Rocks, Resources and Scenery

All formed when molten rock (magma) from the mantle cools down and hardens. There are two types depending on where the magma has cooled down:

Intrusive eg. Granite

• Form when magma cools down below the Earth's surface.
• It cools very slowly forming large crystals that give the rocka a coarse texture.
• Large domes of cooled magma form domes of igneous rock called batholiths.
• Where the magma has flowed into gaps in the surrounding rock it forms dykes (in vertical gaps) and sills (in horizontal gaps).

Extrusive eg. Basalt

• Form when lava cools down after it's erupted from a volcano onto the earths surface.
• It cools down very quickly formiing small crystals that give the rocks a fine texture.

Formed when layers of sediment are compacted together until they become solid rock. The process of compaction is called lithification.

• Carboniferous limestone and chalk are formed from calcium carbonate. Layers of tiny shells and skeletons of dead sea creatures are deposited on the sea bed and compacted together over time.
• Clays and shales are made from mud and clay minerals. The particles have been eroded from older rocks, deposited in layers on lake or sea beds then compacted together.

* Sedimentary rocks often contain fossils.

Formed when other rocks (igneous, sedimentary or older metamorphic rocks) are changed by heat and pressure.

• Rocks deep in the Earth are changed by the pressure from the weight of the material above them.
• When tectonic plates collide, rocks are changed by the massive heat and pressure that builds up.
• Magma from the mantle heats the rocks in the crust causing them to change.

The new rocks are harder and more compact eg. Limestone becomes Marble. Clay becomes Slate.

Freeze thaw

• When it rains water gets into the cracks in the rocks
• At night the water freezes and expands, which puts pressure on the rock
• The water thaws the next day, releasing the pressure, then re freezes the next night
• Repeated freezing and thawing widens the cracks and causes the rock to break up

Exfoliation

• Each day the surface layers of rock heat up and expand faster than the inner layers
• At night the surface layers cool down and contract faster than the inner layers
• This creates pressure within the rock and causes thin surfaces to peel off

Solution weathering

• Some minerals that make up rock dissolve in water
• The minerals dissolve in rainwater, breaking the rock down

Carbonation weathering

• Rainwater has carbon dioxide dissolved in it, which makes it a weak carbonic acid
• Carbonic acid reacts with rocks that contain calcium carbonate, eg Carboniferous limestone, so the rocks are dissolved by the rainwater

• Plant roots break down rocks by growing into cracks on their surfaces and pushing them apart
• Burrowing animals may loosen small amounts of rock material

Tors

• Granite has lots of joints which aren't evenly spread ( they're closer together in some parts )
• Freeze-thaw and chemical weathering wear down the parts of the rock with lots of joints faster because there are more cracks for the water to get into.
• Sections of granite hat have fewer joints are weathered more slowly than the surrounding rock and stick out at the surface forming tors

Granite is also impermeable - it doesn't let water through
This creates moorlands - large areas of waterlogged and acidic soil, with low growing vegetation

Escarpments

• Horizontal layers of chalk and clay are sometimes tilted diagonally by earth movements
• The clay is less resistant than the chalk so is eroded faster
• The chalk is left sticking out forming escarpments/cuestas ( hills ). Where they clay has been eroded it forms vales - wide areas of flat land
• Escarpments have steep slopes ( scarp slope ) on one end and gentle slopes (dip slope ) on the other

Chalk is an aquifer - a permeable rock that stores water

Water flows throughout the chalk and emerges where the chalk meets impermeable rock
Where the water emerges is called a spring line

Areas of chalk can also have dry valleys - valleys that don't have a river or stream flowing in the, because the water is flowing underground

• Limestone pavements are flat areas of limestone with blocks separated by weathered-down joints
• Swallow holes are weathered holes in the surface
• Caverns form beneath swallow holes where the limestone has been deeply weathered
• Limestone gorges are steep sided gorges formed when caverns collapse
• Limestone is permeable so limestone areas also have dry valleys and resurgent rivers ( rivers that pop out at the surface when limestone is on top of impermeable rock )
• Water seeping through limestone contains dissolved minerals. When the water drips into a cavern the minerals solidify and build up over time to produce stalactites ( on the ceiling ) and stalagmites ( on the ground )
• When stalagmites and stalactites meet in the middle they form a pillar. When water flows in as a sheet a curtain builds up