weathering Flashcards
weathering
the breakdown of rocks by physical, chemical or biological processes - it takes place on site, so there is no movement involved
physical weathering
breaking down of rocks, mineral, and soils without chemical change
process of freeze-thaw weathering (model answer)
During the winter in the British Isles temperatures are below 0 °C on many nights but above 0 °C during the days.
Water gets trapped in the cracks in the rock. It expands when it freezes at night, pressurising the sides of the rock.
During the day the ice melts and contracts, releasing the pressure on the rock cracks.
Alternating expansion and contraction weakens the rock and pieces break off.
This is called FROST SHATTERING.
If this process happens to rocks at the top of a steep slope it produces scree (piles of rocks) at the foot of the slope
process of onion-skin weathering in hot deset climates (model answer)
Hot desert areas have a big daily temperature range (35 °C in the day, 10 °C at night).
Each day, surface layers of rock heat up and expand. At night the cold makes them contract - this causes thin layers to peel off.
biological weathering
the breaking down of rocks by organisms
how can plant roots be a cause of biological weathering
Plants can grow down through cracks in rock surfaces and push them apart, loosening fragments
how can burrowing creatures be a cause of biological weathering
Burrowing creatures, e.g. rabbits and worms, break up softer rocks like clay
how can decay be a cause of biological weathering
Decaying plants and animal remains make acids which eat away at the rocks below.
chemical weathering
the weakening and disintegration of rock by chemical reactions
explain how limestone areas are weathered when limestone reacts with rainwater (a weak acid) (model answer)
When it rains the limestone rock is dissolved along weaknesses called joints (vertical weaknesses in the rock) and bedding planes (horizontal weaknesses)
This process forms special features called solution features.
examples of solution features
1) Caves
2) Swallow holes - where a river disappears down into the limestone
3) Clints (blocks of limestone) and grikes (the gaps between the blocks) - which make up a limestone pavement
4)Stalactites and stalagmites - water droplets evaporate, leaving traces of limestone which grow on cave roofs and floors.
example of a limestone area with lots of solution features
Malham in North Yorkshire
