Rocks, granite, limestone and chalk


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Rocks, granite, limestone and chalk

  1. 1. ROCKS AND LANDSCAPES Case study revision material.
  2. 2. Granite- Dartmoor <ul><li>The upland is granite , one of the toughest rocks. </li></ul><ul><li>Magma which formed the Dartmoor granite cooled and solidified slowly within the earth’s crust. </li></ul><ul><li>Millions of years of weathering and erosion stripped away the overlying rocks, exposing granite at the surface. </li></ul>
  3. 3. Granite - Dartmoor
  4. 4. Granite- Dartmoor <ul><li>The appearance of granite landscapes is due to the rock’s hardness , impermeability and many joints . </li></ul><ul><li>The typical granite landscape is </li></ul><ul><li>Rugged uplands </li></ul><ul><li>Poorly drained- with areas of boggy moorland </li></ul><ul><li>Dominated by isolated rock outcrops called tors, formed by deep chemical weathering along the granite’s vertical joints. </li></ul>
  5. 5. Granite- Dartmoor <ul><li>The most striking features are masses of weathered granite such as Hay Tor and Bowerman’s nose, rising 20+m above the ground. </li></ul>
  6. 6. Granite- Dartmoor- land use <ul><li>Upland areas with steep slopes and poor soils </li></ul><ul><li>Rough grazing for sheep </li></ul><ul><li>Recreation (walking/climbing) </li></ul><ul><li>Tourism </li></ul><ul><li>Quarrying for granite to use as kerb stones, building materials such as facing stones, china clay etc. </li></ul><ul><li>Princetown jail- isolated, remote- an ideal location for prisoners. </li></ul>
  7. 7. Limestone- Malham, Yorkshire Dales <ul><li>The largest area of limestone in the UK is in the Y. Dales </li></ul><ul><li>The distinctive property of hard Carboniferous limestone is that is dissolves slowly in rainwater </li></ul><ul><li>Rain falls through the atmosphere absorbing carbon dioxide gas to form a weak carbonic acid which soaks into the limestone. </li></ul>
  8. 8. Limestone- Malham, Yorkshire Dales <ul><li>Limestone is pervious - meaning water sinks down the joints and along the bedding planes. </li></ul><ul><li>The carbonic acid reacts with the limestone to form calcium bicarbonate, which dissolves in water. </li></ul><ul><li>A limestone surface is lowered at around 4cm per 1000 years. </li></ul>
  9. 9. Limestone- Malham, Yorkshire Dales <ul><li>The carbonation (chemical weathering) results in a distinctive limestone or karst scenery. </li></ul><ul><li>The main features of karst scenery are limestone pavements, scars, shake holes, swallow holes, sink holes, caves, caverns, stalactites, stalagmites. </li></ul>
  10. 10. Limestone pavements <ul><li>These are bare surfaces of limestone. Solution of limestone by acidic rainwater enlarges the joints to form deep, narrow grykes . The rectangular blocks between the grykes are known as clints . </li></ul>
  11. 11. Dry valleys and gorges <ul><li>These were cut by rivers and streams that used to flow on the surface but have since disappeared underground. They may have formed when the water table was at the surface or when the ground was frozen during colder climatic conditions. </li></ul>
  12. 12. Swallow holes <ul><li>Streams flowing across impermeable rock disappear underground when they meet the pervious limestone. The enlarged vertical joint down which the stream plunges becomes a swallow hole. </li></ul>
  13. 13. Caves and caverns <ul><li>The solution along joints and bedding planes leads to the formation of caves and underground features . Dissolved limestone may be deposited in the form of finger like stalactites which hang from the roofs of caves. Stubby stalagmites are built up where the drips fall on the cave floor . Pillars form when stalactites and stalagmites join together. </li></ul>
  14. 14. Resurgence <ul><li>Underground streams reappear at the surface where the limestone meets the underlying permeable rock. This is known as a resurgence. </li></ul>
  15. 15. Chalk- The South Downs <ul><li>Chalk is a type of soft limestone </li></ul><ul><li>It is porous- it acts like a sponge trapping water in the tiny air spaces (pores) between it’s mineral particles </li></ul><ul><li>There are few permanent streams and rivers- as the rock is so porous </li></ul><ul><li>Settlements cluster around wet points such as springs. </li></ul>
  16. 16. Chalk- The South Downs <ul><li>Springs commonly occur in chalklands: </li></ul><ul><li>At the foot of steep scarp slopes where the chalk rests on impermeable rock such as clay </li></ul><ul><li>On dip slopes where the zone of saturated rock (water table) reaches the surface. </li></ul>
  17. 17. Chalk- The South Downs <ul><li>The South Downs are a line of chalk hills (an escarpment) averaging 200m in height. </li></ul><ul><li>In several places the escarpment is cut by the valleys of the southward flowing rivers such as the Ouse and Cuckmere </li></ul><ul><li>Although chalk is relatively soft chalk often forms bold features such as escarpments, because: </li></ul><ul><li>It is more resistant than the surrounding rocks which are worn down more quickly </li></ul><ul><li>There are few streams and rivers (normally the main factors in erosion) in chalk land areas. </li></ul>
  18. 18. Clay <ul><li>Clay is one of the least resistant rocks and is easily weathered and worn down by rivers and glaciers </li></ul><ul><li>Clay forms extensive flat lands called vales </li></ul><ul><li>Clay is impermeable </li></ul>