Water ShapingRock & Land

D. Crowley, 2008

Water Shaping Rock & Land

To know how water can shape both rocks and the land

Wednesday, May 3, 2023

Rock Cycle Look at the rock cycle below – clues A, B, C & D each

represent part of the cycle: can you work out which…

New rock formation

Weathering

ErosionTransport

Deposition

Rock Cycle

A – Rock particles are moved to new places by flowing water, strong winds etc… Fallen parts of the cliff faces are moved along by the sea

B – Water enters crevices in the rock, and ice forms expanding the crevices causing pieces to break off. Acid rain reacts with rock, which becomes weaker. Heat/cold expansion and contraction causes heat stresses breaking the rock. Wind causes loose particles to blast against rocks, wearing them away

C – Loose surface particles are worn away by rain, wind, rivers and sea. Channels in the ground are cut out by torrents of rain water, wearing away rock formations

D – Layers of particles which have been deposited are crushed from the weight of layers above. Water is forces out of each layer, so that the layers cement together in a solid rock

E – Particles fall due to gravity forming sediment. In water the most dense particles fall to the bottom first, followed by the less dense particles. Layers of different sediments form

D

E B

CA

Rock CycleNew rock formation

Weathering

ErosionTransport

Deposition

D

E B

CA

Weathering Weathering is the wearing away of rocks – this can be via

a physical, chemical, or biological process

Erosion Erosion is the movement of the broken pieces away from

the site of weathering

• E.g. a basalt cliff may be weathered by freeze-thaw (physical weathering) causing pieces of the cliff to break away

• Erosion happens when these pieces of rock fall away down the cliff (away from where they originally were)

Rock weathered

Rock eroded

Transportation Rivers and streams can move pieces of rock – this is

transportation

Fast flowing rivers can transport large rocks, but slow moving rivers can only transport tiny pieces of rock

As the pieces of rock are carried along by the water, they bash against each other and the river bed, gradually wearing away become smaller and more rounded

Deposited Finally the transported rocks are deposited when the river

does not have enough energy to carry them

Which rocks are likely to be deposited first – very large or very small rocks? Watch the deposition demo…

Very large rocks need a huge amount of energy to carry them – as the river slows energy is lost causing the large rocks to be deposited first

Mississippi River The Mississippi River carries 550 million tonnes of sediment

each year, deposited into the Gulf of Mexico – this builds the coast outwards by ~90m per year!

Where would you expect the largest rocks to be deposited at (A, B or C)? Explain your answer

Largest rocks would be deposited at A (as this point where the river still just had enough energy to move them)

A

B

C