1. Mechanical Weathering:
* Frost Wedging: Water seeps into cracks in the rock, freezes and expands, putting pressure on the rock. This repeated freezing and thawing cycle can eventually break the rock apart.
* Thermal Expansion and Contraction: Rocks expand when heated and contract when cooled. This daily cycle, especially pronounced in deserts, can cause stress on the rock and lead to fracturing.
* Abrasion: Windblown sand and pebbles can scour rock surfaces, gradually wearing them down. Moving glaciers and streams can also cause abrasion.
* Root Wedging: Tree roots can grow into cracks in the rock, exerting pressure as they expand and ultimately breaking the rock apart.
2. Chemical Weathering:
* Dissolution: Some minerals in rocks, like limestone, are soluble in water. Rainwater, slightly acidic due to dissolved carbon dioxide, can dissolve these minerals and break down the rock.
* Oxidation: Minerals in rocks react with oxygen, forming oxides that are weaker and more easily broken down. This is why iron-rich rocks often turn reddish-brown.
* Hydrolysis: Water reacts with minerals in rocks, breaking them down into new minerals that are often weaker and more easily eroded.
* Biological Weathering: Living organisms, like lichens and bacteria, produce acids that can break down rock, and their roots can also contribute to mechanical weathering.
3. Biological Weathering:
* Burrowing Animals: Animals like moles, rabbits, and prairie dogs can dig tunnels, exposing new rock surfaces to weathering.
* Plant Roots: Plant roots can grow into cracks in the rock, exerting pressure as they expand and ultimately breaking the rock apart.
* Lichens: Lichens produce acids that can dissolve rock, breaking it down into smaller particles.
* Bacteria: Some bacteria can break down rock minerals and contribute to the weathering process.
Key Point: These processes often work together, with mechanical weathering creating cracks that chemical weathering can then exploit.
End Result:
Over time, these processes break down mountain rock into smaller fragments, which are then transported away by erosion. This process is essential for creating the soil that supports life on Earth.
