QUESTION 3 - ACTIVE ZONES

QUESTION 3 - ACTIVE ZONES

Key areas of study for this question:

  • Plate boundaries
  • Plate tectonics and landforms associated
  • Volcanoes Case Study - Mt. St. Helens (USA)
  • Volcanoes Case Study - Mt. Pinatubo (Philippines)
  • Earthquakes Case Study - Kobe, Japan
  • Earthquakes Case Study - Izmit, Turkey
  • Living in areas of risk
  • Prediction and prevention

PLATE BOUNDARIES

The structure of the earth consists of 3 main areas: crust, mantle and core.

The crust- this is the surface of the earth (100-200km thick). This is a very thin layer of brittle rock, with cracks running all around it (like a cracked boiled egg shell).
 
The mantle- this is the goo-ey area inside the crust although it is solid rock it is so hot that it acts like toffee moving around beneath the crust.
 
The core- This is a solid ball of iron at the centre of the earth. The core is extremely hot (7000°C).
 
crust-mantle-core.gif
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

 

 

 

 

Tectonic plates act like rafts on the hot soft mantle below and are actually moved around by the convection currents (heat) below. As a result they are actually moving. Sometimes they collide, slide past each other and sometimes move away from each other.

 

CONTINENTAL DRIFT

In 1912, a German scientist called Alfred Wegener proposed that South America and Africa were once joined together and had subsequently moved apart. He believed that all the continents were once joined together as one big land mass called Pangaea and this was intact until about 200 million years ago. The idea that continents are slowly shifting their positions is called continental drift.

Evidence of continental drift:

  • Study of fossils - similar fossils are found on different continents. This is evidence that these regions were once very close or joined together.
  • Shapes of continents - some continent look like they may have once fitted together (e.g. South America and Africa)

 

 

PLATE TECTONICS

Wegener knew the continents had drifted but he couldn't explain how they drifted. It wasn't until the 1960's that geologists used ocean surveys to explain continental drift with the theory of Plate Tectonics.

What is Plate Tectonics?

  • The Earth's surface is made up of a number of large plates (like pieces of a jigsaw puzzle) that are in constant, slow motion.
  • The ocean floors are continually moving, spreading from the centre and sinking at the edges.
  • At the edges of these plates (plate boundaries) earthquakes and volcanoes occur.
  • Convection currents in the mantle move the plates. The source of heat driving the convection currents is radioactive decay which is happening deep in the Earth.

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PLATE MARGINS:

CONSTRUCTIVE (DIVERGENT) -  (Examples include North American and Eurasian Plates)

  • This is where plates move away from each other.
  • Where 2 oceanic plates move apart, ocean trenches are formed and undersea volcanoes form mid-ocean ridges, such as the Mid-Atlantic Ridge.
  • Where continental plates pull apart, rift valleys are formed and lava erupts to create shield volcanoes.
  • Minor earthquakes can occur.

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DESTRUCTIVE (CONVERGENT) - (Examples include Pacific/Nazca and South American Plates)

  • This is where plate push together.
  • The denser (heavier) oceanic plate is forced down into the mantle (called subduction). This forms an ocean trench.
  • The lighter continental crust, is compressed to form fold mountains such as the Andes.
  • As the oceanic plate sinks, it melts and the molten magma finds its way to the surface in explosive volcanoes.
  • Earthquakes can occur when the plates move.

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CONSERVATIVE (TRANSFORM) - (Examples include Pacific and North American Plates)

  • This is where plates are pushed in different directions e.g. San Andreas Fault.
  • Plates remain locked together until the rock breaks along a fault line.
  • Major earthquakes occur as stored energy is released.

 

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COLLISION - (Examples include African and Eurasian Plate)

  • Collision boundaries occur when two plates of similar densities move together (e.g. a continental plate and a continental plate).
  • This causes the material between them to buckle and rise up, forming fold mountains.
  • The Himalayas are an example of a chain of fold mountains. They have been formed by the African plate colliding into the Eurasian plate.

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lesson-1-boundaries-and-features.doc lesson-1-boundaries-and-features.doc

 

MAKE SURE YOU KNOW WHAT ALL THESE KEY WORDS MEAN.

  • MID-OCEAN RIDGE - A series of mountain ranges on the ocean floor, more than 84,000 kilometers (52,000 miles) in length, extending through the North and South Atlantic, the Indian Ocean, and the South Pacific. According to the plate tectonics theory, volcanic rock is added to the sea floor as the mid-ocean ridge spreads apart.
  • RIFT VALLEYS - Steep sided valley found on the Earth's surface created by tectonic rifting.   
  • SHIELD VOLCANOES - Volcano created from alternate layers of lava flows. Shield volcanoes are slightly sloping.
  • SUBDUCTION ZONE - Subduction is the process that takes place at destructive boundaries by which one tectonic plate moves under another tectonic plate and sinks into the mantle.
  • OCEAN TRENCH - Deep depression found at the edge of the ocean floor. Represents area of tectonic plate subduction.
  • FOLD MOUNTAINS - Fold mountains are mountain ranges that are formed when two of the tectonic plates that make up the Earth's crust push together at their border. The extreme pressure forces the edges of the plates upwards into a series of folds.

