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rocks and landscapes

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  • 1. ROCKS! THERE ARE 3 DIFFERENT GROUPS OF ROCK – IGNEOUS, SEDIMENTARY and METAMORPHIC EACH TYPE OF ROCK IS WEATHERED and ERODED TO PRODUCE DISTINCTIVE LANDSCAPES WEATHERING is the natural process of rocks being broken down at the Earth‛s surface it is divided into physical, biological and chemical processes it is caused by rain, changes in temperature, plants and animals EROSION wears rock away and removes the loose particles is caused by glaciers, rivers, wind and the sea *ROCK FEATURES* HARDNESS strength of rock – resistance to weathering and erosion FOLD buckled or bent layers caused by tectonic movements PERVIOUS rock that allows water to pass through joints and bedding planes JOINTS vertical cracks of rock BEDDING PLANES horizontal cracks between layers in sedimentary rock FAULT fractures running through rocks caused by tectonic movements POROUS rock that allows water to pass through pores PERMEABILITY ability of water to pass through rocks
  • 2. IGNEOUS ROCKS Rocks can be IGNEOUS, sedimentary or metamorphic, depending on how they were formed IGNEOUS ROCKS (THESE ARE ALL FORMED FROM MOLTEN ROCK – MAGMA) *TECHNICAL BIT* EXTRUSIVE Igneous rocks are formed when magma spills out onto the surface and cools there (e.g. volcanic rocks) They have a fine texture (e.g. Basalt) When magma cools very slowly, large hexagonal columns appear e.g. Giants Causeway, N. Ireland INTRUSIVE Igneous rocks are formed when magma cools very slowly before reaching the surface They have a coarse (rough) texture (e.g. Granite) This process can cause features like the ‘Tors‛ on Dartmoor
  • 3. SEDIMENTARY ROCKS Rocks can be igneous, SEDIMENTARY or metamorphic, depending on how they were formed SEDIMENTARY ROCKS (THESE ARE FORMED ON THE SEABED FROM PARTICLES OF OTHER ROCKS or the REMAINS OF PLANTS AND ANIMALS) *TECHNICAL BIT* COAL is formed from the remains of tropical plants (especially those which are carbon rich) CHALK is the formed from the shells of tiny sea creatures; it also contains flint (made of calcium carbonate) LIMESTONE is coral, shells and micro-skeletons of sea creatures SANDSTONE is made from tiny particles of sand eroded from past landscapes by wind and water CLAY is particles of silt carried out to sea by rivers
  • 4. METAMORPHIC ROCKS Rocks can be igneous, sedimentary or METAMORPHIC, depending on how they were formed METAMORPHIC ROCKS (THESE ARE FORMED BY HEAT OR PRESSURE) *TECHNICAL BIT* METAMORPHIC just means ‘changed from‛ They happen when IGNEOUS or SEDIMENTARY rocks become transformed during VOLCANIC ACTIVITY or EARTH MOVEMENTS The New Rocks are HARDER, MORE COMPACT and CRYSTALLINE e.g. SANDSTONE QUARTZITE becomes LIMESTONE MARBLE becomes GRANITE GNEISS becomes CLAYS SLATE becomes
  • 5. PHYSICAL WEATHERING WEATHERING is the breakdown of rocks by PHYSICAL, chemical or biological processes – no movement involved PHYSICAL WEATHERING (THIS BREAKS DOWN ROCK SURFACES) FREEZE-THAW ACTION in temperate climates (areas that are neither very hot nor very cold) *TECHNICAL BIT* 1. In GB night temps 0°C 2. Water gets trapped in rocks, as it freezes, it expands (upto 9%) putting pressure on the rock sides 3. The next day the ice has made the crack bigger, ice melts and contracts releasing pressure on rock cracks 4. Alternating EXPANSION and CONTRACTION weakens rock and pieces break off by FROST SHATTERING. Produces scree (large piles of small broken bits of rock) FREEZE-THAW weathering is most rapid in places with temperatures going above and below 0ºC ONION SKIN WEATHERING in hot desert climates *TECHNICAL BIT* 1. Hot desert areas have a large temp range (35°C in day, 10°C at night) 2. Each day surface layers of rock heat and EXPAND. At night the cold temps makes the rocks CONTRACT, causing thin layers to PEEL OFF
  • 6. BIOLOGICAL WEATHERING WEATHERING is the breakdown of rocks by physical, chemical or BIOLOGICAL processes – no movement involved BIOLOGICAL WEATHERING (THIS NEEDS PLANT ROOTS OR DECAY) *TECHNICAL BIT* Plant roots can grow down through cracks in the rock surfaces and push them apart, loosening fragments Decaying plants and animal remains make acids which eat away at the rocks below
  • 7. CHEMICAL WEATHERING WEATHERING is the breakdown of rocks by physical, CHEMICAL or biological processes – no movement involved CHEMICAL WEATHERING (THIS INVOLVES REACTIONS ON THE ROCK) *THE ‘EASY‛ TECHNICAL BIT* *THE ‘SLIGHTLY MORE DIFFICULT‛ TECHNICAL BIT* LIMESTONE AREAS are weathered when limestone reacts with rainwater (a weak carbonic acid) When it rains rock is DISSOLVED along weaknesses (like joints and bedding planes) forming solution features e.g. CAVES and SWALLOW HOLES Water droplets leave the dissolved rock behind on cave roofs and floors to form STALACTITES and STALAGMITES
  • 8. GRANITE LANDSCAPES The features and soils that make up a landscape depend on the type of ROCK and the type of WEATHERING DARTMOOR (THIS IS AN UPLAND GRANITE AREA IN SOUTH-WEST ENGLAND) *THE ‘EASY‛ TECHNICAL BIT* Granite is resistant to erosion and impermeable Dartmoor based on a Batholith Large Tors – joints enlarged by constant weathering Rivers have eroded steep sided V-shaped valleys Granite is impermeable – no water can soak through Marshes and bogs where water can‛t drain away
  • 9. CHALK LANDSCAPES The features and soils that make up a landscape depend on the type of ROCK and the type of WEATHERING SOUTH DOWNS (CHALKS AND CLAYS OCCUR TOGETHER FORMING GENTLY ROLLING HILLS CALLED DOWNS – SOUTHERN ENGLAND) *THE ‘EASY‛ TECHNICAL BIT* Chalk forms escarpments – with one gentle and one steep slope Chalk is porous so rainwater sinks in, leaving few surface streams but water reappears at bottom of escarpment as a spring Water stored in a chalk hillside can be used as a natural reservoir
  • 10. CARBONIFEROUS LIMESTONE LANDSCAPES The features and soils that make up a landscape depend on the type of ROCK and the type of WEATHERING YORKSHIRE DALES (THIS IS AN AREA OF STEEP SLOPES AND EXPOSED ROCKS IN NORTH-EAST ENGLAND) *THE ‘EASY‛ TECHNICAL BIT* Landscape produced by limestone called karst scenery Limestone produces flat-topped, moorlands with steep-sided gorges Water can‛t soak into limestone but it does enter it through cracks or joints leaving few surface streams Settlements at base of hills where water comes out (see also CHEMICAL WEATHERING)