Common Entrance Revision Tectonic Processes by dfsiopmhy6


									                               Common Entrance Revision
                                  Tectonic Processes

1. The global distribution of earthquakes and volcanoes.
• Know where and why earthquakes and volcanoes are found.
   Volcanic eruptions do not occur just anywhere but are confined to certain areas. Earthquakes
   can occur anywhere but are more common in some places than others.
   Volcanoes occur in narrow belts or small clumps. The belt of volcanoes around the Pacific
   Ocean is called ‘The Ring of Fire’. Earthquakes are also more common along long narrow
   belts. Earthquakes and volcanoes do often occur in the same place in long narrow ‘zones of

2. How earthquakes and volcanoes are related to the boundaries of crustal plates.
• Different types of plate boundary.
   Earthquakes and volcanoes are strongly associated with the boundaries between the large
   plates that make up the earth’s crust.
   A constructive plate boundary occurs when two plates move apart. Molten lava rises in the gap
   to form a long low ridge. Sometimes islands such as Iceland are formed. Iceland is part of the
   Mid Atlantic Ridge, a constructive plate boundary that runs down the middle of the Atlantic
   A destructive plate boundary occurs when two plates move together. Sometimes one plate is
   pushed (subducted) under another. As the plate is pushed under it melted. This molten magma
   moves back up to the surface to form volcanic mountains e.g. The Andes. Sometimes the
   plates get such and the release of friction when they finally move causes earthquakes.
   Another type of plate boundary is a collision zone, which occurs when two continents being
   carried on two plates that are moving towards each other collide. The edges of the continents
   get pushed up to form a mountain range e.g. the Himalayas and the Alps.
   When plates slide past one another it is called a transform fault. No rock is created or
   destroyed instead the plates scrap past one another causing earthquakes. This is happening
   along the San Andreas Fault in California.

•   Movement, friction, epicentre, magma and lava, mountain building.
    Plates move because they are ‘floating on the molten rocks of the mantle which is underneath
    the crust. They only move millimetres a year.
    Friction occurs when two plates try to move past one another. Because they are huge pieces of
    rock they are rough and often get stuck. The release of friction causes earthquakes.
    The epicentre is the point on the surface of the earth above the origin (focus) of an earthquake.
    Magma is molten rock under the ground.
    Lava is molten rock once it reaches the surface.
    Mountain building occurs either when plates collide or when a chain of volcanoes occurs.

3. The nature and causes of volcanoes.
• Plate boundaries.
   Volcanoes most commonly occur at constructive plate boundaries e.g. Iceland and subduction
   zones e.g. Japan. Some volcanoes such as Hawaii occur right away from plate boundaries
   over ‘hot-spots’.
• Volcanic eruptions.
   Some volcanoes erupt almost constantly (active) e.g. Mount Etna, some hardly ever (dormant)
   e.g. Mount St Helen’s, and some never (extinct) e.g. Snowdon. Gentle regular eruptions
   (Hawaii) tend to cause less damage than sudden, unpredictable eruptions (Mount St Helen’s).
4. Volcanic landforms.
• Different types of cone.
   When lava is thick and runny, or fluid, the gases escape easily and the eruptions are not so
   violent. The lava can flow a long way before it cools and turns solid. Volcanoes like this with
   gentle slopes are called shield volcanoes e.g. Mauna Loa, Hawaii.
   Volcanoes with sticky lava erupt violently. The lava does not flow far, and lots of dust and ash
   are emitted. A steep-sided cone volcano is formed e.g. Paricutin, Mexico.

•   Craters, calderas, lava flows, and types of lava.
    A crater is a roughly circular shaped bowl opening at the top of a volcano.
    A caldera is a huge crater that is left after the top of a volcano is blown off in an eruption.
    Lava can be runny and very fast flowing. This type of lava tends to flow in a channel. Other
    types of lava are thicker and much slower moving but tend to spread out over the countryside.

