Glacial River Warren

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 km2).

[3] Blocked by an ice sheet to the north, the lake water rose until about 13,500 BP calibrated (11,700 14C uncalibrated) years ago when it overtopped 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,[4] 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.

From its inception until final abandonment of Agassiz' southern outlet, this stream drained the meltwater of that lake to the Mississippi valley.

[7] While active this turbulent stream cut and eroded a bed up to 5 mi (8.0 km) wide and 250 ft (76 m) deep,[8] leaving a valley which starts at Traverse Gap near Browns Valley, Minnesota, goes southeast to Mankato, then turns northeast to the Twin Cities.

[10] 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.

The valley of River Warren shows in this shaded relief image. At the upper left (northwest) is the bed of Lake Agassiz ; its outflow breached the U-shaped Big Stone Moraine at Traverse Gap and became the source of River Warren. At the extreme right, the northernmost oxbow loop is the Mississippi at downtown Saint Paul . Just to its west and almost invisible is the valley of the Mississippi above its confluence with River Warren at Fort Snelling .
This shaded relief image shows the area of Minneapolis-St. Paul . The wide channel of River Warren enters the image from the southwest. The Mississippi enters from the north near the left side and the St. Croix enters from the north at the right. The present rivers are grossly underfit for their valleys; the widening of the Mississippi to the southeast is the slackwater pool from Lock and Dam No. 2 .
The Minnesota River Valley and tributaries as seen from an airliner at Redwood Falls, Minnesota . The Minnesota River occupies only a small portion of the wide valley carved by the Glacial River Warren.