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Tectonic hazards

Tectonic processes

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Year-9-tectonic-processes-worksheet

The Earth

The Earth is one of nine planets in our solar system and formed 4.6 billion years ago. Over time the outside layer cooled to form solid rock however the centre remains very hot.

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Structure of the Earth

The Earth is made up of four distinct layers:

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The inner core is in the centre and is the hottest part of the Earth. It is solid and made up of iron and nickel with temperatures of up to 5,500°C. With its immense heat energy, the inner core is like the engine room of the Earth.
The outer core is the layer surrounding the inner core. It is a liquid layer, also made up of iron and nickel. It is still extremely hot, with temperatures similar to the inner core.
The mantle is the widest section of the Earth. It has a thickness of approximately 2,900 km. The mantle is made up of semi-molten rock called magma. In the upper parts of the mantle the rock is hard, but lower down the rock is soft and beginning to melt.
The crust is the outer layer of the earth. It is a thin layer between 0-60 km thick. The crust is the solid rock layer upon which we live.

Tectonic plates

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The Earths crust is broken into large slabs of rock called tectonic plates. There are seven major plates and twelve smaller ones. There are two different types of plates continental plates and oceanic plates.
Continental plates – they are less dense, cannot sink into the mantle and they form land.
Oceanic plates – they are dense, can sink into the mantle and be destroyed and they form the sea bed.

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Continental drift

The theory of continental drift was first suggested by the German meteorologist Alfred Wegener in 1912. Wegener contended that the relative positions of the continents are not rigidly fixed but are slowly moving—at a rate of about one yard per century. This idea laid the groundwork for the modern plate tectonics theory.

Heat rising and falling inside the mantle creates convection currents. The convection currents move the plates. Where convection currents diverge near the Earth’s crust, plates move apart. Where convection currents converge, plates move towards each other. The movement of the plates, and the activity inside the Earth, is called plate tectonics.

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Plate tectonics cause earthquakes and volcanoes. The point where two plates meet is called a plate boundary. Earthquakes and volcanoes are most likely to occur either on or near plate boundaries.

Plate boundaries

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Plate boundaries (margins) are the places where two or more tectonic plates meet (along the black lines in the diagram above).

There are four types of plate boundaries, namely: constructive boundary, destructive boundary, collision boundary and conservative boundary.

Click on the link in red.

Plate Tectonics

 

Constructive boundary:
Plates move apart
Lava erupts along this plate margin
New crust (land) is formed along these boundaries

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Destructive boundaries:
Oceanic and continental plates move together
Heavy oceanic crust is pushed down into the mantle
Oceanic crust is melted
Explosive volcanoes
Violent earthquakes
Most hazardous boundary

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Collision boundaries:
Continental plates move together
Plates buckle and form fold mountains
Violent earthquakes
Little to no volcanic activity

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Conservative boundaries:
Plates move in different directions
Plates get stuck and pressure builds up
Plate breaks along the fault line releasing the pressure
Massive earthquakes
No volcanoes

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Volcanoes

A Volcano is a mountain formed from eruptions of lava and ash.

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Volcanoes can be classified as active, dormant or extinct.

still active and erupt frequently
dormant (temporarily inactive but not fully extinct)
extinct (never likely to erupt again)

Volcanoes can also be described by their shape or type – shield or composite.

Shield volcano

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Shield volcanoes are usually found at constructive or tensional boundaries.
They are low, with gently sloping sides.
They are formed by eruptions of thin, runny lava.
Eruptions tend to be frequent but relatively gentle.

Composite volcanoes

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Composite volcanoes are made up of alternating layers of lava and ash (other volcanoes just consist of lava).
They are usually found at destructive or compressional boundaries.
The eruptions from these volcanoes may be a pyroclastic flow rather than a lava flow. A pyroclastic flow is a mixture of hot steam, ash, rock and dust.
A pyroclastic flow can roll down the sides of a volcano at very high speeds and with temperatures of over 400°C.


Effects of volcanic eruptions

Volcanic eruptions can have a devastating effect on people and the environment.
However, volcanoes can also have a positive impact on an area. These positive impacts can help to explain why people choose to live near volcanoes.

Negative effects

Many lives can be lost as a result of a volcanic eruption.
If the ash and mud from a volcanic eruption mix with rain water or melting snow, fast moving mudflows are created. These flows are called lahars.
Lava flows and lahars can destroy settlements and clear areas of woodland or agriculture.
Human and natural landscapes can be destroyed and changed forever.
Lahars a landslide of wet volcanic debris on the side of a volcano.

