren's remnant, the Minnesota River , tributary to the Mississippi , which drains to the Gulf of Mexico and the Atlantic. Big Stone Lake is now fed by the Little Minnesota River ,

570-526: The Biblical flood narrative . The lowest point between the drainage of Hudson Bay and the Gulf of Mexico is in the Traverse Gap between the U.S. states of Minnesota and South Dakota . It lies between Lake Traverse and Big Stone Lake . This continental divide is about 300 metres (980 ft) above sea level. When Lake Agassiz existed, the gap was the outlet to River Warren . The outflow from

627-608: The Cordilleran Ice Sheet crept southward into the Idaho Panhandle , forming a large ice dam that blocked the mouth of the Clark Fork River , creating a massive lake 2,000 feet (600 m) deep and containing more than 500 cubic miles (2,000 km ) of water. Finally this Glacial Lake Missoula burst through the ice dam and exploded downstream, flowing at a rate 10 times the combined flow of all

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684-882: The Manitoba and North Dakota border, forming a crescent around the west side of the Turtle Mountains . Lake Souris had three successive outlets: the Sheyenne River , the Pembina River, and finally the Assiniboine River. Initially, Lake Souris' southern bay drained into the Sheyenne River, a tributary of the Red River, which in turn flowed into Lake Agassiz. However, after the ice sheet had retreated enough to uncover Turtle Mountain,

741-490: The North Saskatchewan River between Saskatoon and Prince Albert , Saskatchewan. A few miles east of Lake Saskatchewan's outlet, near the modern junction of the north and south branches, it entered Lake Agassiz. This Saskatchewan embayment extended for 400 miles (640 km) along the modern Saskatchewan River route. Raised beaches , many kilometres from any current water, mark the former boundaries of

798-758: The Perito Moreno Glacier , located in Patagonia . Roughly every four years the glacier forms an ice dam against the rocky coast, causing the waters of the Lago Argentino to rise. When the water pressure is too high, then the giant bridge collapses in what has become a major tourist attraction. This sequence occurred last on 4 March 2012, the previous having taken place four years before, in July 2008. About 13,000 years ago in North America,

855-512: The Red River Valley , now drained by the Red River of the North , were formed from lacustrine deposits of silt from Lake Agassiz. [REDACTED] Wetlands portal Proglacial lake In geology, a proglacial lake is a lake formed either by the damming action of a moraine during the retreat of a melting glacier , a glacial ice dam, or by meltwater trapped against an ice sheet due to isostatic depression of

912-653: The Saskatchewan River flows; Lake Dauphin , south of Lake Winnipegosis and tributary to it; and Lake St. Martin , on the Fairford or Little Saskatchewan River , the outlet of lakes Manitoba and Winnipegosis. In northern Minnesota, there are Roseau , Thief , Mud , and Maple lakes , besides three large lakes of that state, Rainy Lake , the Lake of the Woods , and Red Lake . Glacial Lake Souris formed along

969-711: The Traverse Gap at Brown's Valley is at 980 feet (300 m). This was the south outlet of Lake Agassiz. The Herman Beach displays numerous deltas from the major rivers that entered Lake Agassiz. In Minnesota and North Dakota, these include the Buffalo River Delta, Sand Hill River Delta, Sheyenne River Delta, Elk Valley Delta, and the Pembina River Delta. In Manitoba, there is the Assiniboine River Delta. Fourteen shorelines of Lake Agassiz have been identified, which lie below

1026-723: The Arctic Ocean about 13,000 years ago. The ice returned to the south for a time, but as it again retreated north of the present Canada–United States border around 10,000 years ago, Lake Agassiz refilled. The last major shift in drainage occurred around 8,200 years ago. The melting of remaining Hudson Bay ice caused Lake Agassiz to drain nearly completely. This final drainage of Lake Agassiz has been associated with an estimated 0.8 to 2.8 m (2.6 to 9.2 ft) rise in global sea levels . Lake Agassiz's major drainage reorganization events were of such magnitudes that they significantly impacted climate, sea level, and possibly early human civilization . The lake's enormous freshwater release into

