Alistair McNaught; Peter Symonds College 2001 The rock cycle describes the perpetual recycling of minerals by * weathering and erosion processes on the surface * transport and deposition processes involving water, ice, waves or wind * rock creation and transformation involving crustal and tectonic processes * Landscape creation Weathering and erosion Transport and deposition Rock creation Rock transformation Landscape creation Weathering & erosion Transport & deposition Rock creationRock transformation

Alistair McNaught; Peter Symonds College 2001 Landscape creation Weathering & erosion Transport & deposition Rock creationRock transformation Chemical weathering: Water penetrates rocks The presence of water results in solution weathering (soluble minerals dissolve) carbonation (CO2 enriched water dissolves limestone) hydrolysis (feldspars degrade to clays) hydration - salts swell on water uptake Physical weathering: Water in rocks freeze - expanding joints Extremes of heating cause thermal weathering Release of pressure as surface layers wear away Rocks Erosion is distinguished from weathering because erosion involves removal of material whereas weathering involves only rotting of material. Erosion therefore implies transport of weathered material

Alistair McNaught; Peter Symonds College 2001 Landscape creation Weathering & erosion Transport & deposition Rock creationRock transformation Transport takes place by: Ice - glaciers wear down highland areas Water - rivers and streams move material to the oceans from the land Wind - particularly in areas of low rainfall Deposition takes place in: the ocean inland lakes river floodplains inland basins (eg rift valleys) Deposition of eroded sediment sets the scene for the creation of new rocks (sedimentary rocks) from the rotted, weathered and eroded remains of the old rocks.

Alistair McNaught; Peter Symonds College 2001 Landscape creation Weathering & erosion Transport & deposition Rock creationRock transformation Ocean The first stage of rock creation is burial - sediment is buried by later layers of sediment being deposited. The pressure of overlying sediment squeezes the water out of the sediment - this is dewatering and compaction. Finally, cementation takes place as minerals dissolved in the in the sediments precipitate out and cement together adjacent grains of sediment. At this stage the rock is forming and lithification has taken place

Alistair McNaught; Peter Symonds College 2001 Landscape creation Weathering & erosion Transport & deposition Rock creationRock transformation Sedimentary rock Metamorphic rock Sedimentary rocks laid down in the ocean become increasingly buried by younger sediments. As they gradually subside into the crust they experience increasing heat and pressure. This changes the structure and composition of their minerals to create Metamorphic rocks. Pressure Heat Metamorphic rocks can also be created dynamically by crustal plate movements. Intense heating and pressure at plate collisions eventually melts the rock. Molten rock (magma) rises through the crust. Some solidifies underground to form intrusive igneous rocks. Others rise to the surface erupting as extrusive igneous rocks - for example, lavas. Intrusive igneous rocks Extrusive igneous rocks Regional metamorphism

Alistair McNaught; Peter Symonds College 2001 Landscape creation Weathering & erosion Transport & deposition Rock creationRock transformation Extrusive igneous rocks create distinct volcanic landscapes like those of central America. After many millions of years of erosion the underlying intrusive igneous rocks may be revealed, creating a distinctive granite landscape like Dartmoor in SW.England The plate collisions - resulting in large scale regional metamorphism underground - are expressed on the surface as large scale fold mountain ranges such as the Himalayas. As soon as new rocks are exposed on the surface by either uplift (fold mountains) or eruption (volcanoes), weathering and erosion start the whole cycle again. The Rock Cycle is powered by two energy sources - 1) geothermal heat (to drive plate tectonics) 2) solar energy (to drive climate and therefore weathering and erosion systems)

Alistair McNaught; Peter Symonds College 2001 Weathering and erosion Transport and deposition Rock creation Rock transformation Landscape creation