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Positive effects

The dramatic scenery created by volcanic eruptions attracts tourists. This brings income to an area.
The lava and ash deposited during an eruption breaks down to provide valuable nutrients for the soil. This creates very fertile soil which is good for agriculture
The high level of heat and activity inside the Earth, close to a volcano, can provide opportunities for generating geothermal energy.

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Viscosity

What do we mean by viscosity? Viscosity refers to the gooeyness” or resistance to flow

viscosity

Water has low viscosity (flows easily) while syrup and honey have greater viscosity.

The character of volcanic eruptions are largely controlled by the viscosity – “gooeyness” or resistance to flow – of the magma: Low viscosity fluids flow more easily than high viscosity fluids

  • Viscosity increases with increasing silica content due to silica chains
  • High viscosity lavas flow slowly and typically cover small areas. In contrast, low viscosity magmas flow more rapidly and form lava flows that cover thousands of square kilometres.
  • Low viscosity magmas allow gases to escape easily whereas gas pressures can build up in high viscosity magmas – resulting in violent eruptions (Blowing through a straw, it’s easier to get water to bubble than a milk shake)

Calderas

A collapse is triggered by the emptying of the magma chamber beneath the volcano, usually as the result of a large volcanic eruption. If enough magma is ejected, the emptied chamber is unable to support the weight of the volcano above it. A roughly circular fracture, develops around the edge of the chamber. The total area that collapses may be hundreds or thousands of square kilometres.

Case Studies

Case study – Montserrat

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Montserrat is located in the Caribbean, it is a volcanic island 12 miles long and 3 wide. Known as the ‘Emerald Isle’ Montserrat is largely undeveloped with a few towns and one main city – Plymouth.

Montserrat is also located on the boundary between the Caribbean and North American plates, this is a destructive plate boundary so the volcano that Montserrat is built around is of a composite nature.

The volcanic section of the island, known as Soufriere Hills erupted in 1995 after a dormancy period of 300 years.

In 1997 a major eruption devastated the southern part of the island and buried the capital, Plymouth. Agricultural land was destroyed, villages were flattened and 19 people were killed.

The crisis prompted more than half of the island’s population to leave; those who stayed were evacuated to the north. The restless volcano has prevented their return.

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2/3 of the island was covered in ash
50% of the population were evacuated to the north of the island to live in makeshift shelters
23 people died in 1997
Plymouth – the capital became a ghost town
Floods as valleys were blocked with ash
The airport and port were closed
Farmland was destroyed
Forest fires caused by pyroclastic flows
Many schools and hospitals were destroyed

Responses to the Eruption

£41 million was given in aid by the British Government. Money was given to individuals to help them move to other countries. Riots occurred as locals complained that the British were not doing enough to help the island.

A Risk assessment was done to help islanders understand which areas are at risk and reduce problems for the future.

Mount St Helens eruption

Using the information from the video (above) design your own case study. Use the following headings – What, when, where and why did it happen. Within your report you need to include the following – maps, photographs / images and diagrams.

Supervolcanoes

A supervolcano is a volcano on a massive scale. It is different from a volcano because:

  • it erupts at least 1,000 km3 of material (a large volcano erupts around 1 km3)
  • it forms a depression, called a caldera (a volcano forms a cone shape)
  • a supervolcano often has a ridge of higher land around it
  • a supervolcano erupts less frequently – eruptions are hundreds of thousands of years apart

A supervolcano is any volcano capable of producing a volcanic eruption with an ejecta mass greater than 1015 kg. Supervolcanoes can occur when magma in the mantle rises into the crust from a hotspot but is unable to break through the crust, and pressure builds in a large and growing magma pool until the crust is unable to contain the pressure (this is the case for the Yellowstone Caldera).

Yellowstone

yellowstone-caldera-supervolcano-diagram

Yellowstone is one example of a supervolcano. Three huge eruptions have happened in the last 3 million years. the last eruption was 630,000 years ago, and was 1,000 times bigger than the Mount St Helens eruption in 1980.

The large volume of material from the last Yellowstone eruption caused the ground to collapse, creating a depression called a caldera. The caldera is 55 km by 80 km wide. The next eruption is predicted to have catastrophic worldwide effects.

Yellowstone 5eed0ae88c27990a6c1d695fd1e3f505

The timebomb under Yellowstone: Experts warn of 90,000 immediate deaths and a ‘nuclear winter’ across the US if supervolcano erupts

Prep: To find out where Yellowstone National Park is and to discover the hidden dangers that lies beneath.
Task 1 – Produce a fact sheet about Yellowstone National Park. Include the following: 
a. continent, country and state

b. Nearest cities and the population

c. Physical features

d. Images and location map

Task 2 – Research ‘Old Faithful Geyser’ in the Park. What is it and how does it work?  Check out the two videos below to get you started. 

