Different rocks have different uses and different landscapes

1. Different rocks have different uses and different landscapes They do?

2. Remember there are 3 sources of rock Sedimentary? • Rock that was once magma • Rock that has been heated and/or squashed so much that the chemicals have been change to make totally new substances • Rock that has resulted from pieces being removed from other rocks by weathering or erosion, transported and then laid down and gently cemented together Igneous? Metamorphic?

3. Different rocks have different uses and different landscapes • Granite • Chalk • Limestone

4. Granite • What is granite like? • Granite is made up of three minerals: quartz, feldspar and mica. • It is a hard, crystalline rock, which is very resistant to erosion. • It is an intrusive igneous rock. This means it cooled slowly deep underground. • Over time the layers above it have been eroded away, leaving a high, often rounded area. • The main processes that affect it are freeze-thaw and chemical weathering.

5. The map on the left shows where you can see it However as you see from the detail of SW England – there is a whole lot more buried beneath the ground. Where might you find it?

6. These are Tors on Dartmoor • The main granite landforms are tors, which can be found on moors such as Dartmoor and Bodmin Moor. • Tors are blocks of granite that have weathered slower than the granite around them, because they have less joints and faults.

7. How the Tors formed • The granite seen on Dartmoor originated as a granite batholith, under the surface of the earth. A batholith is an area of molten rock that has cooled very slowly within the crust, creating a rock with large crystals. • Over time the material above the batholith was weathered and removed by rivers and glaciers. As this material was removed there was a reduction of pressure on the granite as there was less above it. This caused it to crack creating joints and cracks. • Where the joints were close together the most rapid weathering occurred, and quickly broke down the rock. However there were also areas where there were very few joints and so slower weathering occurred. The main form of weathering is freeze-thaw. • As this process continued over millions of years, the overlying material was totally removed, leaving behind the tors and valleys seen on Dartmoor.

8. Other landforms are … • Deep, steep v-shaped valleys, created as the water eroded through the cracks in the rock. • Marshes and bogs form due to the underlying impermeable granite preventing water from seeping away, and the high rainfall ( because the ground is often high) that many of these areas encounter. • Domes can occur in warmer climates created by onion skin weathering, producing spectacular scenery, as seen in Yosemite National Park. El Capitan

9. Uses of a granite area • Granite areas themselves have limited economic uses. • The soil is usually poor and thin, so little farming takes place, probably just some sheep and cattle grazing. • Because granite is impermeable, and the soil is poor, areas such as Dartmoor are ideal sites for reservoirs. • Quarrying occurs of granite itself, which is used in building (an excellent example being the city of Aberdeen, which is known as "the Granite City"). Granite is also used for things such as hearths, fireplaces, and gravestones. • Tourism is increasingly becoming important in granite areas. Many tourists just come to take in the fresh air and beautiful scenery, but the towns and villages of these areas are trying to cash in by opening guesthouses, cafes and other tourist facilities.

10. Limestone • What is limestone like? • Formed from the remains of organic matter, usually seashells and plants. It was formed under the sea 220-280 million years ago. • It is a hard, grey sedimentary rock, with a large number of joints (vertical cracks) and bedding planes (horizontal cracks) • Carboniferous limestone is an example of a pervious rock, as it allows water to flow through the joints and bedding planes. • The main processes which affect it is chemical weathering. Rainwater which is a weak acid dissolves the limestone • Two best areas of limestone in Britain are the Yorkshire Dales and the Peak District.

11. Carboniferous limestone produces distinctive karst scenery. These areas are dry on the surface due to the permeability of the rock, but have mainly been shaped by the action of water. Where you find limestone (yellow) and what it is like underground

12. Where you find limestone and what it is like underground • The water attacks the many joints and bedding planes in the rock, through the chemical weathering processes. • There are a number of distinctive features seen in karst scenery areas, both on and beneath the surface. • Limestone pavements are large areas of exposed limestone. When the overlying rock was eroded the pressure release on the limestone below caused it to crack even more. Hence limestone pavements are characterised by large gaps between the rock, called grikes. The remaining blocks of rock are called klints. • Limestone cliffs or scars are produced at the edge of the area of limestone. Often near vertical and highly jointed.

