Minnepejuta EarthCache
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
In order to count this Earthcache as a find, you must complete the following tasks and email the answers to me.
1. What is the elevation?
2. Estimate the size of the lake.
3. Describe the appearance of the lake. What do you think accounts for its appearance?
4. Describe the area surrounding the lake.
As with all lakes in northeastern South Dakota, Medicine Lake was created about 20,000 years ago when glaciers moved across the area. The advancing glaciers carved out parts of the landscape and smoothed out others. When the glacier began its retreat, small chunks of the massive ice sheet broke off and remained stationary until melting. The sheer weight of these small ice chunks sitting in one spot caused the land to sink, creating a depression. As the ice chunk melted, the bowl-shaped depression filled in with the melt water and a lake was born.
Medicine Lake began as a freshwater lake. Today, however, it is a saline lake, which means it is a salt lake (like the Great Salt Lake in Utah).
The biggest factor causing Medicine Lake’s transformation from a freshwater to a salt water lake is the fact that it has lies in an endorheic basin. An endorheic basin is a closed drainage basin that retains water, but does not allow any outflow of water to other bodies of water, such as rivers. Normally, water that has accumulated in a drainage basin eventually flows out through rivers or streams or by underground diffusion through permeable rock. In an endorheic basin, however, rain and other precipitation that falls within the body of water does not flow out. The only way the water leaves the drainage system is by evaporation and seepage through small holes or permeable substances. The bottom (or lowest elevation) of an endorheic basin results in a salt lake.
Water enters Medicine Lake through a chain of lakes and potholes. In the southeast, water travels from McKillicans Lake through Round Lake and Horseshoe Lake and into Medicine Lake. From the northwest, water travels through a series of potholes and ends up in Medicine Lake. During the time the water is moving toward Medicine Lake, it is exposed to evaporation whenever it occupies one of the other lake or pothole basins. As a consequence of this, concentration of the initial water starts in McKillicans Lake and progresses, with more evaporation and concentration occurring each time it is exposed to a different lake basin. This process of evaporation and movement from one body of water to another leaves behind a high concentration of minerals and other inflow erosion products. Over time, this input of erosion products can cause the endorheic lake to become relatively saline (a salt lake). Therefore, Medicine Lake, lying at the lowest elevation in the closed drainage system, receives water that has already been concentrated during its migration through the chain of lakes and potholes. This increases the salinity of the lake. The increased salinity also makes the lake more vulnerable to pollutants.
Geologists also say Medicine Lake has much higher salinity than other lakes in the area because a large mineral water spring feeds the lake on its west side. Since the lake has no outlet, centuries of evaporation have increased the mineral content beyond the point any animal can withstand. Fish cannot survive in the lake’s water. Geese or ducks landing on its surface take flight almost immediately. The water is so mineralized swimmers are unable to sink.
It is said that, on a calm day, newspaper headlines can be read through fifteen feet of the lake’s crystal clear water. Medicine Lake’s healing qualities have been prized as a salve for skin ailments and other diseases. Throughout history, people have traveled from miles around to bathe in its waters. A public beach and swimming area used to be offered at Medicine Lake, but that has long since been closed.
The Sioux called this lake Minnepejuta or “medicine water” - a salt water lake on the prairie.
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.
Additional Hints
(No hints available.)
Treasures
You'll collect a digital Treasure from one of these collections when you find and log this geocache:
Loading Treasures