earthquakes and volcanoes

• Continental drift: The theory that the continents have moved over time.
• Types of plate boundaries:

  • Constructive (divergent) - away from each other.
  • Destructive(convergent) - towards each other.
  • Conservative (passive) - slide past each other.
• Layers of the earth:

  • Crust
  • Mantle
  • Outer core
  • Inner core
• Constructive (divergent):

  2 plates move apart due to convection currents in the mantle. A gap is created, magma or lava rises through gap to reach the surface and forms islands.
• Conservative e.g. San Andreas Foult:

  2 plates slide past each other along a fault (line of weakness), the plates are moving in different directions and different speeds, friction causes plates to lock together, this builds up pressure they suddenly move and pressure is released as an earthquake.
• Destructive e.g. Nazca and south American Plate:

  Oceanic Nazca plate subducts under Continental S. American plate as it is denser, creates a subduction zone. Friction and heat is created and the oceanic melts to magma. Magma builds up and rises through small cracks to explode as a volcano.

  At subduction zone pressure builds and sometimes leads to violent earthquake.
• Composite volcano: violent, cone-shaped, ash and lava, non-frequent.
• Shield volcono: gentle-sloped, made from runny magma. These produce 'quiet' eruptions, frequent. Constructive plate margins.
• Volcanoes:

  • Openings in the earth's crust are created at most plate boundaries where molten rock and gases reach the surface.
  • They are surrounded by a cone of ash and lava.
• 3 types of volcanoes:

  • Active - regular eruptions.
  • Dormant - not erupted for many years but activity can be detected inside.
  • Extinct - will not erupt again as no activity is detected.
• Global distribution of volcanoes:

  • In belts/ lines.
  • On/near plate boundaries/where plates meet.
  • On destructive margins/ where plates move towards each other.
  • E.g. Mid Atlantic Ridge
  • Hotspots.
  • On constructive margins/where plates move apart.
  • E.g. Pacific Ring of Fire.
• Geosynclines: when sediments settle on the floor in depressions.
• Anticlines: where rocks are folded upwards.
• Synclines: where rocks are folded downwards.
• Nappes: severely folded and faulted rocks.
• Over folds: when folds are pushed over one side.
• Ash fall/tephra fall:

  • Can cause poor or low visibility.
  • Loss of agricultural land.
  • Dangerous for aircrafts, engines can fail.
  • Carrying of harmful gases, salts and heat.
• Pyroclastic flows:

  • Destroy anything in its path by direct impact.
  • Burn sites with hot rocks debris.
  • Burn forests, farmlands, destroy crops and buildings.
  • Deadly effects include asphyxiation (inhalation of hot ash and gases), burial, incineration (burns) and crushing from impact.
• Lahars: rapidly flowing thick mixture of volcanic sediments (from the pyroclastic materials) and water.
• Volcanic hazards can be classified into:

  • Primary hazards: direct hazardous effects related to the eruptions e.g. lava flows, pyroclastic flows, ashfalls etc.
  • Secondary hazards: indirect hazardous effects related to the eruptions triggered by primary hazards e.g. lahars, acid rain, landslides etc.
• A volcano formed in Montserrat because the boundary where Montserrat lies is where the continental (land) Caribbean plate meets the oceanic (sea) Atlantic plate. This is called a destructive boundary because the heavier oceanic plate is forced under the lighter continental plate and is destroyed.
• CS: Volcanic Eruption, Montserrat:

  • Montserrat lies on a destructive plate margin.
  • The continental (land) Caribbean plate meets the oceanic (sea) Atlantic plate.
  • The heavier oceanic plate is forced under the lighter continental plate.
  • This is called a subduction zone.
  • Oceanic plate melts due to pressure and heat and becomes magma.
  • Magma is released through cracks in the continental as a violent strato volcano.
  • Most people live here as the land around the coast is flat and very fertile. Excellent for growing crops. In the north it is mountainous.
• CS: Volcanic Eruption, Montserrat:

  Primary effects:

  • 2/3 of the island was covered in ash.
  • 50% of the population were evacuated to the north of the island to live in the makeshift shelters.
  • 23 people died in 1997.
  • Plymouth - the capital became a ghost town.
  • Floods as valleys were blocked with ash.
• Negatives of living near a volcano:

  • Destroying buildings.
  • Destroying crops.
  • Destroying bridges, roads, railways... therefore disrupting communication
  • Ultimately they can kill people if the response is not managed well.
• Positives of living near a volcano:

  • Ideal for farming - lava forms nutrient rich soil that can be cultivated to produce healthy crops and high yield harvests.
  • The soil naturally contains potassium, nitrogen and sulphur.
• Geothermal energy:

  • Geo (the earth) thermal (heat).
  • Steam is used to turn turbines in geothermal power station.
• Tourism:

  • Creates jobs for local people in tourism. One hour flight to volcano costs 310 euros per person.
  • Work in hotels i.e. Hotel Ranga run daily trips over the volcano, restaurants and gifts shops.
  • Locals employed as tour guides.
  • Apart from the volcanoes, hot springs or geysers attract tourists e.g Blue Lagoon, Thorsmork hot springs, hraun-foss (lava water fall).
• Mining: lava from deep within the earth contains minerals which can be mined once the lava has cooled (gold/silver/diamonds).
• How a volcano can be predicted:

  • By monitoring earthquake activity scientists get a good idea if a volcano will erupt.
  • Measuring sulphur content of local springs and rivers we can see if volcanic activity is increasing.
  • Using a tiltmeter - measure the angle of the volcano and work out the likelihood of it erupting
  • Geothermal imaging - helps get an image of the volcano.
  • Observing gas emissions - extra time given before it erupts.
• CS: Sichuan Earthquake 2008, China:

  • The Sichuan Earthquake caused some areas to be cut off by landslides and building collapses.
  • A total of 5 million buildings collapsed including Juyuan middle school in Dujiangyan, killing 900 people.
  • 11 milion people were made homeless and 374,000 people injured.
  • In Shifang, chemical plants collapsed, killing hundreds and releasing toxic ammonia.
  • Power and water supplies cut off.
  • Rivers flooded because landslides had blocked them.
  • Death toll was 69,000 and 18,000 people missing.
• Epicentre: point on the earth where the quake is felt directly above the focus. The greatest force is felt here.
• Focus: within the earth's crust - where the earthquake begins.
• Seismic waves: a wave/vibration which travels within the earth, through the rocks.
• Why people live in earthquake zones:

  • Lived there all their lives.
  • Close to family/friends.
  • Have good services/schools/hospitals.
  • Can't afford to move.
  • Confidence in safety of buildings.
  • Willing to take the risk; as earthquake has not occurred for many years.
  • Have a job there.
• Why quakes in LEDCs have worse impacts than MEDCS:

  • Poor quality buildings in LEDCS which easily collapse.
  • Building regulations are not enforced.
  • High population densities so more people die.
  • Poor medical services/hospitals so people can't be properly treated for their injuries.
• • Prediction: trying to forecast when an earthquake will happen.
  • Protection: constructing buildings so that they are safe, to an appropriate standard and using designs to withstand movement.
  • Preparation: organising drills and codes of practise so that people know what to do in case of emergency. e.g. hospitals, emergency services and inhabitants practising for major disasters.
• Buildings:

  • Pyramid shape: great in an earthquake. Storeys swayed a bit but didn't fall down.
  • Shock absorbers: giant rubber pads used to soak up shock waves. Build them under a wall and it reduces shaking.
  • Beehive shape: short and squat and keeps its feet firmly on the ground.