River Bends Meander Scar EarthCache
Hidden : 6/13/2012
Difficulty:
2 out of 5
Terrain:
3 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:


A meander scar is a geological feature formed by the remnants of a meandering water channel. They are characterized by a crescentic cut in a bluff or valley wall, produced by a meandering stream.

They are often formed during the creation of oxbow lakes. The term itself may refer alternatively to the actual cuts into the bank of a bluff, or to the general feature of a drying or dried meander. Both uses, however, describe features of the same process.

Meander scars are caused by the varying velocities of current within the river channel. Due to higher velocity current on the outer banks of the river through the bend, more erosion occurs causing the characteristic steep outer slopes. In certain habitats, if the scar has sufficient water, or as an oxbow lake fills with sediment, these areas may become marshes or wetlands.


A point bar, or slip off slope is a depositional feature of streams. Point bars are found in abundance in mature or meandering streams. They are crescent-shaped and located on the inside of a stream bend, being very similar to, though often smaller than towheads, or river islands.

Point bars are composed of sediment that is well sorted and typically reflects the overall capacity of the stream. They also have a very gentle slope and an elevation very close to water level. Since they are low-lying, they are often overtaken by floods and can accumulate driftwood and other debris during times of high water levels. Due to their near flat topography and the fact that the water speed is slow in the shallows of the point bar they are popular rest stops for boaters and rafters. However, camping on a point bar can be dangerous as a flash flood that raises the stream level by as little as a few inches (centimetres) can overwhelm a campsite in moments.

A point bar is an area of deposition whereas a cut bank is an area of erosion.

Point bars are formed as the secondary flow of the stream sweeps and rolls sand, gravel and small stones laterally across the floor of the stream and up the shallow sloping floor of the point bar.


A cut bank also known as a river cliff, 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 which is an area of deposition, a cut bank is an area of erosion.

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.

Material eroded here is deposited downstream in point bars.

meander



Here you will see a screenshot of the aerial view of the meander scar. Although it looks like it is an active oxbow, the water is dried up for nearly all of the scar. This means that this is a relatively young meander scar, and the process has occurred within the last year or so.

The first arrow points to the point bar of the meander scar. When you enter the island, you will notice that the point bar here is much bigger than those of active river meanders. The crescent shape is still present.

The second arrow points to the cut bank. You can tell even from the aerial photo that this meander was a tight turn, this caused the cut bank to gain even more height than usual. Indeed, the most standing water that is contained in this meander scar is that closest to the river cliff.


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To log this earthcache as a find you must complete these tasks:

1.) Go to Reference Point 1 (N 42° 37.943 W 083° 02.533). Take an elevation reading.

2.) Go to Reference Point 2 (N 42° 37.922 W 083° 02.549). Take an elevation reading. How many feet would the river have to rise to completely flood the island? Send me the answer to this and the elevation of this second reference point.

3,) How deep is the water of the deepest point in the Meander Scar? You may have to use a stick to find out. Post this in your online log so we can keep track of the water depth.

4.) Examine the soil of the point bar (slip off slope). How is it different from the soil of a point bar of an active meander? Email me your findings.

5.) Estimate the height of the River Cliff (cut bank). Email me the answers.

6.) (Optional) Take a picture somewhere on the island and post it in your online log.

Additional Hints (No hints available.)



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