The Rock Cycle (Cambridge (CIE) IGCSE Environmental Management): Revision Note

Weathering & erosion

• The rock cycle is a continuous process that shows how rocks change from one type to another over time

• Weathering is the breakdown of rocks in-situ, at or near the Earth’s surface, into smaller pieces

  • Caused by physical, chemical, and biological processes

  • Physical weathering: caused by temperature changes, freeze-thaw action, and wind or water movement, breaking rock apart

  • Chemical weathering: caused by chemical reactions, such as acid rain dissolving minerals in rocks

  • Biological weathering: caused by plant roots or animals breaking down rock

• Erosion is the removal of weathered rock particles from their original location

  • Carried out by wind, rivers, glaciers, or waves

  • Over time, erosion wears away landforms and creates new ones, like valleys and cliffs

Transportation

• Transportation is the movement of eroded material from one place to another

  • Carried out by wind, rivers, glaciers, or waves

  • The material moved is called sediment—small pieces of rock and mineral

  • Larger, heavier particles are carried only short distances, while smaller, lighter ones travel further

  • When the moving water, wind, or ice loses energy, the material it is carrying is dropped

Deposition

• Deposition is the process of sediment being dropped or laid down after transport

  • It happens when the moving force loses energy and can no longer carry the material

  • Deposition is the first stage in the formation of sedimentary layers

  • Once sediment has been deposited, sedimentation begins as the layers build up over time

  • Deposition also creates features such as river deltas, sand dunes, and beaches

Sedimentation

• Sedimentation is the process by which transported materials settle out of moving water, ice, or wind

  • Starts after deposition, when sediments settle and begin to collect on top of each other

  • Sediments build up in layers at the bottom of rivers, lakes, and oceans

  • Larger, heavier sediments settle first, while lighter ones stay suspended longer

  • The weight of new layers adds pressure to the layers below, preparing them for compaction

  • Over long periods, these layers form sedimentary deposits that can later become rock

Compaction

• Compaction is when pressure from the layers of sediment above squeezes the lower layers together

  • Water and air are pushed out from between the grains

  • The sediment becomes denser and starts to form solid rock

Cementation

• Cementation happens when minerals crystallise and glue compacted particles together

  • Minerals such as silica or calcium carbonate fill the spaces between grains of rock

  • This binds the sediments to form sedimentary rock

Insert image: Compaction and cementation
Compaction and cementation

Crystallisation

• Crystallisation is the process by which molten rock cools and forms crystals

  • When magma or lava cools, minerals form solid crystals that make up igneous rocks

  • Slow cooling underground produces large crystals, as seen in granite

  • Rapid cooling on the surface produces small crystals, as seen in basalt