1. Weathering: The boulder is first broken down by weathering, which can be caused by:
* Frost wedging: Water seeps into cracks in the boulder and freezes, expanding and putting pressure on the rock. This repeated freezing and thawing can eventually break the boulder apart.
* Abrasion: Wind or water carrying sand and other particles can scour the surface of the boulder, gradually wearing it down.
* Chemical weathering: Rainwater, especially acidic rainwater, can dissolve some minerals in the boulder, weakening it and making it more susceptible to breaking.
2. Erosion: Once the boulder has been weakened by weathering, it can be broken into smaller pieces by erosion. Erosion is the process of moving weathered material from one place to another. This can be caused by:
* Wind: Wind can carry small particles of sand and dust, which can bump against the boulder, slowly wearing it down.
* Water: Moving water, like rivers and streams, can carry larger sediment, which can also wear down the boulder. Strong currents can even move large rocks, breaking them up as they bounce along the bottom.
* Glaciers: As glaciers move, they can pick up rocks and boulders, and grind them against the ground and other rocks, eventually breaking them into smaller pieces.
3. Deposition: The smaller pieces of the boulder, now in the form of gravel, pebbles, and sand, are carried by the wind, water, or glaciers and deposited in a new location.
4. Continued Cycle: This process of weathering, erosion, and deposition continues over long periods, slowly turning large boulders into smaller and smaller pieces, eventually ending up as sand or silt.
In short, deposition doesn't directly break down boulders, but it is an essential part of the overall process that leads to the formation of pebbles from larger rocks.
