A grain of sand primarily moves through saltation, a bouncing motion caused by wind.
Here's a breakdown of the ways a grain of sand can move:
Saltation: The Bouncing Journey
Saltation is the dominant method of sand transport, accounting for approximately 95% of sand grain movement. It works as follows:
- Wind Lifts: Wind exerts force on the sand grain, and if strong enough, lifts it into the air.
- Short Hop: The grain doesn't stay airborne for long. Due to gravity, it quickly falls back down.
- Impact: Upon landing, the grain strikes the surface, transferring energy.
- Chain Reaction: The impact can dislodge other sand grains, sending them into saltation as well, creating a ripple effect.
Creep: The Slow Push
Creep is a less common method, responsible for about 4% of sand movement. It relies on impacts from other grains:
- Collision: Larger sand grains, or even small pebbles or clay particles already in motion (often due to saltation), collide with stationary sand grains.
- Energy Transfer: The force of the impact transfers kinetic energy to the resting grain.
- Slight Movement: This transferred energy causes the resting grain to move slightly, typically rolling or sliding along the surface. Creep is a much slower process than saltation.
Suspension: Rarely Airborne
While less common for typical sand grains (which are relatively heavy), very fine sand or dust particles can be suspended in the air and transported over significant distances. This is more characteristic of silt or clay, not coarse sand. Suspension accounts for a very small percentage of the overall movement of material typically considered "sand."
Summary Table
| Movement Type | Percentage of Sand Movement | Description |
|---|---|---|
| Saltation | ~95% | Bouncing motion caused by wind lifting and impacting sand grains. |
| Creep | ~4% | Movement caused by collisions with other grains, resulting in rolling or sliding. |
| Suspension | ~1% or less | Very fine sand or dust particles carried long distances by wind. |
In conclusion, the primary way a grain of sand moves is through saltation, followed by creep, with suspension being rare for typical sand grain sizes.
