Physical Geography - Rocks and Weathering

• Inner core - Solid ball of iron and nickel. It is very hot due to high pressure and radioactive decay (contains uranium which gives off heat when decompose). Responsible for earth's internal energy.
• Outer core - Semi-molten and is made up of iron and nickel.
• Plate tectonic theory - The earth's crust and lithosphere is made up of large slabs of rock which called tectonic plates (oceanic and continental) which move around due to convection currents in the mantle below which drag and pull the plates.
• Convection currents are caused when the less dense magma rises, cools then sinks
• Plate boundaries/margin - The edge of two plate tectonics and where they meet and interact with each other, potentially subducting or pulling apart.
• Divergent boundary - Two plates moving away from eachother. This can be seen at mid ocean ridges as new material forms between them.
• slab pull When an oceanic plate subducts the continental plate into the mantle it pulls the rest of the plate (slab) with it causing further subduction. Or the process of the lithosphere pulling away from the asthenosphere.
• Ridge Push - The slope created when plates are moving apart a constructive plate boundary has gravity acting upon it as it has a higher elevation. Gravity pushes the plates further away, widening the gap (as this movement is influenced by gravity it is also known as gravitational sliding)
• Sea Floor Spreading -

  The formation of new, fresh oceanic crust and land due to the rising of magma at mid ocean ridges and the outward movement either side.
• Oceanic-oceanic constructive plate margin-

  Plates are moving away from each other due to convection currents in the mantle/asthenosphere below which causes magma to rise to fill the gap and then cool to form new land. Less explosive underwater volcanoes are formed. New land forming on the ocean floor by lava filling the gaps is known as sea-floor spreading.
• Mass movement - The large scale movement of material down a slope due to gravity when the shear stress exceeds the shear strength, causing instability
• Mass movement on a slope will always been downwards due to gravity. These movements can happen over a range of timescales, and also depend on the moisture in the hillslope material.
• Mass movement processes also depend on the material the slope is made from. Different structures have different internal strengths.
• Types of slope material

  Non-cohesive materials such as coarse grains like sand

  Cohesive materials such as silts and clays

  Rock such as sandstone and slate.
• There are 4 types of mass movement

  • Heaves
  • Flows
  • Slides
  • Falls
• How are heaves formed?

  They occur on slopes made from cohesive and non-cohesive materials.

  Frost heave and soil creep are two different types of heaves

  Heaves are the slowest and most prevalent form of mass movement.
• Shear Strength - Shear strength is defined as a material's ability to withstand forces which cause the material's internal structure to slide against itself. The maximum shear stress that soil or materials can withstand without sliding or experiencing failure.
• Sher strength - Shear stress is a measure of the intensity of the forces causing deformation or slippage along a specific plane within a material.
• How are heaves formed?

  Heaves occur when soil particles are pushed, and then due to the influence of gravity- the particles move downwards. On slopes made from cohesive materials, this can cause the soil to ripple, creating steps called terracettes.
• Formation of divergent plate boundary (Oceanic and Oceanic)

  The two plates are moving apart from one another due to convection currents in the asthenosphere below and also due to ridge push. Magma rises to fill the gap and cools and solidifies to form a mid-ocean ridge which is separated by a rift valley. It forms new oceanic crust due to sea-floor spreading which is the process by which magma rises and cools to form new crust
• Ridge push - The intrusion of magma into the mid-Atlantic ridge at a divergent plate boundary which propels plates apart due to gravity.
• Slab pull - Process by which subduction of an oceanic crust beneath the continental crusts leads to the further subduction of the entire plate because of gravity
• Convergent plate boundary (Oceanic Continental):
• Two plates are moving towards each other due to convection currents in the asthenosphere
• Oceanic crust is forced underneath the continental crusts because it is denser (3.0g/cm^2 compared to 2.6g/cm^2)
• An ocean trench is formed due to subduction
• Material from the ocean and trench is scrapped off to form an accretionary prism
• Oceanic crust is partially melted in the Benioff zone
• Magma rises to form composite volcanoes
• Fold mountains are formed when compression due to plate collision squeezes rock material into layers
• Forced rock layers rise upwards, known as orogenesis