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2011-04-05 12:37:14
Geography Lisophere Limestone

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  1. Explain the formation of a lime stone pavement?
    • A limestone pavement is a large, flat outcrop of bare limestone lying horizontally on hillslopes or summits
    • it is formed when soil was stripped by glacial erosion which exposes the bare limestone to chemical weathering
    • Carbonation and solution chemically erode the exposed limeston and deepen and widen the joints in the rock(grikes)
    • Grikes are further deepened by frost action and plant roots
    • The higher limestone blocks are called clints.
  2. Explain the formation of Stalactites, Stalagmites and pillars.
    • Found in cave systems where the underground water is rich in calcium carbonate(CaCO3)
    • CaCO3 rich water percolates downwards through joints in the limestone.
    • As it reaches the open cave, some water evaporates and the CaCO3 is redeposited as Calcite
    • Stalagmites are rounded mounds of calcite which build up on the floor of the cave as the water drips splash on the ground
    • Stalagtites are calcite 'icicles' hanging from the roof of a cave formed as water drips downwards.
    • Where Stalactites and Stalagmites meet a calcite pillar forms
  3. Explain the formation of a swallow hole
    • A swallow hole is a very large joint where a stream disappears into the underground drainage system (intermitted)
    • They are found at the boundry of impermiable rock -eg Shale and the permeable limestone
    • The river flows on the surface across the impermiable rock but when it reaches the limestone the water reacts with the CaCO3 and carbonation and solution enlarge the joint so much that the river flows into the limestone.
    • Often an underground waterfall forms at a swallow hole- eg Gaping Ghyll
    • The stream flows underground along the bedding planes and down joints until it meets impermeable rock is forces to reapear at the surface at a resurgance point
  4. Explain the formation of a gorge
    • A gorge is a valley in limestone with near vertical cliffs. it is sometimes ocupied by a river.
    • it is thought to be formed from a roof collapse of an underground cavern
    • most likely to happen during meltwater surges at the end of the ice age which would have enlarged the underground cavern and de-stabalised it
    • Meltwater exploited the weak line of a major joint causing collapse of the cavern roof
    • may also have been formed due to rapid downcutting by a former river when the water table was higher