What is an Oxbow Lake?
An oxbow lake is a uniquely shaped lake resulting from the path of a meandering river. Oxbow lakes are U-shaped or curved bends in a river that are cut off from the main river flow, forming a lake Generally, no water flows in or out of oxbow lakes. They rely on local rainfall and, over time, can turn into swamps. They ultimately evaporate in just a few years after having been cut off from the main river and turn into wetlands or even fertile land due to aquatic succession.
The Aquatic Succession Process:
How do Oxbow Lakes form?
Once a river begins to curve, the stream begins to move more rapidly on the outside of the curve and more slowly on the inside of the curve. This then causes the water to cut and erode the outside of the curve and deposit the sediment on the inside of the curve. As the erosion and deposition continue, the curve becomes larger and more circular. The outer bank of the river where erosion takes place is known as the concave bank. The name for the bank of the river on the inside of the curve, where sediment deposition takes place, is called the convex bank. Eventually, the loop of the meander reaches a diameter of approximately five times the width of the stream and the river begins to cut the loop off by eroding the neck of the loop. Eventually, the river breaks through at a cutoff and forms a new, more efficient path. Sediment is then deposited on the loop side of the stream, cutting off the loop from the stream entirely. This results in a horseshoe-shaped lake that looks exactly like an abandoned river meander. Such lakes are called oxbow lakes because they look like the bow part of the yoke formerly used with teams of oxen.
The Aging Process of Lakes and ponds:
Bodies of water, like many things on Earth, go through an aging process.
Oligotrophic Lakes (“young lakes”) - Over several thousands of years, shorelines of oligotrophic lakes erode and become less steep. The rocks on the lake bottom grind against each other creating sand, while more plant life emerges on the shore and in the water.
Traits of Oligotrophic Lakes:
- Steep shorelines going down to the water’s edge
- Coniferous trees (pines, etc) around the lake’s shoreline
- They are very deep (100+ feet)
- The lake bottom is mostly rocky
- The water is very clear
Mesotrophic Lakes (“middle-aged lakes”) - After the years go by, mesotrophic lakes gain nutrients from the fallen, decayed leaves from deciduous trees, decayed shoreline plants, decaying aquatic plants, and the remains of fish and other water creatures. The lake bottom near the shore becomes covered with silt and sediment as a result of more years of weathering and erosion.
Traits of Mesotrophic Lakes:
- Less steep shorelines
- A mixture of coniferous and deciduous trees around the lake’s shoreline
- They are less deep than oligotrophic lakes
- The lake bottom is mostly made of sand and/or clay
- The water is very clear
Eutrophic Lakes (“old lakes”) - It is the nature of all lakes to fill themselves in and become land. After many more years, the lake will continue to become shallower in the center, more shoreline will erode into the water, and trees will fall in.
Traits of Eutrophic Lakes:
- Gentle, completely flat shorelines
- Mostly deciduous trees (oaks, maples, etc) around the lake’s shoreline
- They are pretty shallow
- The water is murky
Sources:
https://en.wikipedia.org/wiki/Glacial_lake
https://www.goodbyetomuck.com/wiki/everything-about-muck-in-lakes
https://www.geographyrealm.com/how-oxbow-lakes-form/
https://en.wikipedia.org/wiki/Oxbow_lake
Logging Tasks:
1. Based on what you know in the description and your observations at the GZ, would you consider Gray’s Lake to be an oxbow? Explain your rationale.
2. After observing the lake and its surroundings, determine what type of aging process Gray’s Lake is in currently? Name specific signs of this at the GZ.
3. Predict what will happen in the coming years/decades that will change the appearance of Gray’s Lake.
4. As of June 2019, earthcaches now contain required photo logging tasks. Please provide a photo of yourself, your GPSr, or a personal item that proves that you have visited this site. Please post this in your log.
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