- Minnesota Geology -
Lake Harriet - A Buried River Valley
The continental glaciers spreading over Minnesota during the Great Ice Ages brought vast quantities of rock material from the North to be dumped indiscriminately during the recession of the ice. Old river valleys were filled and belts of hills were formed as conditions changed. The Lake Harriet landscape has such an origin.
Leaving the present channel of the Mississippi River at the Plymouth Avenue Bridge, a pre-glacial valley runs almost directly south beneath Lake of the Isles, Lake Calhoun, and Lake Harriet to the Minnesota River at Bloomington. This valley was mostly filled but not completely obliterated by glacial deposits. The unfilled portions of the valley are now basins, which are filled by lakes perched high on glacial debris. Located last in a chain of five lakes located in Uptown Minneapolis, Lake Harriet lies directly over this ancient valley, formed as an ice block depression during the most recent glaciation. Its surface is in a setting of hills piled up while the ice front paused here in its final retreat about 10,000 years ago.
Lake Harriet has a surface area of 335 acres and is the second largest lake in Minneapolis. Its average depth of twenty-nine feet (eighty-two feet maximum). Now located in an urban residential area, the lake is fed largely by storm drainage, runoff, direct precipitation, and groundwater seepage. Throughout its history, Lake Harriet has undergone many changes, driven by both natural and human influences.
TO LOG THIS CACHE:
1) The former valley’s rocky floor is how many feet below you?
2) Record the shoreline surface water temperature.
E-mail me the answers HERE.
- Display- Geological Society of Minnesota and the Board of Park Commissioners 1955.
- Minneapolis Park and Recreation Board