Week Three - Glaciers

Devil's Lake: Trapped by the End Moraine

Travis Suggitt

While working on a portion of the Ice Age Trail in southern Wisconsin, our crew spent the evenings swimming in nearby Devil's Lake. I was fortunate to make friends with Dave, an employee of the Ice Age Trail Alliance who is extremely knowledgeable on the area's formation. While sitting on the beach of the lake, Dave pointed at various features and described their geological history. He explained that until around 10,000 years ago, this lake was part of a river with the lake's east and west quartzite bluffs forming its banks.

Looking south-east across Devil's Lake, the ancient river's original path can be visualized as it would have followed the bluffs (Skillet Creek Media, 2020b).

Looking towards the south, one can see how the bluffs are connected by a shorter hill. This, Dave explained, is the end moraine, where a continental glacier ended its forward trajectory. As the glacier paused before receding, it deposited sediment that plugged the valley, keeping the river from flowing. Having hiked onto the moraine, I recall that the red to brown clay and soil distinct from the sandy pink colored metamorphic quartz boulders and rocks which form the bluffs, though some quartz erratics are found in the moraine. Dave claimed that igneous erratics can also be found less frequently in the moraine, likely carried a very long distance by the glacier.

The end moraine, which dammed Devil's Lake, is seen here as the shorter hill between the two bluffs (Skillet Creek Media, 2020a).

 

 

Pointing north, Dave explained that a less noticeable hill exists from the same process. The glacier wasn't able to cut through or go over the eastern quartzite bluff in its final advances, so the end moraine wraps around it leaving sedimentary dams on the north and south ends of Devil's Lake.

Photo References:

Skillet Creek Media. (2020a). Did glaciers make Devil's Lake? https://www.devilslakewisconsin.com/learning-center/did-glaciers-make-devils-lake/

Skillet Creek Media. (2020b). Tumbled Rocks Trail. https://www.devilslakewisconsin.com/activities/hiking/devils-lake-trail-details-descriptions/tumbled-rocks-trail/