1083-584: The Arctic Ocean has been postulated to have disrupted oceanic circulation and caused temporary cooling. The draining of 13,000 years ago may be the cause of the Younger Dryas stadial . Although disputed, the draining at 9,900–10,000 years ago may be the cause of the 8,200 yr climate event . A study by Turney and Brown links the 8,500-years-ago drainage to the expansion of agriculture from east to west across Europe; they suggest that this may also account for various flood myths of ancient cultures, including

1140-468: The Assiniboine River, Lake Souris drained via that river into Lake Agassiz. ( Pelican Lake in Langs Valley of Manitoba occupies what was once the northern shore of Lake Souris.) The lower part of the Saskatchewan River basin near the river's mouth at Cedar Lake was clear of the ice-sheet before Lake Agassiz began to drain to northeast. Lake Saskatchewan existed on about 135 miles (217 km) of

1197-427: The Atlantic basin. The ancient channel at Browns Valley is a mile (1.6 km) wide and some 130 feet (40 m) deeper than the surrounding terrain through which it was carved. The distance from Lake Traverse to Big Stone Lake is about five miles (8.0 km). The ancient channel through the moraine includes not only the land between those modern lakes, but the lakes themselves. The continental divide crosses

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1254-541: The Emerson Phase, lake levels and drainage patterns continually fluctuated. The lake switched from a southward outlet to a northwestern outlet, and may have been static without a significant outlet during this phase. Isostatic rebound changed the elevation of the land, and this, combined with changes in the volume of meltwater from the ice margin and the closure of the Kaministikwia outlet in the east increased

1311-531: The Herman lake beaches until isostatic rebound and glacial advances closed the Kaministikwia route. This stabilized the lake at the Norcross lake stage (325 metres (1,066 ft)). The average depth of Lake Agassiz during the late Moorhead Phase was 258 metres (846 ft). Drainage from Lake Agassiz continued to flow southward out of the ancient Minnesota and Mississippi River systems into the Gulf of Mexico. During

1368-563: The Lake Nipigon and Superior basins. A dozen beaches were created during short periods of stability. Towards the end of the Nipigon Phase, Lake Agassiz reached its largest geographical size as it joined with Lake Ojibway in the east. The Ojibway Phase is named for the glacial lake along the ice front in northern Ontario . Lake Ojibway merged with Lake Agassiz at this time. Isostatic rebound of glaciated lands that were south of

1425-574: The Lake Nipigon outlet and the other low level outlets, creating intermittent catastrophic outbursts of water into the Lake Minong basin. These large inflows of water raised Lake Minong lake levels and flowed into Lake Algonquin in the Lake Michigan and Huron basins. These outbursts refilled the Lake Michigan and Huron basins, which are extreme low water levels of Lake Chippewa (Lake Michigan basin) and Lake Stanley (Lake Huron basin). This

1482-750: The McCauleyville beaches. These formed when the River Warren could no longer receive the outflow of the lake. This occurred when a lower outlet was found and the lake shrank with the release of the lake's waters. The three highest shorelines are named the Blanchard beaches, and the next five in descending order are the Hillsboro, the two Emerado, and the two Ojata beaches, from towns on or near their course in North Dakota. The fertile soils of

1539-729: The Ojibway Phase of Lake Agassiz and may indicate large amounts of drainage from the Ottawa River valley and the Tyrrell Sea (ancestral Hudson Bay). The Laurentide Ice Sheet continued to recede. Continued warming shrank the ice front towards present day Hudson Bay. Here, the Lake Agassiz northward outlet drained into the Tyrrell Sea. This breach dropped the water level below the eastern Kinojevis outlet. The drainage

