“A” and Mum write:
Rocks are broken down by erosion and by physical, chemical or biological weathering.
Physical weathering can be due to freeze-thaw, which happens when water gets in cracks in rocks, then freezes and expands, putting pressure on the rock before it thaws and releases that pressure, eventually causing the rock to split.
Another form of physical weathering is onion-skin weathering. This happens when rocks experience alternating extremely hot, then extremely cold temperatures, such as in a desert, until layers of rock start to peel off.
Chemical weathering happens when rain, which is acidic, eats away or dissolves the rock. This can cause holes, gaps and even caves.
Today we visited a limestone pavement. The limestone has been shaped into blocks (called clints) which have gaps in between (called grikes):
Some of the clints have holes which go down into the rock:
Biological weathering happens due to animals, plants and decay. For example, rabbits might burrow underground, causing the rocks above to collapse. Lichen clinging to rocks secrete an acid which eats away at the surface of the rock. Plants put out roots which can work their way in between the gaps in rocks, eventually prising the rocks apart.
