Oxbow Lakes at Southwestway Park EarthCache
Oxbow Lakes at Southwestway Park
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An oxbow is a severe bend in a river that will create a “U” shape and leaves a very narrow strip of land between the two bends. A lot of times, erosion will wear through this narrow strip and the course of the river changes leaving a “U” shaped or oxbow lake or a dry riverbed.
Meander Formation
Meanders form due to the greater volume of water carried by the river in lowland areas without much change in elevations, which in return results in sideways erosion being more dominant than vertical erosion. This will cause the channel to cut into its banks forming meanders.
1. Water will flow faster on the outer bend of the river where the channel is deeper and there is less friction. This is due to water being flung towards the outer bend as it flows around the meander. This will cause greater erosion and deepen the channel. This sideways erosion results in undercutting of the river bank and the formation of a steep sided river cliff.
2. The inner bend water is slower and will deposit materials in a shallower channel. This increased friction slows the water flow and will have even more depositing. Material builds up on the inner bend; this is called a slip-off slope.
A meander will gradually change its shape and migrate across the floodplain. Meander bends becomes pronounced due to further sideways erosion and eventually an oxbow lake may form.
Oxbow Lake formation
- As the outer banks of a meander continue to be eroded, the neck of the meander becomes narrow and narrower.
- Eventually the two outer bends meet and the river cuts through the neck of the meander. The water now takes its shortest route rather than flowing around the bend.
- Deposition gradually seals off the old meander bend forming a new straighter river channel.
- Due to deposition the old meander bend is left isolated from the main channel as an ox-bow lake.
- Over time this feature may fill up with sediment and may gradually dry up (except for periods of heavy rain). When the water dries up, the feature left behind is known as a meander scar.
The bedrock surface in Marion County is composed of Paleozoic stratigraphic units ranging from Silurian to Mississippian age including shales , siltstones , sandstones , limestones , and dolostones .
This image shows the Surficial Geology of the area.
The dotted area with the larger dots mixed in is Sand- and gravel-dominated.
the dotted area is a mix of sand- gravel and till.
the white area is till
The red, green and black checked areas are isolated pockets with higher concentration of till, sand, and gravel
The image above shows the Hydrogeology of the the shallow aquifer system.
The light blue area is composed of Interbedded sand and gravel till.
The red area is unconfined sand and gravel with scattered till.
The green is Hummocky ridges of sand/gravel and till.
The off white area in the green is a small valleys formed in till with some sand/gravel.
Submit answers to the following questions.
1. What is the approximate length of the oxbows?
2. Explain the differences in the appearance of the inner bend and outer bend of the White River oxbow.
3. What signs of erosion are evident? What signs of depositing are seen?
4. Based upon the geological images above do you think the suface geology played a role in the formation of the oxbow?
Info sources: brcross95
igs.indiana.edu/
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