VOLCANOES

Volcanoes occur when there are weaknesses in the earth's crust, allowing magma, gas and water to erupt onto the land and seabed. Most volcanoes occur at plate margins. Hotspots are places where the crust is thin and magma may be able to reach the surface of the earth (e.g. Hawaii).

Volcanoes can be classified into the following categories:

  • Active - volcanoes that have recently erupted.
  • Dormant - volcanoes that have not erupted in a long time ('sleeping').
  • Extinct - volcanoes which there has been no record of tectonic activity.

Another way of describing volcanoes is according to their shape.

  • Shield volcanoes - found at constructive plate margins and above hotspots. Here, the lava is hot and runny, following long distances before solidifying. Shield volcano eruptions are gentle oozings of lava, which form large cone shaped mountains, like Mauna Loa in Hawaii and Surtsey in Iceland.
  • Composite volcanoes - are found at destructive plate margins. Here, the lava is acidic, thick, sticky, and cools quickly. Composite volcanoes experience explosive eruptions of ash, lava and lava bombs, which are cone shaped with steep sides, like Montserrat in the Caribbean and Mount St. Helens in the USA.

 

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CASE STUDY - MOUNT ST. HELENS (USA)

Mount St Helens is on the plate boundary between the Juan de Fuca plate and North American plate. When it erupted in May 1980, it permanently changed the surrounding landscape.

KEY FACTS:

  • Mount St. Helens is located close to Seattle in the state of Washington, USA.
  • Eruption - 18th May 1980.
  • Juan de Fuca plate subducted beneath the North American plate - a destructive plate margin.
  • The eruption had been predicted for some time, so they were pretty well prepared - this was the first time modern technology was used.
  • 57 people died.
  • 250 homes destroyed.

 

lesson-2-volcanoes-mt-st-helens.ppt lesson-2-volcanoes-mt-st-helens.ppt

 

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CASE STUDY - MOUNT PINATUBO (PHILIPPINES)

Mount Pinatuba had been dormant for 500 years. The first sign that this situation might be changing occured on the 16th July 1990 when a magnitude 7.8 earthquake struck about 60 miles northeast of Mount Pinatubo on the island of Luzon in the Philippines. Thousands of small earthquakes occurred beneath Pinatubo throughout April, May, and early June 1991, and many thousand tons of noxious sulphur dioxide gas were also emitted by the volcano.

KEY FACTS:

  • Eruption - 12th-15th June 1991.
  • 2nd biggest eruption this century.
  • 300 people died.
  • 1000's evacuated.
  • 1.18 million people affected.
  • Due to the gas cloud spreading across the world, global temperatures dropped temporarily (between 1991-1993) by approximately 0.5'C.

 

lesson-3-mount-pinatubo-2.ppt lesson-3-mount-pinatubo-2.ppt

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VOLCANIC HAZARDS:

  • LAVA FLOW - Molten rock flowing down the sides of a volcano. Hot basaltic lava from shield volcanoes flows quickly.
  • LAHARS - Mudflows, a mixture of ash and water from melted snow and ice, travel at great speed down the mountain, making evacuations difficult.
  • DUST AND ASH CLOUDS - Ash thrown high into the atmosphere shuts out the sun and, when it settles, can completely bury buildings and crops.
  • LAVA BOMBS - Large pieces of rock and ash are thrown into the air.
  • PYROCLASTIC FLOW - Burning clouds of gas and ash, with temperatures of up to 1000'C, rush down the mountains, scorching everything in their paths.

EARTHQUAKES

An earthquake is the result of vibrations in the earth's crust. These are caused by shock waves travelling outwards from a sudden movement deep within the crust. The source of the shock waves is known as the focus, and the point on the earth's surface immediately above is the epicentre. Most large earthquakes are associated with movements along plate margins but many smaller movements occur at weaknesses in the crust, such as fault lines. The size of an earthquake is measured with a seismograph along the Richter Scale.

 

The impacts of an earthquake will depend on a number of factors:

  • The strength of the earthquake and distance from the epicentre.
  • The nature of surface rock - some rocks 'shake' more than others.
  • The number of people who live in the area.
  • The time of day the earthquake happens.
  • The extent of preparation in an area and availability of emergency services.

 

CASE STUDY - KOBE EARTHQUAKE 1995 (JAPAN)

On 17th January 1995, an earthquake struck Kobe, a heavily populated urban area in Japan. It measured 7.4 on the Richter scale and occurred as a result of plate movement along the boundary between the Philippines Plate, Pacific Plate and Eurasian Plate.

