Sediment mainly comes from the erosion and weathering of existing rocks and organic material, transported by natural forces like water, wind, gravity, and ice, and then deposited in new locations. The sources can be broadly grouped as follows:
- Land-derived (terrigenous) sources
- Weathering and erosion of rocks on cliffs, hills, and riverbanks.
- Mass wasting processes such as landslides, rockfalls, and mudflows.
- Runoff and soil erosion from agricultural land, forests, and urban areas.
- Glacial grinding and supraglacial melt contribute fine sediment in glaciated regions.
- Biological and chemical sources
- Accumulation of skeletal fragments, shells, and other remains from organisms in marine and freshwater settings.
- Organic detritus from plants and algae that break down and become sediment.
- In-channel and nearshore processes
- Sediment produced within rivers and streams (fluvial sediment) from upstream erosion.
- Nearshore, coastal, and offshore processes redistribute and rework sediments from beaches, bars, and shelves.
- Long-distance transport and deposition
- Rivers transport sediment from inland sources to rivers mouths and into oceans or seas.
- Wind can mobilize and deposit fine sediments (dust, sands) in arid regions or deserts and into terrestrial and marine environments.
Key points to remember
- The most significant source for many coastlines is rivers carrying land-derived sediment to the sea, though local geology and climate can shift the balance toward coastal erosion, glacial material, or biological productivity depending on the region.
- Sediment types vary with source material: mineral grains from rock weathering, clay and silt from fine weathering products, and organic-rich material from biological activity.
- In marine settings, deposition occurs in environments such as beaches, deltas, estuaries, shelves, and deep basins, with the grain size and composition reflecting the balance of supply and energy in the system.
