Knobs and Kettles EarthCache
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In order to count this Earthcache as a find, you must complete the following tasks and email the answer to me.
1. What is the elevation?
2. Estimate the height of the knobs.
3. Describe the kettles at this location.
Glaciers wreaked havoc in North America in their 2.1 million years of comings and goings. In northeastern South Dakota, they left quite a mess from their mischievous meanderings.
A glacier is a large, long-lasting mass of ice that moves as a result of its weight. A glacier can develop in any area where, over a period of years, more snow accumulates than melts. Ice forms by the compaction and recrystallization (hardening) of the snow. When the mass of ice reaches a certain thickness, it starts to spread out or move away from the area of accumulation. At this point, the ice mass is called a glacier.
The ice within an active glacier is always on the move. Individual ice particles enter the glacier in the accumulation zone and are transported over time to areas where the ice is lost through melting or other processes. The glacier will advance (move forward) when there is more accumulation of ice than what is melting. Conversely, the glacier will retreat (or move back) when there is more melting than accumulation of ice.
Glaciers are very effective at rearranging earth materials. Rocks ranging in size from the finest powder to boxcar-sized boulders have been eroded, transported, and deposited by glaciers. Even larger slabs of rock, up to one mile in length, can be shown to have moved under the influence of glaciers. When the glacier melts, sediment is released from the ice. A variety of sediment types are deposited by glaciers. Till is the term used to describe unsorted glacial sediment. In South dakota, tills contain a large amount of clay- and silt-sized particles, as well as sand and scattered larger rock fragments. When water from melting ice interacts with the sediment, a number of “sorted” sediments result. Sand and gravel deposits (outwash) result when meltwater removes finer silts and clays. Fine-grained sediments are deposited when meltwater becomes ponded in lakes or slower moving sections of meltwater streams.
Evidence of glacial activity in South Dakota can be seen throughout the eastern half of the state. Glacial features can be divided into two basic types, erosional or depositional, and range in size from very small scratches on rocks to features as large as the Coteau des Prairies and the Missouri River. Accumulations of up to 875 feet of glacial sediments are found in parts of the state, while in other areas, glacial erosion has laid bare the underlying bedrock.
Erosional evidence of glacial activity is best illustrated by the many small scratches (striations) found on boulders and rock outcrops that were overridden by the glaciers. Most of the major streams and rivers in eastern South Dakota occupy channels originally cut by meltwater streams originating from melting glaciers. In addition, the broad valleys of the James and Minnesota Rivers owe their shape to the erosive power of glaciers that once occupied these lowlands.
Features that result from the deposition of glacial sediments include nearly all of the hills and ridges in eastern South Dakota. The term “moraine” refers to any accumulation of glacial sediment deposited by the ice, and occurs in many forms, such as knobs. Large blocks of ice are often trapped within glacial deposits. When they eventually melt, a depression is formed in the deposit. Lakes are formed when these depressions (kettles) fill with water.
The landscape here is an example of knob and kettle topography. The mounds or knobs that you see are the result of debris and deposits laid down at the edge of a glacier. The depressions of the knobs (the space in between the hills) are known as kettles. Not always, but many times, you will see these kettle depressions filled with water.
NOT A LOGGING REQUIREMENT: Feel free to post pictures of your group at the area or the area itself - I love looking at the pictures.
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