KEY FACTS:

  • The ground shook for approximately 20 seconds.
  • 5000 people died.
  • 3000 people were made homeless.
  • Estimated damage was £100 billion.

 

lesson-4-kobe-earthquake-1995.doc lesson-4-kobe-earthquake-1995.doc

 

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CASE STUDY - IZMIT EARTHQUAKE 1999 (TURKEY)

On 17th August 1999, an earthquake struck Izmit, an industrial city area in Turkey, approximately 55 miles east of Istanbul. It measured 6.8 - 7.6 on the Richter scale and occurred as a result of the Arabian/African plate and the Eurasian plate moving north and south of each other.

KEY FACTS:

  • The ground shook for approximately 35 seconds.
  • Over 17,000 people died.
  • 200,000+ people were made homeless.
  • Millions spent on the damage caused by collapsed buildings etc.

 

lesson-4-turkey-earthquake-1999-1.doc lesson-4-turkey-earthquake-1999-1.doc

 

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EARTHQUAKE HAZARDS:

  • Death / Injuries
  • People left homeless
  • Buildings destroyed
  • Infrastructure destroyed
  • Loss of tourism
  • Tsunami risk
  • Disease breaks out
  • Gas mains / Electricity lines broke.

LIVING IN AREAS OF RISK

Over 500 million people live in active zones around the world despite the risks. The hazards are obvious, so there must be reasons why people continue to live in these areas. Most of the time, the majority of people are able to go about their daily business without worrying about the potential risks.

lesson-5-why-do-people-live-in-areas-of-tectonic-activity.ppt lesson-5-why-do-people-live-in-areas-of-tectonic-activity.ppt

lesson-5-why-live-close-to-tectonic-activity-worksheet.doc lesson-5-why-live-close-to-tectonic-activity-worksheet.doc

 

SOME REASONS WHY PEOPLE CONTINUE TO LIVE IN AREAS OF VOLCANIC ACTIVITY:

  • The dramatic scenery created by volcanic eruptions attracts tourists. This brings income to an area e.g. Iceland and Mount Etna.
  • The lava and ash deposited during an eruption breaks down to provide valuable nutrients for the soil - this makes the soil very fertile, which is extremely good for growing crops.
  • These crops can be sold locally.
  • The high level of heat and activity inside the earth close to the volcano, can provide opportunitites for generating energy. This is called geothermal energy.

 

SOME REASONS WHY PEOPLE CONTINUE TO LIVE IN AREAS OF EARTHQUAKE ACTIVITY:

  • Popular tourist destinations.
  • Tourism provides jobs for local people.
  • Earthquake proof buildings in MIC's and HIC's.
  • Chance of being affected is relatively low.
  • Natural places of beauty.

PREDICTION AND PREVENTION

There is nothing that can be done to stop volcanic eruptions or earthquakes; prevention is not an option. 

 

Predicting volcanic eruptions - Volcanologists use a variety of techniques of monitoring techniques to predict eruptions:

  • Remote sensing - Satellites monitor volcano temperature and gas emissions.
  • Seismometers - These measure the increase in earthquake activity that occurs before an eruption.
  • Tiltmeters - These monitor changes in the shape of a volcano that occur as it fills with magma.
  • Gas emissions - A rise can indicate increased risk.
  • Ultrasound - This is used to detect the movements of magma.

 

Preparing for volcanic eruptions:

  • An exclusion zone around the volcano must be created.
  • Authorities must be ready and able to evacuate residents.
  • Emergency supplies of basic provisions such as food must be gathered.
  • A good communication system needs to be in place.
  • Everyone who could be affected by the eruption needs to be informed.

 

Predicting earthquakes - earthquakes are not as easy as eruptions but there are some ways of monitoring:

  • Laser beams can be used to detect plate movement.
  • A seismometer is used to pick up vibrations in the earth's crust. An increase in vibrations may indicate an earthquake.
  • Radon gas escapes from cracks in the earth's crust before an earthquake. Levels of radon gas can be monitored.

 

Preparing for earthquakes - as prediction techniques are not 100% reliable, preparation is essential:

  • People living in earthquake zones need to know what they should do in the event of an earthquake. Training people may involve holding earthquake drills and educating people via TV or radio.
  • Earthquake drills - e.g. 'Disaster Prevention Day' every 1st September in Japan.
  • People may put together emergency kits and store them in their homes - e.g. first aid items, blankets, tinned food etc.
  • Earthquake proof buildings have been constructed in major cities. They are designed to absorb the energy of an earthquake and to withstand the movement of the earth (usually pyramid shape).
  • Roads and bridges can be designed to withstand the power of earthquakes.

 

lesson-6-prediction-and-prevention.ppt lesson-6-prediction-and-prevention.ppt

 

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Examples of posters in Japan

for Disaster Prevention Day.

 

 

 

 

 

 

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Example of an earthquake proof

building.

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