Geography AQA GCSE Weathering rocks landscapes and scenery

this is weathering that is done by animals and plants for example a tree or plant to could begin to grow in  a crack in a rock and as a result the crack would be forced open and coul even break the rock in two

something like footpath erosion which is done by humans is a form of biological weathering burrowing animals can also break rocks down by getting them to scrape along on another 

SPECIAL CASE 

you can have a bio chemical weathering an example of this is a limpet on a rock - the limpet has its stomacg on the outside if it when i goes looking for food on rock and it has acid in its stomach in the same way that humans do and this will dissolve some types of roc for example limestone and chalk at the coast

this is when a rock is broken down due to a chemical reaction this only happens to a few rocks like chalk and limestone 

an example of this is the process of carbonation this is where the rain has abosorbed some of the carbon dioxide in the air and this has created a carbonic acid which will dissolve rocks when the rain falls 

There are 2 examples of this you have exfoliation and freeze thaw weathering this is where rain water will get into a crack in a rock and as the temperature gets colder at night it will freeze and the water will expand and cause pressure to build up thus widening the crack and when it gets warmer in the day the water will melt and this will reduce the pressure and the water will go further into the crack which has been widened - this can take a long time and is more likely to tae place in a place where the temperature varies a lot  from day to night like  a desert

the same goes for  ex foliation ( or onion skin weathering) think about this in terms of exfoliating your skin - this is the process of breaking layers off a rock and this is done because of heat changes when the rock heats up it expands and when it gets cold it will contracts and the top layers will be put under a lot of stress from this action and will simply chip off the rock so it looks like the rock has layers