How does an oxbox lake form?

Answer 1

An oxbow lake is formed by the rerouting of a river, usually by natural means. A river chooses its path by following the natural low areas of a terrain. Over the course of time, it then carves out that path, through the scouring action of the moving water, more deeply and broadly. Rivers also have bends and turns as they go around areas of higher elevation, like hills and plateaus.

Sometimes, however, a river experiences a high water (flooding) event. When this happens, the increased flow can actually carve out a new channel for the riverbed outside of the original channel. If the flow has been aggressive enough to carve this channel deeply, as the floodwaters recede the river may then continue in its new channel, while the trapped water that was contained in the looped portion remains as a landlocked lake. These are called "oxbow" lakes because they are the shape of the portion of the harness that was placed on the neck of a team of oxen in order to pull a cart (the oxbow).

Ox-bow Lakes are formed (from geobytesgcse.blogspot.com)

1) As the outer banks of a meander continue to be eroded through processes such as hydraulic action the neck of the meander becomes narrow and narrower.

2) Eventually due to the narrowing of the neck, 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.

3) Deposition gradually seals off the old meander bend forming a new straighter river channel.

4) Due to deposition the old meander bend is left isolated from the main channel as an ox-bow lake.

5) 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.

Answer 2

An Oxbox Lake forms a cresent.

ANS2:

(The directions in this description presume an oxbow on the west side of a south-flowing river. Change the relative directions as necessary.)

The oxbow forms because the water's momentum carries it south, into the east bank of a growing meander. That causes the bend in the meander to erode on the east side of the bend, beginning the oxbow. The river, reflected by the east bank, erodes the west bank and broadens the belly of the bend, causing the river channel to migrate west.

As the water stream finishes the ever increasingly broad bend, it is directed back towards the east bank and drops sediment at the west bank. After the entry and exit points eventually merge, the main channel of the stream takes that path of least resistance and sediment blocks off the entry and exit of the oxbow. That results in the crescent-shaped lake being formed adjacent to, and west of, the stream.