Earthquakes and volcanoes

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Structure of the Earth

The earth consists of 4 main layers:

  • The crust is the outer layer, broken into sections caled tectonic plates. It is the thinnest layer and the one which we live on.
  • The mantle is the thickest layer and consists of molten rock
  • The outer core is molten & about 3000 degrees C.
  • This inner core is solid due to the immense pressure and is about 5000 degrees C.
  • Both the inner & outer core consist of iron & nickle.

Task

Draw and label a diagram showing the earths structure
Structure of the earth
Figure 2.1.4: Structure of the Earth

Tectonic Plates

Plate Movement

The earths crust is broken into different sections which are slowly moving about.

Convection currents in the mantle distribute the heat from the core. This movement drags the plates in different directions and is responsible for earthquakes and volcanoes.

Over millions of years the land masses that we are familiar with have moved around the planet as the tectonic plates shifted about.

Where the different sections of tectonic plate meet the movement causes geographical features such as mountains, volcanoes and earthquakes.

Video 2.1.1: Convection currents and plate movement

Constrcutive Boundaries

  • Convection currents in the mantle drag the plates apart.
  • Magma rises to fill the gap and solidifies to form new crust.
  • As the process repeats a ridge is formed and this slowly gets wider as the plates continue to seperate.
  • Example: the Mid-Atlantic Ridge.
  • This creates fissure volcanoes which are long cracks, they are less explosive.
Constructive boundary
Figure 2.1.6: Constructive boundary

Destructive Boundaries

  • Oceanic & continental plates collide. The oceanic plate is denser and so sinks under the continental plate.
  • As the oceanic plate sinks it takes some sand, water and other materia from the sea bed with it. This melts and is gaseous which causes it to force its way up to the surface as a volcano.
  • The continental plate crumples at the edge creating fold mountains in addition to the volcanoes.
destructive boundary
Figure 2.1.7: Destructive boundary

Collision Boundary

  • Convection currents in the mantle pull two plates of continental crust together.
  • Since both crusts are made of the same material and have equal density neither subducts. They crumple up.
  • This process creates fold mountains. There are no volcanoes at these boundaries but earthquakes occur.
  • Example: the Himalayas.
collision boundary
Figure 2.1.8: Collision boundary

Types of Volcano

  • Shield: gentle sloping, created by basic lava (travels along way before solidifying). Found at constructive boundaries.
  • Composite: alternating layers of acid lava & rock/ash create the classic conical shape. Found at destructive boundaries.
  • Ash & cinder: Alternating layers of ash & cinder compacted.
  • Fissure: volcanoes running along a crack in the crust, usually a constructive boundary.
  • Caldera: Crater volcano created after volcano collapses in on itself having emptied the magma chamber.
  • Dome: steep sided volcano created by acid lava which cools before it has travelled far.
  • Destructive boundary volcanoes are often cone shaped and explosive.
  • Constructive boundary volcanoes are often more gently sloped and have less violent erruptions.
volcano types
Figure Vocanic Types (source)

Volcanic Features

Objective: be able to correctly label the key features of volcanoes and relate them to the increased risk they pose to human settlements.

  • Volcanoes vary in shape and structure depending on the reason for their existence.
  • Secodary vents (fumaroles) occur when magma and gases force their way through weaknesses in the main volcanic structure.
  • Lava, ash, cinders and smoke may be ejected from the vent.

Tasks

  1. Draw and label a simple diagram of a volcano and the ejected material.
  2. Make simple sketch diagrams showing fissure, dome and ash-cinder volcanic structures.
  3. Using Figure 2.0, describe the location of the Pacific Ring of Fire and explain why this area has this name.
Volcano characteristics diagram
Figure 2.1.2: Volcano Features

Costs & Benefits of Volcanic Environments

Negative Impacts

  • Volcanic eruptions can cause significant damage and loss of life.
  • Lava flows destroy vegetation buildings and roads.
  • Ash can smother plants, cut out light in the atmosphere, disrupt air travel and cause respiration problems for people.
  • Eruptions often cause earthquakes as pressure is released.
  • Volcanoes with ice near the peak, or crater lakes can cause devastating mud flows as the water mixes with loose ash.
  • Gas released from volcanoes can travel down the slopes silently killing people and animals.

