Flat River Glacial Imprints EarthCache
Flat River Glacial Imprints
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Difficulty:
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Terrain:
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Size: 
(large)
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When mastadons roamed lower Michigan, as recently as 10-20,000 years ago, the last glaciers of the Pleistocene Epoch were receding from this area. These glaciers are responsible for the shape of the landscape you see and for the types of sediment under your feet. The effects of the glaciation are still evident. The rolling, hilly moraines, flatoutwash plains, and kettle lakes are typical features in the watershed.
As a glacier advances across land, it plucks, grinds, and scrapes huge amount of rock and seidment from its path. This hoard of debris from different regions is thoroughly mixed and crushed within the slowly moving ice. Eventually, the glacier melts away, leaving behind a load of sand, gravel, and rocks.
If you dig under the soil in this area, you would find two main types of glacial deposits. In high ground surrounding the valley, the last receding glacier dropped a jumbled up mix of sand, gravel and rocks, called "Glacial till". In the Flat River valley, flowing meltwater from the glacier sorted the deposits into layers called "Glacial outwash".
Glaciers contain large amounts of silt and sediment, picked up as they erode the underlying rocks when they move slowly downhill. At the front of the glacier, meltwater can carry this sediment away from the glacier and deposit it on a broad plain. The material in the outwash plain is often sorted by size as the water runs off of the melting glacier with the finest materials, like silt, being the most distantly re-deposited, whereas larger boulders are the closest to the original terminus of the glacier. An outwash plain might contain surfacial braided stream complexes that rework the original deposits. They may also contain kettle lakes, locations where blocks of ice have melted, leaving a depression that fills with water.
Glacial striations on rock Glacial till is unsorted glacial sediment. It is that part of glacial drift which was deposited directly by the glacier. Its content may vary from clays to mixtures of clay, sand, gravel and boulders. This material is mostly derived from the subglacial erosion by the moving ice of the glaciers of previously available sediments. Bedrock can also be eroded through the action of glacial plucking and abrasion and the resulting clasts of various sizes will be incorporated to the glacier's bed. Eventually, the sediment forming this bed will be abandoned some distance down-ice from its various sources. This is the process of glacial till deposition. When this deposition occurs at the base of the moving ice of a glacier, the sediment is called lodgement till.
In order to get credit for this Earthcache, please email the answers to the following questions:
- What type of Glacial deposit are you standing on?
- What is the difference between Glacial Till and Glacial Outwash?
- Do you see any types of glaciation in the Flat River Watershed around you? If so which?
We always enjoy seeing photos taken of the cache location attached to logs (but that is completely optional).
While the location of this Earthcache is wheelchair & stroller accessable (it's on a paved trail), there is a somewhat long hill down into the valley.
Sources:
Fallasburg Park Info Kiosk
Wikipedia: Glacial Till
Wikipedia: Glacial Outwash
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