1596-656: The Traverse Gap, now occupied by much smaller lakes and watercourses and a flat valley floor containing marshes, agricultural land, and the small community of Browns Valley, Minnesota . Despite the low elevation and flat topography of its floor, the Traverse Gap marks the southernmost point of the Northern Divide between the watersheds of the Arctic and the Atlantic Oceans. On the north, Lake Traverse

1653-401: The Woods . First postulated in 1823 by William H. Keating , it was named by Warren Upham in 1879 after Louis Agassiz , the then recently deceased (1873) founder of glaciology , when Upham recognized that the lake was formed by glacial action. During the last glacial maximum , northern North America was covered by an ice sheet , which alternately advanced and retreated with variations in

1710-653: The climate. This continental ice sheet formed during the period now known as the Wisconsin glaciation , and covered much of central North America between 30,000 and 10,000 years ago. As the ice sheet disintegrated, its meltwaters created an immense proglacial lake . Around 13,000 years ago, this lake came to cover much of what are now southeastern Manitoba , northwestern Ontario , northern Minnesota , eastern North Dakota , and Saskatchewan . At its greatest extent, it may have covered as much as 440,000 km (170,000 sq mi), larger than any currently existing lake in

1767-402: The continental divide into the other basin in times of high water. The maximum elevation on the floor of the valley is 987 feet (301 m) above sea level. The Browns Valley Dike at the south end of Lake Traverse is at the same elevation; this structure was built to reduce the likelihood of flooding south across the continental divide. At 983.9 feet (299.9 m), that divide is lower than

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1824-433: The crust around the ice. At the end of the last ice age about 10,000 years ago, large proglacial lakes were a widespread feature in the northern hemisphere. The receding glaciers of the tropical Andes have formed a number of proglacial lakes, especially in the Cordillera Blanca of Peru, where 70% of all tropical glaciers are. Several such lakes have formed rapidly during the 20th century. These lakes may burst, creating

1881-553: The earliest of the Red River Trails . The area was surveyed and sold to the public in the latter part of the nineteenth century. The rural part of the valley floor contains pastures, cropland, and marshes along the Little Minnesota River. The vale was named "Browns Valley" after one of its pioneer residents, which in turn gave its name to the incorporated community near its northern end. The valley floor

1938-677: The east initiated the onset of the Nipigon Phase. The lower lake level ended the southern outlet through the ancestral Minnesota and Mississippi River systems. The ice sheets advanced and blocked the northwestern outlet through the Clearwater and Athabasca systems. There were several other low level outlets into the Lake Minong basin, including the Kaministiquia and the Lake Nipigon outlet. These allowed large amounts of water to flow from Lake Agassiz into Lake Minong. A series of ice advances and retreats between 10,500 and 9,500 YBP blocked

1995-537: The former lakebed of Lake Agassiz to Lake Winnipeg . During the Lockhart Phase, water accumulated in the Red River valley of North Dakota and Minnesota . As the water reached to the top of the divide to the south, the water drained into the ancestral Minnesota and Mississippi River systems. This occurred while the Laurentian Ice Sheet was at or south of the current Canada–US border. As

2052-586: The gap transversely at its northern end. The Minnesota-South Dakota border longitudinally bisects the old channel. Roberts County is on the South Dakota side. To the east is Traverse County, Minnesota and the community of Browns Valley near the continental divide. The southeast part of the gap is in Big Stone County, Minnesota . The area has seen human presence for thousands of years. A Paleo-Indian skeleton now known as " Browns Valley Man "

2109-460: The headwaters of which are in South Dakota. The Little Minnesota enters the gap from the west and meanders south through the old channel to Big Stone Lake. The Little Minnesota, part of the Mississippi watershed, is less than one mile (1.6 km) from Lake Traverse in the drainage basin of Hudson Bay. The floor of Browns Valley is flat, which allows the waters of one basin to flood across

2166-531: The ice dam, suddenly releasing the impounded water in a glacial lake outburst flood also known by its Icelandic name a jökulhlaup . Some of the largest glacial floods in North American history were from Lake Agassiz . In modern times, the Hubbard Glacier regularly blocks the mouth of Russell Fjord at 60° north on the coast of Alaska. A similar event takes place after irregular periods in

