Sediment
Sediment
Sediment, a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transportedby the action of wind, water, or ice, and/or by the force of gravity acting on the particle itself.
Sediments are most often transported by water (fluvial processes), wind (aeolian processes) and glaciers. Beach sands and river channeldeposits are examples of fluvial transport and deposition, though sediment also often settles out of slow-moving or standing water in lakes and ocean dunes and loess are examples of aeolian transport and deposition. Glacial moraine deposits and till are ice-transported sediments.
Classification
Sediment can be classified based on its grain size and/or its composition.
[edit]Grain size
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Sediment size is measured on a log base 2 scale, called the "Phi" scale, which classifies particles by size from "colloid" to "boulder".
| φ scale |
Size range (metric) |
Size range (inches) |
Aggregate class (Wentworth) |
Other names |
|---|---|---|---|---|
| < -8 | > 256 mm | > 10.1 in | Boulder | |
| -6 to -8 | 64–256 mm | 2.5–10.1 in | Cobble | |
| -5 to -6 | 32–64 mm | 1.26–2.5 in | Very coarse gravel | Pebble |
| -4 to -5 | 16–32 mm | 0.63–1.26 in | Coarse gravel | Pebble |
| -3 to -4 | 8–16 mm | 0.31–0.63 in | Medium gravel | Pebble |
| -2 to -3 | 4–8 mm | 0.157–0.31 in | Fine gravel | Pebble |
| -1 to -2 | 2–4 mm | 0.079–0.157 in | Very fine gravel | Granule |
| 0 to -1 | 1–2 mm | 0.039–0.079 in | Very coarse sand | |
| 1 to 0 | 0.5–1 mm | 0.020–0.039 in | Coarse sand | |
| 2 to 1 | 0.25–0.5 mm | 0.010–0.020 in | Medium sand | |
| 3 to 2 | 125–250 µm | 0.0049–0.010 in | Fine sand | |
| 4 to 3 | 62.5–125 µm | 0.0025–0.0049 in | Very fine sand | |
| 8 to 4 | 3.9–62.5 µm | 0.00015–0.0025 in | Silt | Mud |
| > 8 | < 3.9 µm | < 0.00015 in | Clay | Mud |
| >10 | < 1 µm | < 0.000039 in | Colloid | Mud |
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