Weathering, erosion and sedimentation

Two processes, not one

Weathering is the wearing down or breaking of rocks while they are in place.^[1]

Erosion involves the movement of the fragments, and therefore differs from weathering, which concerns only decay in situ.^[1]

How rock is broken

Weathering is biological, chemical or physical. Burrowing animals and growing roots widen cracks. Carbon dioxide dissolved in rainwater makes it slightly acidic, and it reacts with minerals in the rock. Temperature change, wind, rain and waves break rock apart — most effectively where water freezing in a crack expands and forces it open.^[1]

How the pieces move

Six main processes do the moving, often together: gravity, wind, rain, rivers, oceans and glaciers. Material loosened by weathering travels from higher ground to lower, where another process may pick it up again.^[1]

Transport sorts as it carries. Flowing water drops the largest particles first and progressively finer ones as it loses energy — which is why grain size in a sedimentary rock is a record of the energy that delivered it.^[1,2]

And where it stops

Deposition is the laying down of that sediment by wind, water, sea or ice; dissolved material takes a different route, deposited later by organic activity or by evaporation.^[1]

Buried, compacted and cemented, the sediment becomes rock, and the sedimentary limb of the rock cycle closes.^[1,2]

The link upward

These processes are coupled to the tectonic engine. Mountain building raises rock into the reach of the atmosphere, and weathering and erosion begin removing it — an inference Lithoen labels as one, since neither cited source states the coupling directly.^[1,2]

Commonly misunderstood