geog

• Lithosphere:made of crust and uppermost mantle

  broken up into pieces called tectonic plates

  oceanic plate and continental plate
• lithosphere

  movement of tectonic plates will result in landforms and phenomena
• Asthenosphere

  lies below the lithosphere

  heat from the core causes the rocks in the asthenosphere to melt

  This drives movement of the tectonic plates
• Convection currents


  The movement of heat within the mantle
• Convection currents in the mantle

  1. Material in the mantle is heated by the core making it less dense

  2. Less dense material expands, rises and spreads out beneath the plates

  3. Plates are dragged along and move away from each other causing divergent plate movement

  4. Hot mantle material cools slightly and sinks back to the core, pulling the plate tectonics along

  5. Sinking mantle material heats up again as it nears the core and the whole process repeats

  6.The rising and sinking of the mantle material forms convection currents
• Slab pull force

  This happens when oceanic plate subducts under a less dense plate and pulls the rest of the plate along

  As the oceanic plate subducts, it is pulled by gravity downwards

  It sinks deeper into the mantle under its own weight, pulling the rest of the plate along with it

  The subducting plate drives the downward-moving portion of convection currents
• Sea floor spreading

  1.When two oceanic plates move away from each other sea floor spreading occurs

  2.Magma deep within the earth rises through the gap to form the mid-oceanic ridge

  3.This magma that rises up will be cooled down, the cool ocean water becomes the new oceanic crust
• age of rocks:

  Younger rocks are closer to the ridge

  Older rocks are further from the ridge
• Evidence

  Oceanic plate further away from the ridge is being destroyed through subduction

  At that point of subduction, limited sediment accumulation is found

  This tells us that oceanic crusts are usually younger than continental crusts, as older crusts is destroyed further away
• Magnetic striping

  Geographic north and south remains unchanged

  Magnetic North and south shift because the forces that generate earth’s magnetic fields are constantly changing
• Normal polarity is when the magnetic north points roughly at the geographic north
• Reverse polarity is when the magnetic north points roughly at the geographic south
• Magnetic striping

  As a result of the change in Earth’s magnetic North & south, magnetic striping can be observed from the rocks along the seafloor.

  It results in the zebra-like pattern where strips of polarity rocks alternate alongside stripes of reversed polarity rocks.

  This is symmetrical on both sides of the mid-oceanic ridge
• Magnetic striping occurs because the basaltic rocks from the oceanic crusts are volcanic rock formed from iron-rich lava

  Iron-rich lava contains magnetic properties

  The magnetic materials would record evidence of the earth’s polarity at the point where magma emerges out of the earth and solidifies during seafloor spreading
• rock patterns

  The zebra-like patterns is symmetrical on both sides of the mid-oceanic ridge and is repeated over millions of years

  This support plate tectonic theory

  Lava contains magnetic properties

  Lava that solidifies during seafloor spreading would record evidence of magnetic polarity

  Hence, would point to the reverse in magnetic polarity every few millions of years
• Divergent plate movement

  where the plates move away from each other
• Convergent plate movement

  where plates move towards each other
• Transform

  where plates move past each other
• oceanic-oceanic divergence

  when two oceanic plates move away from each other, seafloor spreading occurs

  Magma from deep within the earth rises through the gap in the surface

  This magma that rises up will be cooled and solidified by the cool ocean water to become the new oceanic crust.
• Continental-Continental divergence

  Tensional forces causes two continental plates to move apart

  This leads to the formation of V-shape fault lines within the rocks

  With continuous divergence, the central block will sink forming a deep rift valley with steep sides.

  The decrease in overlying pressure may cause parts of the underlying mantle to melt, forming magma, which may rise through the weak areas in the crust to form volcanoes
• Oceanic-Oceanic convergence

  When two oceanic plates converge, one subducts under the other.

  A subduction zone forms, creating a deep oceanic trench.

  The subduction of the oceanic plate causes the solid mantle material to melt and magma is formed.

  The magma rises through the mantle and ocean floor to emerge as volcanoes.

  Eventually a chain or arc of islands called island arc is formed.

  Friction along the subduction oceanic plate also causes earthquakes to occur.
• Oceanic-Continental convergence

  When an oceanic plate converges with a continental plate, the denser oceanic plate will subduct under the less dense continental plate.

