Turtle Mountain was the first land in Manitoba to emerge from the 2-3 km-high ice sheet that covered the area during the Late Wisconsinan glaciation, some 12,800 years ago. As the ice melted, streams of meltwater would carry sediment from the glacier out onto the land below. This fast-flowing meltwater would slow as it emerged from under the ice, and the loss of velocity would cause sediment to be deposited. This type of deposit is called outwash. Characteristic of outwash plains is a feature known as kettles. Kettles are depressions in the ground that form when large chunks of ice fall off the glacier and are overwhelmed with outwash or buried by till. As the outwash or till settles, the buried ice slowly melts, causing the new ground above it to shift and sink, forming the kettle holes. The graphic below demonstrates this process.
When kettles are filled with water, they are known as kettle lakes. The Turtle Mountain plateau, especially the portion in the provincial park of the same name (a few miles west), is home to hundreds of kettle lakes. These lakes may take many shapes, but are commonly small and relatively circular. These are often called “pothole lakes”. Having formed as a result of ice blocks melting, they tend to be small, shallow, and without an abundant source of replenishing water aside from precipitation and runoff. As a result, these lakes are susceptible to drought and colonization by plants. Aquatic plants take root and encroach on the edges of the wetland. As these plants grow, die, and decompose, organic soil accumulates, allowing more types of plants to colonize the space. Over millennia of fluctuating precipitation levels and the plants’ life cycles, these lakes may dry out entirely and become meadows. The Disappearing Lakes Trail in the western part of Turtle Mountain Provincial Park allows you to observe the effects of this wetland-to-meadow succession.
Sources
- Bloom, A. 1978. Geomorphology: a systematic analysis of Late Cenozoic landforms. Prentice-Hall, Inc. Englewood Cliffs, NJ. 399-401 pp.
- Author Unknown. 2011. Kettle Hole. (17 May 2011). <http://www.landforms.eu/cairngorms/images/kettle-hole.gif>. Accessed November 13, 2013.
- Disappearing Lakes Trail interpretive signage, Manitoba Conservation and Water Stewardship (special thanks to MCWS Head of Interpretation, Sloan Cathcart).
- https://www.gov.mb.ca/sd/pubs/parks-protected-spaces/management_plan/turtle_mountain_management_plan.pdf
- https://www.gov.mb.ca/sd/pubs/parks-protected-spaces/park_info/turtle_mountain_pp.pdf
- http://vantagepoints.ca/stories/turtle-mountain/
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To log this earthcache as found, first e-mail me the answers to the following questions (don’t post them in your log!). You may log it as found without hearing a response from me, but e-mails with missing or poor answers to the first four questions may be deleted, and the cacher notified as to the reason(s) why.
1. When glaciers transport larger boulders across great distances and deposit them in new locations, those boulders are known as erratics. There is an erratic near the posted coordinates. What is the approximate height and length of the erratic?
2. The most challenging part of the hike is the final rise to the summit. Calculate the slope of this rise by marking a waypoint at the “summit” sign (pictured above) and another one when you reach the summit itself (at the foot of the tower). Express your answer as either a percentage or in degrees (or both, if you want). This website can help you do the math.
3. According to the base of the viewing tower, how high does “The Turtle’s Back” rise above Lake William?
4. Look south from the top of the viewing tower. In the distance you can see a pothole lake, and beyond that Charlton Lake, which is larger and more irregularly shaped. Observe how much the pothole lake has shrunk from its historic size (look at the surrounding treeline). How much of that space has already succeeded into a meadow? Do you think the same thing will happen to Charlton Lake?
5. (Optional) Post a photo at the summit, with either the tower or the benchmark visible. (The benchmark is very easy to spot (and you could log it until January 2023), although it has changed since the area was originally surveyed.)