2223-769: The ice sheet created a long linear lake from the Saskatchewan – Manitoba border to Quebec . This long lake drained through the eastern outlet at Kinojevis River  [ fr ] , into the Ottawa River valley. Lake Agassiz-Ojibway drainage raised sea levels. The results can be seen in Nova Scotia , New Brunswick , and eastern Maine . Marine records from the North Atlantic have identified two separate episodes, linked to northern hemisphere cooling in 8,490 YBP and 8,340–8,180 YBP. These may be linked with

2280-462: The ice sheet melted northward, an early Lake Agassiz covered southern Manitoba , the Minnesota and Ontario boundary country, and along the Red River south of Fargo, North Dakota . The Lockhart Phase is associated with the Herman lake stage (335 metres (1,099 ft)), the highest shoreline of Lake Agassiz. The Big Stone Moraine formed the southern boundary of the lake. During the Lockhart Phase

2337-578: The lake is estimated to have been 231 metres (758 ft) deep, with greater depths near the glacier. As the ice sheet melted northward, Lake Agassiz found a lower outlet through the Kaministikwia route along the modern Minnesota–Ontario border. This moved water to Lake Duluth , a proglacial lake in the Lake Superior basin. From there the water drained south via an ancestral St. Croix and Mississippi River systems. The lake drained below

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2394-717: The lake. While the Red River gradually descends from south to north, these old strandlines ascend as one goes north, due to isostatic rebound since glaciation. The highest shore of Lake Agassiz is called the Herman Beach . It is named for Herman, Minnesota , in Grant County . The Herman Beach is the highest shoreline and can be traced from the historic outlet at Lake Traverse on the border of Minnesota and South Dakota. The beach fluctuates between 973 and 976 feet (296.5 and 297.5 m) above sea level. The altitude of Lake Traverse at 971 feet (296 m) above sea level at

2451-531: The level of the dike, and flooding at Lake Traverse has the potential to drain over the Browns Valley Dike into the Minnesota River watershed. At the south end of the gap, the Big Stone Lake reservoir pool is maintained at 967 feet (295 m), but flooded to over 975 feet (297 m) in 1997. The Little Minnesota River upstream and at a higher elevation near the divide has flooded to a level where it drained across that divide into Lake Traverse. While

2508-510: The melting glaciers filled Lake Agassiz and then drained through the gap to the Gulf of Mexico. This mass of moving water eroded a valley 2–5 kilometres (1.2–3.1 mi) wide and from 100 to 125 feet (30 to 38 m) deep. Today, this valley contains the Minnesota River , joined by the Upper Mississippi River at Fort Snelling, Minnesota . North of the gap, the Red River of the North flows from Lake Traverse north through

2565-402: The natural state of the area has been altered by the dike and control structures on the two lakes, interbasin flooding did occur prior to construction of those improvements. The Traverse Gap therefore allows waters which would naturally flow to the Gulf of Mexico to flow to the Arctic instead, and in the past has allowed water from Lake Traverse to flow in the other direction to Big Stone Lake in

2622-480: The north, and the outlet to the south was dammed by the Big Stone Moraine, a terminal moraine left by the ice sheet's retreat. Lake Agassiz filled until it overtopped the moraine about 11,700 years ago. The resulting enormous outflow of the lake carved a deep spillway through the moraine, through which cascaded Glacial River Warren . This great river not only created the gap, it also cut the valleys of

2679-601: The northern bay of Lake Souris found an outlet at the "elbow" of the modern Souris River ; the elbow is about 18 miles (29 km) southwest of the present mouth of the Souris River. From this elbow, the lake's waters flowed southeast and entered the Pembina River , now a tributary of the Red River , and the Pembina, in turn, entered Lake Agassiz at its Assiniboine embayment. When the ice sheet retreated north of

