Geography : Plate Tectonics (Topic 5)

Link to Quizlet here.

3.1 – Location and characteristics of tectonic activity

a. World distribution of earthquakes and volcanoes

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tectonic-plates

Tectonic plates occur in bands. A linear band of earthquakes down the centre of the Atlantic is called the Pacific Ring of Fire.

b. Reasons why earthquakes and volcanoes occur (through the explanation of plate tectonics and hotspots)

Plate movement causes 3 things:

– Tsunamis (earthquakes under the ocean)

– Volcanic erruptions

– Earthquakes

Plate Tectonic Theory:

  1. The earth’s surface is divided into small and large slabs of rock (earth’s crust)
  2. Plates ‘float’ on magma in the mantle
  3. This movement is caused by convection currentsplate2-s9t7h6.png

2 Types of crust:

Oceanic crust: 5-10 km thick, high density material eg. Basalt. An example of oceanic crust is the Pacific Plate.

Continental crust: 25-100km thick, low density material eg. granite. An example of continental crust is the Eurasian plate.

Asthenosphere: below the mantle

Lithosphere: everything above the mantle

Formation of Earthquakes:

  1. Plates move. Initially it is slow – few cm/year
  2. Huge stresses that the plates are under by convection currents make the rock break suddenly as tension is released from the crust
  3. This sudden break causes brief but violent shakng of the ground above.
  4. This violent shaking is the earthquake

Formation of Volcanoes:

  1. Molten magma rises through the cracks of weaknesses in the Earth’s crust, often at hotspots such as Hawaii, or destructive and constructive plate boundaries.
  2. Pressure builds inside the Earth
  3. When this pressure is released as a result of plate movement, magma explodes causing a volcanic eruption
  4. The lava cools to form a new crust
  5. Over time, after several eruptions, the rock builds and a volcano forms.

c. Characteristics of convergent, divergent and conservative plate boundaries.

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d. The measurement of earthquake magnitude (the Mercalli and Richter scales) and diagrams, showing characteristics of focus and epicentre.

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  • Energy is released from the earthquake by seismic waves (Waves spread from the focus)
  • Waves are felt strongest at the epicentre but the loose energy (become less strong) the further away you get – hence the most damage that is done is at the epicentre
  • There are two different scales to measure earthquake magnitude:
  • Richter scale – Measures the strength of energy by the amount of energy released, measured by a seismograph and recorded by a seismometer
  • Mercalli scale – measures the impact of a scene by it’s visual damage, measured in Roman numerals so there is no confusion between the Richter and Mercalli scale.

 

3.2 – Management of the effects of tectonic activity

a. Reasons to why people continue to live in areas of tectonic activity

CASE STUDY: California, USA

  • Population densities have build up over centuries and have many advantages to continue expanding
  • California has a highly developed tech industry (with big names such as MIT Uni, Apple and Google) and offer many HIC jobs
  • 23,000 factories employ 700,000+ people
  • Standard of living is incredibly high – the GDP/ Capita is $60,000 (2014)
  • Attractive landscape and pleasant climate – picturesque coasts provide world renoun surf spots, highest temperature in the summer is 30°c and lowest in winter is 10°c. Rainfall is 300-400mm /year.

CASE STUDY: Iceland

  • Benefits to living in an area might outweigh the risk – for example Iceland’s heating system is totally geothermal from volcanic activities
  • This is very economical, and 25% of Iceland’s electricity production comes from geothermal energy.

CASE STUDY: Sicily, Italy

  • Farmers are able to grow olives, grapes and citrus fruits on the slopes of an highly fertile however active Mt Etna.

CASE STUDY: Philippines 

  • LIC has little to no education on the science behind volcanic activity; many believe that it may be fatalistic
  • Those which live on the slopes of Mt. Pinatubo grow rice and crops; agriculture is the country’s main source of income

CASE STUDY:Montserrat, West Indies

  • The volcano of Montserrat provides 5,000 jobs – 5% of the country’s earnings due to dark tourism
  • People will continue to live in these areas and work, despite the risk.

b. Causes and effects of an earthquake on people and the environment

Case Study: Haitian Earthquake of 2010

Immediate effects:

  • 1/3 of the buildings fell (300,000)
  • 1/4 million people injured (250,000)
  • 200 thousand people died
  • All public services (eg. hospitals, communication lines, police stations) were damaged
  • 1.3 mill homeless
  • Mass paternal and maternal loss
  • Police in chaos, mass looting

