Page 507 - Geosystems An Introduction to Physical Geography 4th Canadian Edition

15.2a
STREAM MEANDERING PROCESSES
Over time, stream meanders migrate laterally across a stream valley, eroding the outside of bends and filling the insides of bends. Narrow areas between meanders are necks. When discharge increases, the stream may scour through the neck, forming a cutoff, as seen in the photograph.
Stream valley landscape:
A neck has recently been eroded, forming a cutoff and straightening the stream channel. The bypassed portion of the stream may become a meander scar or an oxbow lake.
15.2b
Direction of flow
Cutoff
FORMATION OF AN OXBOW LAKE
Neck
Itkillik River in Alaska [USGS.]
The neck narrows even more due to undercutting of its banks.
Undercut bank
The diagrams below show the steps often involved in forming an oxbow lake; this photo corresponds to Step 3, the formation of a cutoff. As stream channels shift, these processes leave characteristic landforms on a floodplain.
Step 1:
A narrow neck is formed where a lengthening meander loops back on itself.
Neck
Stream meander
The stream erodes through the neck, forming a cutoff.
Cutoff
Follow up: In your own words, describe the sequence of steps in the process that forms an oxbow lake.
Animation
Stream Processes, Floodplains, Oxbow Lake Formation
Step 2:
Step 3:
Point bar
Step 4:
An oxbow lake forms as sediment fills the area between the new stream channel and its old meander.
Oxbow lake
GEOquiz
471
1. Explain: Explain the processes that cause a gentle bend 2. Summarize: Summarize the process by which a stream, over along a stream to become a deeply looping meander. time, could produce the landscape in the GIA 15.2a photograph.
geosystems in action 15 MEAnDERInG STREAMS