The ocean floor near the base of rivers

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The discussion centers on the observation of canyons at the base of large rivers on the ocean floor, which appear to have been carved by river activity. This phenomenon raises questions about the geological history of ocean floors, suggesting they may have been above sea level in the past. Two primary theories explain the formation of these underwater canyons: the first posits that they were shaped by river erosion when the land was above water, while the second attributes their creation to turbidity currents, which are underwater landslides that can extend significantly deeper than known sea levels during ice ages. It is likely that a combination of both processes contributed to the current landscape of the ocean floor.
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When I look at a map which shows the sea floors I see canons at the base of large rivers which tend to fork out and travel long across the ocean floor. It looks very much like they were carved by the river. What are these and what caused them?
 
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Yes You're right indeed. Would it be an idea that those ocean floors were above sealevel in the geologic past?
 
The other main theory is that turbitidy currents (underwater landslides) are mainly responsible for their erosion, as some extend far deeper then sea level has ever been known to fall to during ice ages (3000m below the surface). In reality, a combination of the two may be responsible.

http://www.madsci.org/posts/archives/may2001/988903442.Es.r.html
 

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