Positive Impacts

  • Volcanoes can bring environmental and socio-economic benefits.
  • Fertile soils: ash and lava contain many minerals and nutrients that weather to form fertile soils which can be used very effectively for farming.
  • Sulphur deposits: sulphur is mined and sold by the people living close to volcanoes in Indonesia.
  • Tourism: the volcanic scenery, crater lakes, hot spring and geysers attract tourists and create many job opportunities.

Case Study: Montserrat

Objective: be able to describe the main events and damage caused by the volcano. You should be able to suggest reasons for the extent of the damage.

Montserrat is an island in the Caribbean that unexpectedly suffered devastating eruptions.

Tasks

  1. Using the google map shown to the right, describe the location of Montserrat on a regional scale.
  2. Draw a sketch map showing the location of the Sufriere Hills volcano within the island.
  3. Watch video 2.1.4:
    • Explain the cause of the volcano
    • Describe the main effects/impacts of the eruptions
    • Why did they cause so much damage on the island?
  4. Make a sketch of Figure 2.1 to show the hazard map and restricted zones that are in place on Montserrat since the eruption.
Map of Montserrat
Video 2.1.4: Montserrat eruption
Montserrat hazard map
Figure 2.1: Hazard Map of Montserrat after the eruption

Earthquake Characteristics

  • Focus: the exact point at which the earthquake occurred- often deep in the ground.
  • Epicentre: the point on the surface of the earth directly above the focus (so it can be located easily on maps).
  • Seismic waves: these are the shockwaves that move outwards from the focus. Their energy disipates the further they travel.
  • Seismometer: instrument that measures the magnitude of earthquakes.
earthquake characteristics
Figure 2.1.2: Earthquake features

Risk factors and Earthquakes

Objective: Demonstrate an ability to to identify factors that can affect the scale of a disaster and be able to link them to levels of development.

Tasks

  1. Watch Video 2.1.2
  2. Describe why older building tend to suffer more damage in earthquakes than newer ones.
  3. Why do buildings built on soft land suffer more than those with foundations on rock?
  4. Why can hospitals outside towns add to the problems?
Video 2.1.2: Anatomy of an Earthquake

Measuring Earthquakes

  • Seismometer: a machine that records vibrations in the earth.
  • Seismograph: the print out/graph produced by the seismometer.
  • Richter scale: the sale traditionally used to record the magnitude of an earthquake.
  • Movement Magnitude Scale: the scale often used currently to record the magnitude of earthquakes (it is more accurate for large earthquakes than the Richter scale.

Case Study: Haiti

Cause & Effect of the Haiti Earthquake

Objectives:

  • Understand the cause of the Haiti earthquake.
  • Demonstrate an ability to interpret information shown in photographs.
  • Demonstrate analytic and reasoning skills in relation to development and disaster impacts.

Tasks

  1. Describe the location and cause of the earthquake.
  2. Go to this page BBC bitesize. Describe the key facts about the damage it caused.

Responses to the Earthquake

Tasks

  1. Watch Videos 2.1.3 and 2.1.4
  2. Go to these links Guardian: Haiti 2015 and Haiti then & now.
  3. How well has Haiti recovered from the earthquake?
  4. Describe three reasons why there are still lots of problems in Haiti 5 years on from the earthquake.

Extended Writing Task

Explain why the less developed a country is the more it is likely to suffer if an earthquake occurs. (you should write about a page in your book to answer this. Factors to include: preparation, emergency response, rebuilding/reconstruction.

Video 2.1.3
Video 2.1.4