Leech Lake is the third largest inland lake in Minnesota with over 102,000 acres of water surface and approximately 200 miles of shoreline. Only Red Lake and Mille Lacs Lake are larger. At one time, Leech Lake was covered by glaciers as much as two miles thick! Over the past two million years, this area was repeatedly crossed by glaciers coming from the north, northwest, and northeast.
The glaciers formed most of Minnesota’s lakes as ice block lakes whereby a chunk of ice broke off of an advancing glacier, became buried in the debris, and when the ice melted underneath the debris, the resulting holes of water became lakes.
But Leech Lake and only one other Minnesota lake, Mille Lacs, was formed differently. They are considered to be Moraine Lakes. The deposit of till (rock, sand and soil debris) left behind by a retreating glacier is called a moraine. A terminal moraine is the result of the debris left at the glacier’s endpoint. In the case of Leech Lake and Mille Lacs Lake, water backed up behind the terminal moraines of the advancing glaciers so that these moraines acted as natural dams preventing the glacial melt water from escaping.
To get credit for this earthcache, email the answers to the following questions:
- What is the elevation at this point?
- Describe the landform on the east lake shore. This is a terminal moraine. Estimate its height.
- Notice the island to the northwest. How do you think this was created?
- How many islands can you see from here?
- How did a terminal moraine form Leech Lake?