5. The effects of volcanoes.
• Physical effects – landscape, climate, vegetation.
   Volcanoes can completely devastate the landscape. Mountains can be built or destroyed,
   valleys blocked, lakes formed, and rivers diverted.
   Volcanoes can blast thousands of tons of ash and dust up into the atmosphere. This can alter
   the climate by blocking out the sun. It can also increase rainfall. Volcanic dust can circulate
   around the world in a couple of days.
   Vegetation is destroyed by volcanic eruptions. But as the cold lava breaks down it leaves a
   very fertile soil, which is excellent for plant growth.

•   Human effects – buildings, farms, roads, and deaths.
    Some volcanoes are very destructive and destroy large areas of buildings and farmland. Mount
    St Helen’s destroyed every tree within 25km. 22,000 people were killed when an avalanche of
    ash and mud swept down Nevado del Ruiz in Colombia.
    But volcanoes can be good. The fertile soil made from eroded lava is very fertile and good for
    farm crops.

6. How humans respond to the volcanic hazard.
• Predicting volcanic eruptions.
   Vulcanologists try to predict volcanic eruptions by using equipment such as tiltmeters and
   seismometers as well as analysing the gases that escape before eruptions. Although these can
   be useful it is difficult to be exact.

•   Evacuation plans.
    Many volcanic areas have evacuation plans. Half the island of Montserrat had to be evacuated
    in the late 1990’s because of the continuing eruption of the volcano that had not erupted for
    400 years.

•   Preventing eruptions or diverting lava flows.
    Farmers of the island of Sicily have attempted to divert the lava flows from Etna by building
    diversion channels or by dropping large blocks of concrete from helicopters to dam lava flows.

3. The nature and causes of earthquakes.
• Plate boundaries.
   Earthquakes occur along all types of plate boundary. Small earthquakes occur near
   constructive plate boundaries. Larger earthquakes occur at subduction zones, collision zones
   and transform faults. This is because more pressure and friction build up, the release of which
   is the earthquake.

•   Epicentre depth; Richter Scale.
    The epicentre is the point on the surface of the earth above the origin (focus) of an earthquake.
   The Richter Scale is a way of measuring the intensity of an earthquake. An earthquake of 4 on
   the Richter Scale would hardly be felt, an earthquake of 7.5 or 8 would result in complete

4. The effects of earthquakes.
• Physical effects – landscape, faults, fire.
   The shaking of the earth can cause large landslides. When combined with water these can be
   Earthquakes create cracks in the ground called faults. When the rock on one side of a fault
   moves it can put different rocks against one another. When these rocks are eroded they create
   different landforms.
   Fire often results from earthquakes destroying large areas of countryside.
• Human effects – buildings, roads, communications, emergency services, deaths.
   Buildings and bridges crack and topple. Roads split open, elevated roads collapse. Gas pipes
   fracture, and electricity wires get torn down. These cause fires. Landslides may block roads.
   Water mains burst which means no water. At home, cookers and heaters fall over and start
   fires. Ceilings fall down. Doors jam. Everything slides off shelves and tables.
   Transport comes to a standstill and communication is very difficult. Hospitals and ambulance
   stations may be damaged hampering rescue.
   The after shocks may be as big as the original earthquake causing more damage.
   Many people may die either directly in the earthquake, in fires caused by the earthquake or in
   the days that follow from injury, hunger and disease.

5. How humans respond to the earthquake hazard.
• Predicting earthquakes.
   Many plate boundaries are closely monitored and their movement recorded. This helps to
   identify where pressure is building up and where an earthquake is likely to occur. Tiny cracks
   appear in rocks just before an earthquake and can be measured using a tiltmeter. Water levels
   may change, radon gas may be given off and there may be foreshocks felt just before and
• Evacuation and emergency plans.
   Most developed countries in earthquake prone areas have an earthquake plan. An earthquake
   centre may be set up; people told to prepare an emergency kit; earthquake drill is practised in
   schools; people are told about the emergency plan; and emergency services are prepared.
• Building design.
   Buildings in earthquake prone zones are built to withstand a large shock. Buildings and bridges
   are designed to sway rather than snap. Some buildings are built with giant shock absorbers to
   limit earthquake damage.
   Richer countries can afford to be better prepared than poorer countries.


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