Hello, I have a question. The satellite image on the picture shows the delta of

Question

Hello, I have a question.

The satellite image on the picture shows the delta of the Yukon River in the Bering Sea along the coast of Alaska. Explain why the river breaks into numerous channels as it crosses the delta. What term is applied to these chhannels? Notice the cloud of sediment in the water surrounding the delta. Are these sediments more likely sand and gravel or silt and clay? Explain. After the cloud of material settles to the seafloor and the delta expands farther into the Bering Sea, which beds of the delta will these sediments become?

Thanks :)

Explanation / Answer

River breaking into numerous channels happens not only when it is meeting the sea, it also happens when it is meeting a lake or another river altogether. Such river channels are known as ''Distributaries''. These channels are formed in a depositional environment.

How are these distributaries formed?

In the upstream part of the river (i.e in its youth or mature phase), it is observed that it flows throw a single channel. This is because the channel current is persistent in strength and direction. But when it approaches a depositional environment (like sea or lake), the channel loses its strength to carry load (both bed-load and suspended load) and the cureent direction becomes variable.

The load-bearing capacity is reduced due to the river flowing throw extremely low gradients, closer to its base-level. Also the direction of the channel current becomes variable at this juncture due to same reason.

Cloud of sediments surrounding the delta?

The cloud of sediment surrounding the delta is an extremely fine grained sediment of the silt and clay-sized particles. Sand and gravels require strength in the channel currents to be transported. At the deltaic level (at old phase), such strength is rarely observed in rivers. That is why the sediments are mostly finer-grained material.

Which beds of the delta these sediments will become?

As the delta is expanding, the deposited sediments will form foreset beds.

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