If you make your approach along the creekbed, take notice of the different layers of shale and sandstone in the exposed cut banks -- you may also see geodes and fossils if you look closely.
A cut bank is an erosional feature of streams. Cut banks are found in abundance along mature or meandering streams, they are located on the outside of a stream bend, known as a meander. They are shaped much like a small cliff, and are formed by the erosion of soil as the stream collides with the river bank. As opposed to a point bar, it is an area of erosion rather than deposition.
Stream Channel Erosion. Stream channel erosion consists of both stream bed and stream bank erosion. Stream bed erosion occurs as flows cut into the bottom of the channel, making it deeper. This erosion process will continue until the channel reaches a stable slope. The resulting slope is dependant on the channel materials, and flow properties. As the stream bed erodes, and the channel deepens, the sides of the channel become unstable and slough off; resulting in stream bank erosion. Stream bank erosion can also occur as soft materials are eroded from the stream bank or at bends in the channel. This type of stream bank erosion results in meandering waterways. One significant cause of both steam bed and stream bank erosion is due to the increased frequency and duration of runoff events that are a result of urban development.
Typically, cut banks are nearly vertical and often expose the roots of nearby plant life. Often, particularly during periods of high rainfall and higher-than average water levels, trees and poorly placed buildings can fall into the stream due to mass wasting events. Given enough time, the combination of erosion along cut banks and deposition along point bars can lead to the formation of an oxbow lake.
Not only are cut banks steep and unstable, they are also the area of a stream where the water is flowing the fastest and the deepest, making them rather dangerous. Geologically speaking, this is known as an area of high-energy.
At this location you will notice that the creek leaves its rocky lined creek bed and enters an area that is composed of soft clay and shale. At this point where it hits this layer the creek makes a large Z pattern as it tries to avoid the harder rocky areas. This is what has caused this particular erosion at this site. Notice where the soft clay has been carved out of the western bank and in the dry season you can see the shale and clay that has accumulated in sand bars opposite the cut bank. This is the only place in the upper creek that this has occurred just before the impoundment of Buffalo Lake.
To log this Earthcache email the answers to the following questions.
1. Where is the deepest water, on the outside or inside of the bend?
2. How can cut banks shorten a plants life?
3. Estimate how high the cut is from the creek bed to the top of the bank?
In addition to those answers please post a photo of yourself and GPS with the cut bank in the background.
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