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Why does glacial outwash become finer farther from the glacier margin?

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esker: Nunavut — glacial landform Eskers, or narrow ridges of gravel and sand left by a retreating glacier, wind through western Nunavut, Canada, near the Thelon River.

Glacial outwash becomes finer farther from the glacier margin primarily due to the loss of stream velocity and the resulting decrease in transporting power.123

As meltwater streams emerge from the glacier, they are typically laden with a wide range of debris sizes. Near the glacier terminus, the flow is often rapid, allowing the water to transport and deposit larger, heavier materials such as boulders and coarse gravel. As the water moves away from the glacier, the stream gradient typically becomes more gentle, causing the flow velocity to decrease.1342

Because a stream's ability to carry sediment is directly tied to its velocity, this reduction in speed forces the current to drop its heaviest load first. Consequently, larger particles are deposited closest to the ice margin, while smaller grain sizes—such as sand, silt, and clay—remain suspended in the water for longer periods and are carried over greater distances before settling. This sorting process results in the characteristic downstream thinning and fining of outwash deposits.1432