Reshaping Earth's Surface
The surface of the Earth may seem solid and permanent, but it is constantly being changed by a set of powerful natural processes. These processes can be grouped into three main categories: weathering, erosion, and deposition.
Weathering: Breaking It Down
Weathering is the process that breaks down rocks and other materials on the Earth's surface into smaller pieces. The key thing to remember about weathering is that it happens in situ, meaning 'in place'. It does not involve any movement of the broken material.
There are two main types of weathering:
Mechanical Weathering (or Physical Weathering): This is the physical breakdown of rocks into smaller fragments without changing their chemical composition.
Example: Frost Wedging. Water gets into cracks in a rock, freezes, expands, and forces the crack to get bigger. This repeated freezing and thawing can split large rocks apart.
Chemical Weathering: This is the breakdown of rocks through chemical reactions. The minerals in the rock are changed into new substances.
Example: Oxidation. Oxygen in the air reacts with iron in rocks to form iron oxide, or rust. This weakens the rock and gives it a reddish-brown color.
Example: Carbonation. Carbon dioxide in the air dissolves in rainwater to form a weak acid (carbonic acid). This acid can dissolve rocks like limestone, creating caves and sinkholes.
Erosion: Carrying It Away
Erosion is the process that moves the weathered rock fragments (called sediment) from one place to another.
The main agents of erosion are:
Water: Moving water in rivers and streams is the most significant agent of erosion on Earth. It can carry huge amounts of sediment and carve deep canyons over time (like the Grand Canyon).
Wind: Wind can pick up and transport sand and dust, especially in dry areas. This can wear away rock surfaces in a process similar to sandblasting.
Ice: Glaciers are massive, slow-moving rivers of ice. As they move, they can pluck and scrape away huge amounts of rock and soil, carving out valleys and shaping mountains.
Gravity: Gravity can cause the downslope movement of rock and soil in events called mass wasting, such as landslides and rockfalls.
Deposition: Dropping It Off
Deposition is the process in which sediment is laid down or dropped in new locations. Deposition occurs when the agent of erosion (water, wind, or ice) slows down and loses its energy, and can no longer carry its load of sediment.
Landforms created by deposition:
Deltas: A fan-shaped deposit of sediment at the mouth of a river where it enters a lake or ocean.
Beaches: An accumulation of sand and other sediments deposited by waves along a coastline.
Sand Dunes: Hills of sand deposited by the wind.
Moraines: Ridges of rock and sediment (called till) deposited by a melting glacier.
In short: Weathering breaks it, erosion takes it, and deposition drops it.