Form under the surface of the earth, cooling very slowly to form large batholith Exposed after millions of years of erosion Rock has low porosity and permeability but water easily pass through joints Joints are cracks formed during cooling and shrinking of the magma Cracks are further enlarged by pressure release Three main minerals: Quartz Feldspar Mica
Freeze thaw action occurring in joints of highland areas Feldspars in granite are easily weathered by hydrolysis Quartz is tough mineral which will not be weathered and will be left behind The minerals are made of different colours, – they are susceptible to insolation weathering and resulted in granular disintegration.
Theories of Tor formation:1. Initial formation of vertical joints in the granite2. Removal of overlying rock (2-3m thick) and creation of horizontal joints3. Sub-surface chemical weathering widening the joints ( Hydrolysis resulting in kaolinisation)4. Deep weathering of granite5. Frost shattering and exposure of granite by solifluction in periglacial times
Taught to have been formed by weathering deepunderground before granite became expose on thesurface1. Despite being very strong, granite is very vulnerable to chemical weathering, Feldspar readily reacts with acidic water to form kaolin and this hydrolysis process weaken the granite causing it to crumble apart2. Granite is heavily jointed and the density of jointing is believed to have been a critical factor
Formed from the remain of organic matter, usually seashells and plants Formed under the sea, over 200 millions ago Limestone rock has no pore spaces because the rock is so old. Layers of limestone become very compressed and cemented under the weight of overlying sediments Very strong and resistant to erosion Able to form steep slopes without collapsing
Has large numbers of joints and bedding planes These lines of weaknesses allow water to pass through the rock to produce Karst scenery Composed mainly of mineral calcium carbonate which is insoluble The main processes, which affect it are carbonation and solution
1. Surface features caused by solution: Limestone pavement- large area of bare exposed rock- When overlying rock was eroded, the pressure release on limestone below caused it to crack even more.- Characterise by large gaps between the rock called grikes.- The remaining blocks are called clints .
2. Drainage Features: Swallow holes and sink holes are where river flow down into the rock. Sink holes are relatively small while Swallow holes are larger Both have been formed by constant chemical attack of water on joints or by the collapse of a cavern below
3. Surface features resulting from underground drainage Poljes - in the tropics, the landscape may be composed of either cone shaped hills and polygonal depressions E.g. ‘cockpit country’ (Jamaica) Tall isolated towers rising from wide plains - (Guilin, China) Dry valleys – a river valley without a river. a common feature on chalk and limestone
4. Underground features and underground depositional features Cavern - underground caves that have been hallowed out by the action of underground streams and by carbonation and solution. Three distinctive features: Stalactites – hang from the roof of the cavern, and basically lime deposits Stalagmites – grow from the floor and also lime deposits Pillars – where stalactites and stalagmites have joined