Cactus Hills EarthCache
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In order to count this Earthcache as a find, you must complete the following tasks and email the answers to me.
1. How many periods of glaciation did early geologic research indicate there were during the ice age?
2. Where can other remnants of the original glacial deposit be found in the area?
3. What town does the series of kames the Cactus Hills are part of extend toward?
4. Describe the appearance of the Cactus Hills.
This earthcache is located at Great Bear Park in Sioux Falls. In the winter months, Great Bear offers skiing, snowboarding, and tubing down the Cactus Hills. The park is also open during the summer for those who wish to hike on the hills.
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 of the snow. Recrystallization is a process that occurs under situations of intense temperature and pressure where the atoms and molecules of the snow are packed closer together, creating a new crystal structure (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 rocks, up to a mile in length, can be shown to have moved under the influence of glaciers. Sediment is released from the ice when the glacier melts.
A variety of sediment types are deposited by, or are the result of, glaciers. Till is the term used to describe unsorted glacial sediment. In South Dakota, till contains 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. Loess is the term used to describe sorted fine-gained glacial sediment deposited by wind action.
There are fourteen recognized glaciation episodes in North America. Of these fourteen episodes, deposits from five of the episodes can be found in Minnehaha County. From the earliest to the most recent, these episodes are called Pre-Illinoian 1, 2, and 3, Illinoian, and Late Wisconsin.
The Cactus Hills are composed of sand and gravel deposits left more than 300,000 years ago by streams flowing from a receding pre-Illinoian glacier. These deposits mark the point where the ice front stalled before continuing its retreat. Originally, the outwash deposits were more extensive, but later erosion by the late Wisconsin meltwater removed much of the original deposit. The Cactus Hills are remnants of the original glacial deposit.
Geologically, the Cactus Hills are part of a series of kames. A kame is an irregularly shaped hill or mound that is composed of sand, gravel, and till that builds up in a depression on a retreating glacier. The sand, gravel, and till mixture is then deposited on the land surface with further melting of the glacier.
Glacial deposits are important in South Dakota for a variety of reasons. Much of the drinking water used in the eastern part of the state is ground water. The source aquifers for drinking water wells are most commonly saturated bodies of sand and gravel (outwash) deposited by the glaciers. Sand and gravel used in road building and other construction projects are also provided by outwash bodies. The rich soils in eastern South Dakota are derived from till, which consists of ground up, nutrient-rich, rock fragments carried to the area by glaciers. Finally, many of the recreational activities and tourism in eastern South Dakota are centered around rivers and lakes, which originated during glacial episodes.
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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