Task 3 – Google research the ‘Sulphur Caldron’ in Yellowstone. Why wouldn’t you take a dip there?

 

Earthquakes

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Earthquakes happen mainly in areas where plate boundaries meet. There are two key terms associated with earthquakes. – the focus and the epicentre. The focus is where the earthquake originates underground and the epicentre is where the earthquake is felt on the surface directly above the focus.

Seismic waves ripple out wards from the epicentre in all directions.

Impacts of earthquakes

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Disrupt Normal Life.
Affects a Large number of People.
Losses to Lives, Livelihoods, Property.
Loss of housing.
Damage to infrastructure
Disruption of transport and communication.
Disruption of marketing systems.
Breakdown of social order.
Loss of business.
Loss of industrial output.
Fire because gas pipes have been broken and catch fire
Tsunamis which can wipe out large coastal areas – high waves.
Disease due to fact that there is a lack of clean water.

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Recording earthquakes

The power of an earthquake is measured using a seismometer. A seismometer detects the vibrations caused by an earthquake. It plots these vibrations on a seismograph.

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The strength, or magnitude, of an earthquake is measured using the Richter scale. The Richter scale is numbered 0-10.

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year-9-tectonic-processes-indian-ocean-earthquake-and-tsunami

Case study – The Kobe Earthquake – an earthquake affecting a HIC

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Kobe is located in the south east of Japan, near a destructive plate margin. It is a megacity and has one of the largest container ports in the World. Although further from a plate margin than most of the cities in Japan, Kobe is still found on a fault line. The earthquake that hit Kobe during the winter of 1995 measured 6.9 on the Richter scale.

At this plate margin, the Pacific plate is being pushed under the Eurasian plate, stresses build up and when they are released the Earth shakes. This is known as an earthquake happening along a subduction zone. The focus was only 16km below the crust and this happened on the 17th Jan 1995 at 5.46am. 10 million people live in this area.

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Effects

The effects of this earthquake were catastrophic for an HIC. Despite some buildings having been made earthquake proof during recent years many of the older buildings simply toppled over or collapsed. A lot of the traditional wooden buildings survived the earthquake but burnt down in fires caused by broken gas and electricity lines. Other effects included
More than 5000 died in the quake
300,000 were made home less
More than 102,000 buildings were destroyed in Kobe, especially the older wooden buildings.
Estimated cost to rebuild the basics = £100 billion.
The worst affected area was the centre. This was because it was built on easily moving ground which LIQUIFIED, allowing building to collapse and sink.

The worst effected area was in the central part of Kobe including the main docks and port area. This area is built on soft and easily moved rocks, especially the port itself which is built on reclaimed ground. Here the ground actually liquefied and acted like thick soup, allowing buildings to topple sideways.

Emergency aid for the city needed to use damaged roads but many of them were destroyed during the earthquake.

Raised motorways collapsed during the shaking. Other roads were affected, limiting rescue attempts.

Many small roads were closed by fallen debris from buildings, or cracks and bumps caused by the ground moving.
The earthquake occurred in the morning when people were cooking breakfast, causing over 300 fires, which took over 2 days to put out.

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Responses to the quake

Water, electricity, gas, telephone services were fully working by July 1995
The railways were back in service by August 1995

A year after the earthquake, 80% of the port was working.

New laws were passed to make buildings and transport structures even more earthquake proof.

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More instruments were installed in the area to monitor earthquake movements.

Most new buildings and roads have, in the last 20 years, been designed to be earthquake proof, schools and factories have regular earthquake drills, etc. Despite this, many older buildings still collapsed or caught fire. This led to many blocked roads and massive problems of homelessness.

Telephones and other communication services were put out of action making communication slow and difficult.

Electricity and water supplies were badly damaged over large areas. This meant no power for heating, lights, cooking, etc. Clean, fresh water was in short supply until April 1995. The government and city authorities were criticised for being slow to rescue people and for refusing offers of help from other countries.

Many people had to sleep in cars or tents in cold winter conditions

Solutions

Preparation – A lot of the buildings in Kobe and Japan made after the 1960s are earthquake proof (necessary by law) with counterweights on the roofs and cross steel frames. Many of the damaged buildings in Kobe were built before this period and were made of wood, which caught fire. People are educated on earthquake preparation in Japan.
Prediction – Japan has the world’s most comprehensive prediction programme with thousands of seismometers and monitoring stations in Japan designed to give warning. Kobe hadn’t had an earthquake in 400years and had less prediction equipment than other areas of Japan.
Aid – The Japanese rejected international offers of aid and dealt with the earthquake itself. All of the homeless people were dealt with reasonably quickly and the city recovered thanks to government money.

Tsunami

the wave

 

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