Background info:

  • Population of 9.8 mil, 6 mil under the poverty line, 8 mil after the quake
  • Haiti sits on the Caribbean and North American plate boundaries – a conservative plate boundary
  • Haiti is an LIC – none of the buildings were built to cope with earthquakes – this was why the majority of injuries were crush injuries
  • Haiti’s buildings were built on steep slopes and had no foundations because people were not educated enough to build properly
  • Haiti had little to no infrastructure and had poorly equipped emergency services – couldn’t rescue people
  • Haiti had no resources to bounce back from an earthquake – over 1/2 of the population lived below the poverty line and were often unemployed and underemployed.
  • Sewage lies open as well as rusty, unsanitary zinc pipes deliver ‘clean’ water to Haitians – this contributes to an already increased level of disease.

Short term effects and responses:

  • Peace was kept from UN peacekeeping soldiers
  • Oxfam provided camps, food and water purification tablets
  • Many thousands suffering from crush injuries, loss of life and joblessness

Medium term impacts and responses:

  • 300,000 people in recovery camps
  • Urgent need for food and fuel
  • Handicap limits people to work
  • Lack of work increases desperation, increasing theft and criminal activity
  • 9 months after the quake, there was a cholera outbreak leading to 600,000 cases and 8,000 deaths
  • It cost $2 bn to eradicate the disease

Long term and future planning:

  • Prepare for earthquakes with earthquake simulations
  • Question of economics – now there is 80% of the population living under the poverty line
  • Oxfam (NGO) provides microcredit schemes as well as monthly allowances to become more quake resistant for the future
  • As most of Haiti’s food is imported, local farmers are educated by Oxfam to increase yield
  • Water sources are improved so that no metal parts come into contact with the water
  • The importance of hygiene and sanitation is educated
  • Oxfam trains locals on how to build quake resistant housing
  • Unfortunatley it is cheaper to build on the outskirts  – people must travel to find work –> travel is expensive and often exceeds the daily wage.

c. Prediction and prevention of the effects of volcanic eruptions and earthquakes

Prediction of Volcanic Eruptions

  • Yellowstone, USA – use GPS technology to check the bulging of the volcano as magma rises
  • Mt. St Helens, Washington, USA – by checking the composition of gases in the air, you may be able to gage activity of magma below the surface
  • Looking at historical records to see if there is a pattern of eruptions that could repeat
  • Geothermal monitoring from space records changes in heat as magma rises to the surface.
  • Seismic monintoring ‘listens’ as the blobs of lava rise to the surface – they often cause minor quakes.

Prediction of Earthquakes

  • Noting strange animal behavior – this is often reported before quakes
  • Monitoring electrical discharge, there has been evidence that they increase before quakes
  • Recording minor tremors  as many major quakes are preceded by small preshocks
  • Due to the nature of quakes happening instantly, it is very hard to predict earthquakes.

Prevention of effects of Volcanic Eruptions

  • Spraying the lava with water helps it to cool down, solidify and stop flowing. As lava has different consistencies (therefore different speeds at which it flows), this may be a valuable tactic
  • Digging ditches to divert for the lava to flow away from areas at risk
  • Putting concrete/rock barriers in the path of lava, diverting flow
  • Mapping out zones for where lava can flow (like flood wash plains)
  • Setting off explosives to divert lava flow

Prevention of the effects of Earthquakes

  • Providing education for local residents on how to prepare and react to an earthquake – eg. must have 3 days supply of water, torch, batteries and canned food
  • BUILDING DESIGN – ‘Earthquakes don’t kill people, buildings do.’
  • Earthquakes are above the ground moving under the building – hence ‘base isolation’ – rubberised foundations that move under the building as the ground shakes
  • California, USA – many houses are build out of wood as it is flexible. However, when electricity comes into contact with wood, fires ensue.
  • Narita Airport, Japan – Hydraulic shock absorbers
  • Square corners are weaknesses – ‘corner brace’ to strengthen the corners with additional wood or metal. Cylindrical housing (especially in rural areas) is often used as there are no stress points
  • CASE STUDY  – Transamerica Pyramid, San Francisco, USA
  • Building built to withstand earthquakes of a magnitude of 7
  • 1984 Californian earthquake, it swayed over 30 m and still stayed in place due to it’s wide, triangular, stable base.

 

 

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