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Earth Cache
1. To learn something about our planet.
2. The lesson that you learn is learned forever.
3. Leave nothing but your footprints behind, and always practice CITO.
A glacial lake is a lake with origins in a melted glacier. They are formed when a glacier erodes the land, and then melts, filling the hole or space that it has created. Near the end of the last glacial period, roughly 10,000 years ago, glaciers began to retreat. A retreating glacier often left behind large deposits of ice in hollows between drumlins or hills. As the ice age ended, these melted to create lakes. When a person thinks about glacial lakes in Iowa the first thought that comes to their mind would be the Great Lakes of Spirit Lake and Okoboji area. That is the process that formed the Great Lakes.
Another type of glacial lake is a kettle lake. One of these is Clear Lake which we will learn more about.
First, we must learn about kettles and how they are formed. A kettle, also called a kettle hole, in geology, is a depression in a glacial outwash drift made by the melting of detached mass of glacial ice that become wholly or partly buried.
Two types of kettles are recognized: a depression formed from a partially buried ice mass by the sliding of unsupported sediment into the space left by the ice or from a depression formed from a completely buried ice mass by the collapse of overlying sediment. By either process, small kettles may be formed from ice blocks that were not left as the glacier retreated but rather were later floated into place by shallow meltwater streams. Kettles may occur singly or in groups. In either case when the ice melts, the hole it leaves behind is a kettle. During this same time, ramparts can form around the edge of the kettle hole. The lakes that fill these holes are seldom more than 33 feet deep and eventually become filled with water, sediment, or vegetation. If the kettle is fed by surface or underground rivers or streams, it becomes a kettle lake. If the kettle receives its water from precipitation, the groundwater table, or a combination of the two, it is termed a kettle pond or kettle wetland, if vegetated.
Clear Lake is a natural spring fed lake with a maximum depth in the main portion of the lake of just over 18 feet and a mean depth of just over 10 feet making this by definition a kettle lake. Most kettle lakes however are small in size in comparison to Clear Lake (under 500 acres) so what may have caused Clear Lake's size?
By what we have learned kettles can occur singly or in groups so it is entirely possible that there were several of these glacial blocks all in the same area and together made Clear Lake what it is. This indeed is a possibility but also just a theory. When you look at a lake map of Clear Lake what the "locals" call Little Clear Lake could also be described as a kettle lake. It is connected to the main lake but man has increased the depth at the point where they connect to each other for navigational purposes. Also, to the south of Clear Lake are many smaller kettle ponds and potholes which lend support to this idea.
However, the largest and most acclaimed kettle lake in Alaska's Denali National Park isn't technically a pure kettle lake. While an ice chunk did help form Wonder Lake's basin the retreating glacier that left it behind also had a hand in carving it out. So it seems more logical that this is the way Clear Lake was formed as well. It has the attributes of a kettle lake with the depth and being spring fed but it is much larger than most true kettle lakes.
So from what we have learned do we really know if Clear Lake is a kettle lake?
I asked this question to the IA DNR and this is their response.
"Typically I would not term Clear Lake as a kettle lake. It was glacially formed. By the definition, I guess you may be able to call Clear Lake a kettle lake, but it would be on the top end for size. Here is the definition of a kettle. -- Kettles are depressions left behind after partially-buried ice blocks melt. Many are filled with water, and are then called "kettle lakes". ... Kettle lake basins were formed as the glaciers receded. While this was happening, a block of ice broke off the glacier, and just sat there. I am not sure if it can be determined if Clear Lake was formed on the advance of the glacier or when it receded."
So there you have it... To Kettle or Not to Kettle, that is the question. Will we ever know the answer?
To log this Earth Cache, you will need to perform these tasks.
If you have a Secchi disk in the trunk of your car you can use that to find the clarity of the lake. However, most geocachers aren't so equipped, so instead, using a clear glass container take a sample of the lake water to examine.
1) Measure and record the ph of the sample. (PH test strips can be found at most pet supply stores)
2) Examine the contents of the glass container and describe what you see, i.e., any sediment, if so to what extent? Is the water indeed clear? Is it cloudy? Any other observations?
3) Send your answers of your findings to me through the cache page.
4) Not required, but it's always nice. Please post a picture of yourself or team with your gpsr and the lake as your background in your online log.
IF ANSWERS ARE NOT SENT YOUR LOG WILL BE DELETED!