Definition: The breaking down of rock IN SITU.
- Freeze-thaw. When water in cracks freezes and expands, then thaws and contracts, putting pressure on the rock and eventually breaking it. Common in periglacial areas where the temperature is DIURNAL.
- Pressure release. Where rocks on the surface are removed by erosion, causing the ones underneath to expand and fracture.
- Carbonation. Acid rain and CO2 reacts with chalk and limestone and breaks it down chemicallly.
- Hydration. When certain rocks absorb water and expand, e.g. anhydrate is changed to gypsum.
- The growth of roots into the rock.
- Animals burrowing and digging at the rock.
Factors affecting weathering
- Climate. Areas with high precipitation and high temperatures experience more weathering as the extremes cause more weathering to take place.
- Geology. The resistance of rock and its chemical composition affect the rate and possible ways it can be broken down e.g. limestone is easily weathered by carbonation and sandstone is easily weathered biologically.
Definition: When material is carried by the river as its load.
Finer materials e.g. silt and clay float along the middle-surface of the river.
Larger particles e.g. sand and gravel bounce along the river bed.
The largest material is rolled along the river bed.
In chalk and limestone areas, the rock is dissolved into the water.
SEDIMENT YIELD = the amount of material carried away by waterr measured in tonnes/km/year.