Lake Mille Lacs EarthCache
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LAKE MILLE LACS
| Second Largest Lake in Minnesota |
| How did it form? |
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Almost all the lakes in Minnesota were formed by glacial action. Many small lakes formed after the glaciers receded and blocks of ice buried in the sediment melted, leaving holes called kettles, that filled with water. Other lakes occupy basins that were scraped out of solid rock by glacial ice. Lake Superior is a prominent example of a lake bottom scoured by glacial ice. Lake Mille Lacs, by contrast, is not a kettle lake or a basin lake. It is considered a Moraine Lake. It was formed as a result of two separate glacial lobes.
Lake Mille Lacs was formed about 15,000 years ago near the end of the last Wisconsin glaciation. A long tongue-shaped lobe of ice called the Superior Lobe flowed into the area from the northeast. This ice carried sediment derived from rock along the Superior basin and the North Shore, which was later deposited beneath the ice and its margin. At its maximum the Superior lobe extended beyond Minneapolis to the south and St. Cloud to the west. Its decline was punctuated by several minor readvances such as the one that deposited the Mille Lacs moraine. About 12,000 years ago another lobe of ice advanced from the northwest and overrode the northern part of the Mille Lacs moraine sending its meltwater into Lake Mille Lacs. |
| Understanding How Glacial Advances |
| Create Moraines |
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End moraines, or terminal moraines, are ridges of unconsolidated debris deposited at the snout or end of the glacier. They usually reflect the shape of the glacier's terminus. Glaciers act much like a conveyor belt, carrying debris from the top of the glacier to the bottom where it deposits it in end moraines. End moraine size and shape is determined by whether the glacier is advancing, receding or at equilibrium. The longer the terminus of the glacier stays in one place the more debris will accumulate in the moraine. There are two types of end moraines; terminal and recessional. Terminal moraines mark the maximum advance of the glacier. Recessional moraines are small ridges left as a glacier pauses during its retreat. After a glacier retreats the end moraine may be destroyed by post-glacial erosion.
Looking at the diagram above you will notice the proglacial lake and the end moraines and terminal moraines formed by the glacier. |
| Lake Mille Lacs |
| Logging Requirements Below |
To claim credit for this cache please answer the following questions. 1. Which sides of the lake are moraines? 2. Which shore has the higher elevation? 3. How is the water level maintained? 4. What is the elevation at the site? 5. Pic encouraged but not required.
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