The Rock Cycle (Cambridge International IGCSE Environmental Management)

Weathering & erosion

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

The rock cycle

• 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

The process of freeze-thaw weathering

The process of biological weathering

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

Exam Hint Many students confuse deposition and sedimentation. Think of deposition as the moment the sediment drops out of moving water or wind, and sedimentation as what happens after—when those sediments build up in layers.

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

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