13. Swallow holes and sink holes are where rivers flow down into the rock. Sink holes are relatively small, whilst swallow holes are larger. Both have been formed either by the constant chemical attack of the water on the joints in the limestone, or by the collapse of a cavern below. Caverns are underground caves that have been hollowed out by the action of underground streams and by carbonation and solution. They have three distinctive features. Stalactites hang TIGHT from the roof of the cavern. Stalagmites grow MIGHTILY from the floor. Both are also lime deposits. Where a stalactite and stalagmite have joined you get a pillar. Where you find limestone and what it is like underground Also Stalactites hold onto the ceiling. Stalagmites are stuck to the ground

14. Underground streams flow down through the limestone carving out caverns, until the y reach the impermeable layer of rock below the limestone layer. Once at this point the stream flows under the limestone until it re-emerges. This is called resurgence. Gorges are created where the roof of a large underground cavern falls in, to create a steep sided gorge with a river running in the bottom. Where you find limestone and what it is like underground

15. What it looks like Resurgent Stream Stalagmites and stalactites Limestone Pavement Cheddar Gorge Sink hole

16. Uses of a limestone area • Poor, thin soils mean that the only type of farming possible in limestone areas is sheep grazing. • The tourist industry is a very important source of income to limestone areas. Most people come to walk in the hills and see the spectacular karst scenery. The local people are cashing in on this by opening café, guest houses and other tourist facilities. • Limestone is an excellent building stone, and has been used in some very well known buildings, such as the Houses of Parliament. Obviously this mean that there are often a large number of quarries. • Limestone, whether crushed or used as lime, can be very useful in a number of areas. It is used as an industrial cleanser, farmers use it as fertiliser and it forms an important ingredient in cement making.

17. Chalk and clay – they exist together • Chalk: • Formed 70 to 100 million years ago. It is a soft, white rock. It formed from the shells animals who lived in shallow warm seas. • Chalk is an example of a porous rock, as it has pore spaces, which can store water. It does not have joints and bedding planes like limestone. • Clay: • Is a product of chemical weathering and river erosion. • Clay is porous, but becomes impermeable when wet, as the particles expand and fill the pore spaces. • The main areas of chalk and clay in this country are in the South and East of the country. Places like the North and South Downs are good examples.

18. Chalk and clay landforms • Bournes are streams that occasionally flow down the dry valleys in times of prolonged wet weather, when the ground may have become saturated. • Clay vales are the valleys between the chalk escarpments. The clay, when drained is a fertile soil suitable for a range of farming methods. Clay vales are flat, and have a number of streams meandering through them. • Dry valleys, such as Devil's Dyke, were formed in periglacial times, when the ground froze, so melt water rivers ran over the surface of the chalk rather than flowing down through it. These rivers carved out steep sided valleys. Once the climate had warmed again a dry valley was left behind.

19. Chalk and clay landforms • Escarpments or cuesta's are the main landform of chalk and clay areas. Initially the layers of chalk and clay were tilted by the collision of the African and Eurasion plates. The soft clay was then eroded faster than the more resistant chalk, leaving escarpments (chalk hills) behind. Because of the angle of the tilt, these escarpments have two distinctive sides. The steeper side is called the scarp slope, whilst the gently sloping side is called the dip slope. • Springs form at the bottom of the escarpment, where the chalk meets the clay. This is why many settlements can be found along spring lines in chalk and clay areas.

20. A section through the North Downs Where are these?

21. Chalk and clay – uses of the landscape • Clay is very fertile, but must be drained first. Once that has been done farming includes dairying, sheep grazing, and some arable farming. On the chalk escarpments the main agriculture is sheep grazing. • Many settlements were built at the bottom of the scarp or dip slope, as the land was less likely to flood, there was a good water supply, and there was good farming land nearby. Very early settlements would have been higher up the chalk escarpment for defensive purposes. • Chalk is a main ingredient in cement making, and is quarried for that purpose. Clay can be used in pottery. • Underground aquifers act as a store for water within the chalk and are used as a natural water supply for London. • The gently rolling chalk hills with not much growing apart from grass make them a tourist attraction – rare plants and insects mean that many are SSIs (sites of special scientific interest) and this brings walkers.

22. Now to start on the homework • Open your homework and you will see a series of links. • These take you to different places where different kinds of rock are found. • Identify the picture(s) that go with the links and answer the questions.