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Why is the deepest part of a bedrock valley not always directly beneath its river?
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valley
The rugged Atlas Mountains surround a valley in Morocco.
The deepest part of a bedrock valley is often not directly beneath the river due to several geological and hydrological factors.
In many cases, the actual configuration of the valley floor is obscured by valley-fill deposits. When information is available through drilling or geophysical techniques, it reveals that the deepest point is frequently offset from the current river channel. Common reasons for this include:
- Tributary Junctions: The influx of sediment load from a tributary can force the main river to shift toward the opposite side of the valley.1
- Channel Asymmetry: In valleys without thick deposits, the bedrock floor may develop an asymmetrical shape. The deepest part often occurs on the inside of bends, though this depends on the river's sediment load and velocity; if the river cannot entrain its sediment, incision may instead occur on the outside of the bend.1
- Historical Positioning: In straight reaches, the deepest part is often associated with an inner channel cut into the bedrock, which reflects the river's position at the time it flowed at the level of the valley floor.1