Tectonic Hazards

The Earth has 4 main layers

  • Core
  • Mantle
  • Outer Core
  • Inner Core

Each layer has different characteristics. Study this diagram.

 

 

The heat from the core creates convection currents in the mantle. Semi-molten rock expands, becomes less dense and rises. As the mantle rock spreads near the crust it pulls or pushes the plates of the crust in different directions. The mantle rock cools, contracts, becomes more dense and sinks and completes the cycle.

These convection currents move the tectonic plates. This is the theory of plate tectonics. Tectonic hazards are caused by movements in the crust.

 

 

 

There are are two types of crust: oceanic and continental. Oceanic crust is found under the oceans. It is made of basalt: a heavy rock and is  7-10km thick. Continental crust makes up the land. It is made of granite and is up to 70km thick.

 

 

Most earthquakes and volcanoes occur on plate boundaries. They are typically found forming long lines or chains. They often occur along coastlines. They are most commonly found around the Pacific Ocean, in Asia, North America, South America and Oceania.

 

There are four types of plate boundary:

  • Constructive or divergent
  • Destructive or convergent ocean to land
  • Collision or convergent land to land
  • Conservative or transform

1.Constructive or divergent plate boundaries spread apart.

Two ­­­oceanic plates are moving apart, due to the convection currents beneath. As a gap is created between the plates new rock (magma) rises up to the surface from the mantle. This creates a chain of volcanoes, often underwater. This movement also causes earthquakes. This type of boundary is found in the centre of the Atlantic Ocean, forming an ocean ridge.

 

 

2.Desctructive or convergent ocean to land plate boundaries push together.

An ocean plate is pushed towards another plate by convection currents. The denser and heavier oceanic crust is pushed underneath another piece of crust, often the lighter and thicker continental crust. This is called subduction. As it is pushed down it creates a deep ocean trench. As it is pushed into the mantle it is heated and the plate melts to form magma creating volcanoes. The movement also causes earthquakes. This type of boundary occurs around the Pacific Ocean and is called the Ring of Fire.

 

3.Collision or convergent land to land plate boundaries push together.

Light and thick continental crust pushes into another piece of continental crust, due to convection currents. No crust is pushed down (subducted) at this boundary. Instead the crust and sediments fold up to create mountains called fold mountains. This movement creates earthquakes but no volcanoes. This type of boundary occurs between India and the rest of Asia creating the Himalaya Mountains.

 

4.Conservative or transform plate boundaries slide past each other.

Due to convection currents two plates (either oceanic or continental crust) slide past each other. They move in different directions or in the same direction at different speeds. Friction causes them to stick together until the pressure builds and they suddenly move. This releases seismic energy and creates earthquakes but not volcanoes. This type of boundary is found in California, USA along the San Andreas fault.

 

Volcanoes

Volcanoes erupt like a bottle of fizzy drink. The gas pressure builds in the magma chamber. This creates a weakness in the crust until a vent forms. The gas escapes very quickly carrying magma out through the crater. Outside the volcano this liquid rock is called lava. The explosion may also blast ash into the atmosphere. Runny lava at a divergent boundary creates a shield volcano with gently sloping sides. Sticky lava at a destructive boundary creates a steep sided cone volcano.

 

Earthquakes

Earthquakes occur where plates are rubbing together. The rough edges create friction. This prevents movement along the fault. The convection current increases the pressure until the friction cannot hold any longer. The plates move with a jerk. This creates seismic energy which spreads out from the focus – the point underground where the earthquake begins. It is felt strongest at the epicentre – the point on the surface above the focus. Earthquakes are measured on the Richter Scale with a seismometer.

 

 

CASE STUDY

Both Nepal and Japan are countries in Asia. They are both on the Eurasian Plate. Nepal is on a collision plate boundary between the Eurasian Plate and the Indo-Australian Plate. Japan is on a destructive plate boundary between the Eurasian Plate and Pacific Plate.

The effects of an earthquake in these two places are different. The table below compares the effects of an earthquake in a HIC (Hokkaido, Japan) and a LIC (Nepal).

 

A primary effect is damage done by the shaking of the earthquake, for example buildings collapsing. A secondary effect is caused indirectly by the earthquake, for example diseases spread due to the lack of clean water.

