Rocks + Weathering

• Inner core


  Solid ball of iron/nickel, very hot due to pressure and radioactive decay
• Outer core


  Semi-molten iron/nickel
• Mantle


  Mainly solid rock high in silicon, top layer is semi-molten magma (asthenosphere)
• Asthenosphere


  Semi-molten layer that constantly moves due to convection currents powered by heat from the core
• Lithosphere


  Broken up into plates, majority is within the mantle, top is the crust
• Crust


  The thin top of the lithosphere, oceanic crust is dense and destroyed by plate movement, continental crust is less dense and not destroyed
• Plate tectonic theory


  Lithosphere is broken into large slabs of rock called tectonic plates, plates move due to convection currents in the asthenosphere
• Plate boundaries


  • Edges where plates meet, can be destructive/convergent, constructive/divergent, or conservative
• Destructive/convergent plate boundaries


  • Continental and oceanic: oceanic plate subducts below continental, fold mountains, volcanoes
  • Oceanic and oceanic: heavier plate subducts, fold mountains, underwater volcanoes, island arcs
  • Continental and continental: pressure builds, fold mountains
• Constructive/divergent plate boundaries


  • Oceanic and oceanic: magma rises in gap, new land forms, less explosive underwater volcanoes, sea floor spreading
  • Continental to continental: rift valley forms, volcanoes
• Ridge push


  Gravity pushes plates further apart as they move
• Slab pull


  Subducting plate pulls the rest of the plate with it, causing further subduction
• Conservative plate boundary


  • Parallel plates move in different directions or speeds, no plates destroyed so no landforms created, can cause fault lines
• Hotspots


  Areas of volcanic activity not related to plate boundaries, hot magma plumes rise and burn through crust, can create volcanoes and islands
• Physical weathering


  Weathering that affects rocks and rock formations
• Freeze-thaw


  • Water freezes in cracks, expands, and causes rocks to shatter and break off
• Heating/cooling processes


  • Repeated heating and cooling causes rocks to expand and contract, leading to layers peeling off (exfoliation)
• Salt weathering


  • Salt crystals form in cracks and pores, build up pressure and cause rocks to break apart
• Pressure release (dilatation)


  Rocks under great pressure expand and fracture when the pressure is removed (e.g. through erosion)
• Vegetation root action


  • Growing roots exert pressure on surrounding rocks, causing them to break apart
• Chemical weathering


  Breaking down of rocks caused by chemical reactions
• Hydrolysis


  Rocks break down when they react with water
• Hydration


  Water is absorbed into a substance, causing a new substance to form
• r tremendous
• pressure , and when the load above is eroded away , the pressure is removed , and the rock
• Vegetation Root Action


  When vegetation grows , such as plants and trees, their roots also grow and thus need more space
• The growing roots


  Exert pressure onto the surrounding rock, eventually causing the rocks to break apart
• Chemical Weathering


  The breaking down of rocks caused by chemical reactions
• Hydrolysis


  Weathering is the breaking down of rock when it reacts with water (hydro-)
• Rocks can break down when they are soluble in water , for example chalk can react and break down in water.
• Hydration


  Occurs when water is absorbed into a substance, causing a new substance to form
• Hydration

  Causes rocks to expand in size and volume , which can make them susceptible to other forms of weathering
• Carbonation


  When CO2 dissolved in water (known as carbonic acid) reacts with rocks and breaks them down
• CO2 can dissolve into rainwater due to emissions of CO2 into the atmosphere, or dissolve into groundwater and create caves/sinkholes making this a widespread issue
• Factors Affecting Weathering


  • They affect the rate, type, and severity of weathering
• Climate


  Temperature and precipitation play an important role in weathering
• In alpine climates where temperatures fluctuate more rapidly than in polar environments


  Freeze-thaw weathering is more severe
• In dry climates


  Salt crystal growth favours, allowing the water to evaporate to leave the salt crystals
• Rock type and structure


  Dictates the rate at which weathering will occur, and also what type of weathering (be it physical or chemical, or both) will take place
• Some rocks, e.g. water soluble rock types, are more vulnerable to chemical erosion, and therefore will be weathered at a quicker rate