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How do deltas form where meltwater streams enter glacial lakes?
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glacial landform
Eskers,
or narrow
ridges of
gravel and sand left by a retreating glacier,
wind through western
Nunavut, Canada, near the Thelon River.
When a meltwater stream enters a standing body of water, such as a glacial lake, it is forced to deposit its sediment load, creating a delta. The formation process involves three distinct layers of deposition:1
- Foreset beds: Coarser materials, such as sand and gravel, are deposited directly at the stream's mouth as successive, steeply inclined layers.1
- Bottomset beds: Finer materials, including silt and clay, are carried farther into the lake by the current and settle as nearly flat-lying layers.1
- Topset beds: As the delta builds outward into the lake, the stream deposits a thin, subhorizontal veneer of gravelly material over the foreset units.1
This foreset-topset complex often forms a triangular shape with the stream mouth at the apex. Over time, these structures can become significant features in the landscape, and many sand and gravel pits are located within the deltas of former glacial lakes.1