Geography- Rocks

These are about the topic rocks in AQA Geography A

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  • Created by: Sam
  • Created on: 07-06-12 15:04

Generally about Rocks

The geological timescale is the 542 million years since life was abundant on earth spilt up into eras and periods. An era is made up of periods.

Rock Types

Igneous- Formed by the cooling of molten magma either instrusive (formed underground) or extrusive (formed through volcanic activity). E.g Granite

Sedimentary- Formed ny compaction of sediments usually deposited at sea. Can be organic or inorganic. E.g Chalk, Clay, Limestone

Metamorphic-Formed by alteration of pre-existing rocks by heat and/or pressure. E.g slate formed by pressure from clay.

The rock cycle shows the connection between the rocks

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Weathering

Weathering is the breaking down or disintergration of rocks in their original place

Types of Weathering

Mechanical- also known as physical invloves the break-up of rocks without any chemical changes. Often results in scree. E.g freeze-thaw and exfoliation

Chemical- chemical changes occur. Rainwater is slightly acidic can slowly dissolve rocks and minerals. E.g Solution and Carbonation (when carbonic acid in rainwater reacts with calcium carbonate to form calcium biocarbonate)

Biological- involves actions of plants and animals. E.g. plant roots expand cracks in rocks and some animals like rabbits burrow into weak rocks

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Granite Landscapes

Granite is a tough intrusive igneous rock resistant to weathering so it forms upland areas. Some minerals are vunerable to chemical weathering and the result is china clay.

Granite consists of cracks and joints formed when the granite cooled or when pressure was released. These cracks make granite vunerable to freeze-thaw weathering. Despite the joints granite is still impermeable so it has many surface water features like rivers and lakes.

The most destinctive granite landform is the tor. An outcrop of rock above the ground. They are formed because the number of vertical joints varies making some areas more vunerable to weathering than others. Zones of closely spaced joints are weathered rapidly compared to zones of widespread joints. As the granite becomes exposed the zones of widespread joints stand above the rest forming tors.

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Chalk and Clay

Both are sedimentary rocks formed under the sea uplifted by tectonic activity.

Most chalk is found in the south and east of England in bands because it is sedimentary it was formed it layers then uplifted that way. It is physically tough and forms upland areas (it is permeable/porous and lack of rivers = lack of erosion). Water can be stored within the chalk up to the water table.

Chalk and Clay together form Scarp and Vale Landscapes. Clay erodes much quicker than Chalk. This leaves the chalk standing above the Clay in escarpments. The steep slope is the scarp slope and the gentle one the dip slope. Springs form between the Chalk and Clay where the water table emerges. (these features form because the rock has been exposed at an angle due to tectonic activity)

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Limestone

Sedimentary rock formed in tropical seas in the Carboniferous period. It also forms in bands like chalk. It is also a tough resistant rock that forms upland areas such as the Pennine Hills and Mendips but it is very vunerable to chemical weathering.

Limestone has many underground features such as caves, gorges, stalagmites, stalactites, pillars and curtains. These are formed as water flows through the limestone eroding or dissolving (then depositing) it.

It also has many surface features such as limestone pavements with clints (the slab) and grikes (the gaps), swallow holes where water flowing over impermeable rock dissapears down holes in limestone and ressurgences where water flowing underground emerges onto the ground surface.

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Issues with Quarrying

Quarrying destroys habitats and damages the environment, transport and machinary increases use of greenhouse gases and the visual impact is terrible (after all it is just a big hole in the ground).

There are now strict environmental controls on quarrying both during production and after the Quarry has been exhasted. Companies are expected to restore the quarry at least to the original environmental qualities of the area.

There are many uses for exhasted quarries such as farmland, courses for motocross or biking, many contain lakes that can be used as wildlife reserves or they can be used as landfill sites.

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Comments

Husna

Geography certainly doesn't rock!

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