Glacial River Warren

River Warren (English and Glacial River Warren ) was a prehistoric lakebed, the dewatered the Lake Agassiz in the middle of North America in the period before 11,700 and 9,400 years. The enormous amount of water exiting the lake, created a mighty valley, which is now traversed by the much smaller Minnesota River and the headwaters of the Mississippi River.

The Lake Agassiz was formed by the melt waters of the Laurentide Ice Sheet, as of the last ice age, the ice sheet prevented the flow of water to the north during the Wisconsin glaciation. The Agassiz was a large accumulation of water, about 200 feet deep and at various times it covered an area of ​​300,000 square kilometers. The water level rose until about 11,700 years, until he finally overcame the Big Stone Moraine, which had been created by the retreating glaciation. Browns Valley, Minnesota, the effluent water, the bed took some catastrophic cut a gorge through the moraine, which is about 1.6 km wide and about 40 meters deep and under the name Traverse Gap is known today.

Here the lakebed River Warren began. From its creation until complete drying up of the southern outflow of Agassiz flowed through the Traverse Gap, the Laurentide ice sheet melt water from the valley of the Mississippi. However, this did not happen continuously, but by the advance and retreat of the ice sheet and the ice thickness during different climatic phases emerged isostatic changes in land levels, which in turn other outflows of the lake allowed or blocked from the sea.

During its existence, the primordial stream cut into the landscape and eroded an up to 8 km wide and 80 meters deep valley. This valley begins at the Traverse Gap at Browns Valley, Minnesota, leads southwest to Mankato, then turns to the northeast of the Twin Cities, where the relatively smaller Mississippi River flowed into the lakebed. River Warren undercut the smaller river at the site of Fort Snelling and created waterfalls that have since migrated through headward erosion of the Mississippi upwards and now form the Falls Minnehaha Falls and Saint Anthony Falls in Minneapolis. From Fort Snelling the valley continues northeast to today's Saint Paul and then turns to the southeast in the direction of Prescott, where the St. Croix River flows, which once was an outflow of another glacial lake itself, the Duluthsee in the western part of present-day Lake Superior. From its confluence with the St. Croix valley leads to the southeast, where today are the limits between Minnesota and Wisconsin. River Warren caused the formation of cliff- like shores sections in the valleys of the Mississippi and Minnesota and contributed to the formation of the Lake Pepin at.

Approximately 9400 years ago, the ice sheet retreated so far that the Agassiz could permanently take another run-off and fell below the level of the Traverse Gap. Warren River dried up. The catchment area of ​​Lake Agassiz feeds today the Red River of the North, which flows north and eventually empties into Hudson Bay. The upper valley of the River Warren in the Traverse Gap now flow through the Little Minnesota River, which flows into the Big Stone Lake and the Minnesota River, which follows the former glacial valley up to its confluence with the Mississippi. Both streams occupy only a portion of the former bed of the River Warren.

Naming

The hydrology of the vast valleys was first declared in 1868 by General Gouverneur Kemble Warren. He examined the region in search of a possible route for the railroad trankontinentale. After his death, the prehistoric river to his honor River Warren was called.