  A subduction zone forms, creating a deep oceanic trench along the plate boundary.

  The subduction of the oceanic plate causes the solid mantle material to melt and magma is formed

  The magma that rises through the mantle and crust to emerge as volcanoes on land.

  The edge of thick continental plate buckles to form fold mountains.

  Earthquakes are also common here due to the huge force of the subduction.
• Continental-Continental convergent

  When two continental plates converges

  They resist subduction as they have similar light densities

  Instead, the plate buckle and fold, forming fold mountains.

  Earthquakes would also occur here due to the friction along the convergent plate boundary.
• Transform plate boundaries

  Plate slide past each other

  As the do so, tremendous stress builds up

  This stress is eventually released, often as a violent earthquake

  No crust is created or destroyed

  Magma does not rise to the Earth's surface, so no volcanoes are formed
• Earthquake is a vibration in the earth's crust caused by sudden release of the stored energy in the earth's lithosphere
• Earthquakes occur when there is plate movement along plate boundaries.

  Plate movement causes the slow-build of stress within the deep fractures of the rocks, known as faults

  When the rocks can no longer withstand the increasing stress, they can suddenly slip many metres into a new position

  This sudden movement causes the seismic wave to be released resulting in the ground shaking
• An earthquake releases energy in the form of seismic waves

  Seismic waves radiate out from a point of sudden energy release called the focus

  The focus is the origin of the earthquake

  The point of the earth’s surface directly above the focus is the epicentre
• earthquakes measured

  Seismometers are used to measure the magnitude of an earthquake

  greater seismic energy, greater the magnitude
• Ricther scale

  Calculates earthquake magnitude by the height of the largest wave recorded on the seismometer

  Limitations

  Underestimates the overall energy released by longer earthquakes by rating them lower magnitudes even when they are likely to do more damage. Therefore, in recent times, Richter scale is only used for small, local earthquakes
• Moment magnitude scale

  Rates earthquake magnitude based on the total amount of energy released during the earthquake

  It is generally more accurate, especially with earthquakes magnitude of 8 and above
• volcanic eruptions

  Volcano is formed when lava erupts on to the earth’s surface, forming cone-shaped mountain. Process of eruption repeats overtime causing lava accumulation, which allows the volcano to build up in size
• Divergent plate boundaries

  When plates move apart from each other, the crust stretches, forming fractures. Magma contains dissolved gases making it less dense than the surrounding materials. It would then rise up to the surface through the fractures within the Earth’s crust. Erupt as lava, causing a volcanic eruption. The lava cools and solidifies overtime forming a volcano
• convergent plate boundaries

  when plates move towards each other, the denser plate subducts under the less dense plate. The subducted crust will be melted by the surrounding mantle, forming magma. Magma contains dissolved gases, making it less dense than the surrounding materials. It would rise up through the fractures in the earth’s crust. Erupt as lava, causing a volcanic eruption. The lava would cool and solidify overtime, forming a volcano
• High-silica lava

  Higher viscousity traps gases more easily which would build up pressure below the earth’s surface

  As magma rises to the earth’s surface the gases expand which causes an outward explosion

  lava, ash, rocks fragments and gases are ejected
• Low-silica lava

  Lower viscousity allows gases to escape easily and flows easily making a less explosive volcanic eruptions. Forming a thin crust
• High volcano with a slightly concave profile. Secondary cones may develop as magma from the vents seeps into the sides of the cone and erupts. Forms from high-silica lava
• Generally low volcano with gently sloping sides and a broad summit. Forming from low-silica lava
• Stratovolcano

  High viscousity magma rises through the fractures in the crust and erupts explosively as lava, ash and rocks

  Ash and rocks settle on the side of the volcano and are later covered by lava

  Successive eruptions would lead to alternating layers of ash and lava

  Highly viscous lava travels short distances before cooling giving rise to steep sides and a narrow summit.
• shield volcano

  Low viscousity magma rises through the fractures in the earth’s crust and erupts gently.

  Successive eruptions would lead to layers of lava accumulating

  Less viscous lava travels long distances before cooling and solidifying, giving rise to gentle sloping sides with a broad summit.
• Volcanic Explosivity Index(VEI) measure the magnitude of volcanic eruptions based on

  The amount of volcanic material ejected

  The height of volcanic cloud

  The duration of the eruption