There are many beach ridges along Lake Michigan, including the Zion Beach Ridge Plain we saw on our field trip. It is located from Kenosha, Wisconsin to North Chicago, Illinois. These beach ridges are formed as the waves deposit a load of sediment along the beach when the lake level is low. A typical beach ridge plain has a ridge, swale, ridge, swale pattern. Each ridge was where the shoreline was at one time.
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This picture shows the beginning stages of a ridge. Over time this ridge will be farther back from the water. |
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This is an aerial photo of the Beach Ridge Plain. You can see how the shoreline along Racine and Kenosha was eroded away, and the plain area was built up.
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Because of the transport and build-up of the sediment, the Pike and Dead Rivers were unable to maintain an open channel to Lake Michigan. They would only be able to reach Lake Michigan at flood stage. Dredging is often used to open these channels. Because of the blockage at the mouth of the Dead River, ponding of the water has taken place. This could be seen as we walked along the Dead River; there was no current and lily pads were present in many places.
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Click to enlarge. |
The mouth of the Pike River can not empty into Lake Michigan because of the build-up of sediment. The river must reach flood stage in order to reach the lake. If you enlarge the photo, you will more clearly see the blockage of the channel.
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| Here also, at the mouth of the Dead River, we could see where the channel can not get through because of the sediment block-age.
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