A meander scar, occasionally meander scarp, is a geological feature formed by the remnants of a meandering water channel. It is characterized by a crescent-shaped cut in a bluff or valley wall, produced by a meandering stream. They are often formed subsequent to the creation of oxbow lakes.
The formation of oxbow lakes and meander scars.
The meander neck is visible (upper-a), while the cutoff process shows the formation of the oxbow lake (lower-b).
As the oxbow lake fills with sediment, it becomes swampy or marshy (upper-c).
Finally, when the oxbow lake completely fills with sediment (lower-d), it becomes a meander scar.
Image taken from Central Michigan University College of Science & Technology
The term, meander scar, 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. The meander scar below you is a remnant of a meander which is almost completely filled with sediment and is now cultivated as part of the field. The scar can be seen as a slight dpression running through the field and contains vegetation of a slightly different colour than the surrounding plants.
Meanders are caused by the varying velocities of current within the river channel. Due to the higher water current on the outer banks of the river through a bend, more erosion occurs causing the characteristic steep outer slopes of a river valley. While the outer banks are eroding more quickly due to the increased current at that point in the river, the inner bend is increasing in size into the bend due to the slower moving water which deposits sand and gravel along the inner bank. The more the inner deposits increase, the faster the water is forced to flow around the outer bend creating a greater meander in the river. At some point, the meander will become so great that the "meander neck", (the narrowest point of the meander) will be overcome by a spring flood, will be cut through, and the river will return to a straghter line of flow.
The former river path has now become an oxbow lake separated from the river by sediment deposited across the former neck of the meander. In certain habitats, if the scar has sufficient water, or as an oxbow lake fills with sediment, these areas may become marshes or wetlands and continue as such.
Usually, as the oxbow lake continues to fill with decaying vegetation, it will become more and more shallow until it finally disappears and becomes the faint meander scar you see below you.
NOTE: The formation is on private property and should be observed only from the parking area above the field. Please do not enter the property; it is not necessary to do so to answer the questions.
In order to log this cache, please email the cache owner the answers to the following questions: (Please do not post your answers on the cache page. Cachers who have not sent their answers to the CO will have their logs removed.)
1) As you visually follow the curve of the meander through the field and back to the river, approximately how much of the field does the meander scar cover?
2) What is the approximate distance the outer edge of the meander scar was from the river before it was cut off at the meander neck? (Suggestion: you may need to use your GPS cursor to assist in this estimation)
3) The vegetation is a slightly different colour along the whole curve of the meander scar. What would you suggest is the reason for this difference?
4) The whole lower field, including the bluff you are standing on, has an interesting shape. Are there any prehistorical assumptions you can draw from the shape of the field and its proximity to the river?
5) Optional: Please feel free to post a picture of the field as it is viewed in the various seasons.