Tuesday, April 21, 2015

Day hiking trail heads along edge of ancient Glacial Lake Duluth

Brule River Outlet Trail

Ice Age lake
once covered

Day hikers can wander among the remains of an ancient glacial lake that significantly shaped the Upper Midwest.

The Brule River Outlet Trail runs about 3-miles round trip in Wisconsin’s Brule River State Forest. An unnamed trail, it has been christened here for the major geological event that occurred in the region about 9000-8500 BC.

To reach the trailhead, from Brule, head west on U.S. Hwy 2. Turn left/west onto Afterhours Road. In about 2000 feet, as the road curves southwest, watch for unmarked trailheads on the left/southeast. Should the road curve straight west, you’ve gone too far. Park off the side of the road and take the trail southeast into the woodlands.

Lake bottom
Upon hitting the trail, you’re walking at the edge of ancient Glacial Lake Duluth near its outlet to the Bois-Brule River. About 11,000 years ago during the last ice age as the Superior Lobe glacier advanced westward, it blocked the outlets of rivers flowing eastward. The water collected between the ice wall and the basin, resulting in several lakes.

When the lobe retreated, those lakes coalesced to form a larger one called Glacial Lake Duluth. Located in modern Lake Superior’s southwestern corner, it stretched as far east as Marquette, Mich., and as far north as Grand Portage, Minn. It also covered what is now dry land in Wisconsin, Minnesota and Michigan, as the waterbody was 500 feet higher than modern Lake Superior.

After walking about 400 feet, the trail comes to its first major intersection; go right/west. The trail then zig zags for the next 1400 feet until cutting a straight line that heads southeast toward the Brule River.

In its day, Glacial Lake Duluth drained through the Bois-Brule River south to the St. Croix River on its way to the Mississippi River. The hills to the trail’s west – which reach 1100 feet elevation – marked the lake’s shoreline. The trail itself would have been about a hundred feet below the lake’s surface.

A major flashflood when an ice dam broke on Glacial Lake Duluth carved out the St. Croix River Valley to the southwest; many of the impressive geological features of Wisconsin and Minnesota Interstate Parks occurred during that flood. The lake also left a flat plain of red clay and sediment that sits on the modern Lake Superior shoreline of Wisconsin and Minnesota.

New river course
After about 500 years, the glacial lake disappeared. As the Superior Lobe retreated, it left a gouge in the landscape that became Lake Superior and freed the local rivers’ outlet to the other Great Lakes and the St. Lawrence River.

Since then, with the heavy glaciers’ disappearance, the land has rebounded upward. The Bois Brule now flows northward into Lake Superior with the space between the Bois Brule and the St. Croix becoming a wetlands that sits at a higher elevation than either river.

Back on the trail, upon reaching the ridge overlooking the Brule, the route curves southwest and descends the bluffs to the river valley. In this area, the basin narrowed enough that the only place for the glacial lake to flow was an outlet into the Bois-Brule about where modern Hoodoo Lake is.

The trail next reaches a jeep road just north of Little Joe Rapids. This marks a good spot to turn back.

Learn about trail guidebooks available in the Hittin’ the Trail series.