2736-413: The present-day Minnesota and Upper Mississippi Rivers . River Warren drained Agassiz twice more over the next 2,300 years, separated by intervals when the ice sheet receded sufficiently to uncover other outlets for Lake Agassiz. About 9,400 years ago, Agassiz found a permanent outlet to the north. With its former source now draining elsewhere, River Warren ceased to flow, and the spillway gorge became

2793-563: The rapid and catastrophic release of dammed water resulting in the formation of gorges and other structures downstream from the former lake. Good examples of these structures can be found in the Channeled Scablands of eastern Washington, an area heavily eroded by the Missoula Floods . The following table is a partial list of rivers that had glacial ice dams. The retreating glaciers of the last ice age, both depressed

2850-441: The rivers of the world. Because such ice dams can re-form, these Missoula Floods happened at least 59 times, carving Dry Falls below Grand Coulee . In some cases, such lakes gradually evaporated during the warming period after the Quaternary ice age. In other cases, such as Glacial Lake Missoula and Glacial Lake Wisconsin in the United States, the sudden rupturing of the supporting dam caused glacial lake outburst floods ,

2907-421: The size of the northern end of the lake. One hypothesis postulates that the lake was a ' terminal lake ' with water inflows and evapotranspiration being equal. Dating of the glacial moraines shows that the Clearwater and Athabasca River system and Lake Nipigon and Minong basin were still ice-covered. A period of precipitation and meltwater input balance with the rate of evapotranspiration may have existed for

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2964-547: The terrain with their mass and provided a source of meltwater that was confined against the ice mass. Lake Algonquin is an example of a proglacial lake that existed in east-central North America at the time of the last ice age . Parts of the former lake are now Lake Huron , Georgian Bay , Lake Superior , Lake Michigan and inland portions of northern Michigan. Examples in Great Britain include Lake Lapworth , Lake Harrison and Lake Pickering . Ironbridge Gorge in Shropshire and Hubbard's Hills in Lincolnshire are examples of

3021-460: The waters of two mighty streams, one of which empties itself into Hudson's Bay at the 57th parallel of north latitude, and the other into the Gulf of Mexico, in latitude 29°, rising in the same valley within three miles of each other, and even in some cases offering a direct natural navigation from one into the other. The native trails were later used by fur traders who had posts at Lake Traverse and Big Stone Lake, and then by Red River ox carts on

3078-415: The world (including the Caspian Sea ) and approximately the area of the Black Sea . At times the lake drained south through the Traverse Gap into Glacial River Warren (parent to the Minnesota River , a tributary of the Mississippi River ), east through Lake Kelvin (modern Lake Nipigon ) to what is now Lake Superior , and northwest through the Clearwater Spillway to the Mackenzie River System and

3135-436: Was due to isostatic rebound of the northern shorelines combined with the opening of the North Bay outlet of the Lake Huron basin. These repetitive outbursts from Lake Agassiz flooded the Lake Minong basin, then flowed over into the Lake Stanley basin, and then flowed through the North Bay drainage route into the Champlain Sea (present day St. Lawrence lowland). The shifting ice sheet created fluctuating drainage channels into

3192-489: Was followed by the disintegration of the adjacent ice front at about 8,480 YBP. This brought on the end of Lake Agassiz. The ice sheet continued its northward retreat to Baffin Island , leaving the North American mainland around 5,000 YBP. Numerous lakes have formed in this glacial lake basin. The best known are the Great Lakes of Manitoba ; Lake Winnipeg , Lake Manitoba , and Lake Winnipegosis . A cluster of smaller lakes surround these, including: Cedar Lake , through which

3249-430: Was unearthed in 1933 under circumstances which suggested death or interment after deposition of the gravel but before creation of significant topsoil. Found with tools of the Clovis and Folsom types, the human remains have been dated approximately 9,000 years b.p. The Traverse Gap was used by Native Americans , who "from time immemorial ... had placed two weather-beaten buffalo skulls where travelers paused to smoke

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