VIEWS: 15 PAGES: 8 POSTED ON: 10/13/2012
HIGHER REVISION GEOGRAPHY Coasts and mass movement. Longshore drift in this area has been responsible for the formation of sand bars across the mouths of several streams such as those in squares 8244 and 8345. When sand spits appear on an O.S. map the direction of the longshore drift can be determined as it will be moving towards where the end of the spit is being formed. Here, however, the direction of the longshore drift cannot be determined from the map as the spits have formed sand bars right across the river mouths. These bars have trapped water which form lagoons at Slapton Ley and Lower Ley in 8243 and the lake at 818411. On this extract, the term ‘point’ (meaning headland) appears at Warren Point, 667421, ‘cliff’ at West Cliff, 692383 and ‘cove’, indicating where erosion has produced a small bay, such as Redrot Cove at 668394 and Soar Mill Cove at 697376. Large headlands at Burgh Island, 646438 and Bolt Tail, 667396 stand out, suggesting a much more resistant rock type than in the area that lies in between these headlands. Smaller headlands like Warren Point and Thurlestone Rock, 675414 enclose sandy bays like the one at 676416. Off the headland there are small islands; Mew Stone 725359 and Little Mew Stone, 727358. These will be former parts of the headland now worn down to be stacks or stumps. Burgh Island was separated from the mainland by erosion. Over time the sand shown building up between Burgh Island and the mainland may become permanent and form a tombolo linking the island to the mainland. Symbol evidence is also important and we see the symbols for cliffs at 688383 and steep slopes at 704368. ROCKFALL Rapid, free-fall of rock from a steep cliff face. GRAVITY Freeze-thaw action loosening the rock. Bare lack of vegetation. well-jointed rock is very vulnerable A scree slope of fallen rock is formed at the bottom of the cliff. LANDSLIP or SLUMPING RAPID movements of a mass of earth or rock sliding along a CONCAVE plane. Occur after periods of HEAVY RAIN, when the water saturates overlying rock, making it heavy and liable to slide. PERMEABLE overlying IMPERMEABLE UNDERCUTTING of a steep slope by river or sea erosion weakens the rock above, also making a slump likely. MUDFLOW Occurs on steep slopes over 10°. It's a rapid sudden movement Occurs after periods of heavy rain or RAPID SNOWMELT. Not enough VEGETATION to hold the soil in place, saturated soil flows over impermeable sub soil. SOIL CREEP Very slow movement, occuring on very gentle slopes Soil particles repeatedly expand and contract in wet and dry periods. When wet, soil particles increase in size and weight, and expand at right angles. When the soil dries out, it contracts vertically. As a result, the soil slowly moves downslope. Describe and explain the hydrograph.
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