 

The table below shows the contrasting effects of a similar sized earthquake on two different countries:

Hokkaido earthquake, Japan Nepal earthquake
26th Sept 2003 4.50am
Magnitude 8.3		 25th April 2015 11.56am
Magnitude 7.8
Population density 336 people per km2
GDP (wealth) per person
US $38 000		 Population density 191 people per km2
GDP (wealth) per person
US $700
Deaths 0
Injuries 849
Damage $1.9 billion
1500 buildings damaged with 141 destroyed.
The earthquake caused a small tsunami 4m high.
Several bridges were damaged – one sank 12cm.
The ceiling collapsed in Kushiro airport affecting flights.
Several harbours were damaged and fishing and exports were affected for several weeks.		 Deaths 9000
Injuries 23 000
Damage $5 billion
300 000 homes damaged plus 600 000 destroyed
Half the country’s schools were destroyed affected the education of thousands of children.
Cholera spreads as a result of a lack of clean water and sanitation.
Avalanches on Mt Everest killed 22 climbers.
Landslides blocked roads affecting the rescue operation and the delivery of aid.
Many ancient temples destroyed.
Tourists may stay away resulting in fewer jobs and nearly US $1billion lost to the economy.

Nepal and Japan showed differing responses to the earthquakes. An immediate response is vital and happens straight away. A long term response may help prepare for the next earthquake so may happen later.

Nepal Earthquake Hokkaido Earthquake
Roads blocked so ask neighbouring countries for helicopters to distribute aid to isolated valleys Continue with the training drills on the 1st September each year so that people know how to respond to an earthquake
Request search and rescue teams from other countries to help find people trapped in the rubble Make sure every home has a survival kit that contains a radio, food, first aid kit, clothes and a torch.
Accept supplies of tents, food, water and medicine from countries around the world. Follow emergency plan and send in trained teams to assist with the clean-up operation
Set up relief camps for people who have lost their homes and all their possessions. Check how well the buildings and bridges stood up to the earthquake so lessons can be learned for the future
Ask for loans from the World Bank to help rebuild the infrastructure damaged in the earthquake Invest in scientists and equipment to try to predict when the next earthquake or tsunami might occur
Start a “Build Back Better” programme so the new homes are now built to withstand an earthquake

People live in areas at risk from tectonic activity for different reasons.

People live by volcanoes because…

  1. The ash creates fertile soil and this means agriculture is prosperous. For example, rice grows in fields around Mt Pinatubo in the Philippines and lemons grow on the slopes of Mt Etna in Sicily (Italy).
  2. Geothermal power can be used. The hot magma near the surface heats water for homes and businesses or creates steam for generating electricity. Geotherma power is used in Iceland and New Zealand.
  3. Minerals can be mined. Tectonic processes concentrate minerals in volcanic areas. Sulpher can be collected from craters in Indonesia. Copper, silver and gold can be mined in the volcanic Andes Mountains in South America.
  4. Tourism creates jobs. People travel to see volcanic features such as lava flows in Hawaii (USA), Roman ruins in Pompeii (Italy) and geysers in Yellowstone National Park (USA).

People live in earthquake zones because…

  1. They may feel safe because they live in a HIC and buildings are designed to be earthquake proof. For example homes in USA and Japan are well built and emergency teams are trained and prepared.
  2. They may live in a LIC and cannot afford to move. In Haiti many people are too poor to move away from the danger.
  3. They may consider that the jobs and lifestyles on offer are worth the risk of an earthquake occuring. For example, California is prone to earthquakes but millions live there.

Predicting when tectonic hazards may occur

You can predict when an earthquake may occur using…

  1. The time since the last one. Earthquakes seem to occur in patterns so this may give a clue to when the next one may occur.
  2. Lasers to measure tiny movements in the crust. This may show pressure is building up in a fault and this could be a warning for an earthquake.
  3. Snakes. Supposedly animals can sense if an earthquake is imminent.

You can predict when a volcano may occur using…

  1. Gas measurements. This show is the gas pressure is increasing in the magma chamber. This could be a warning sign before an eruption.
  2. Temperature measurements. Increasing temperatures may show magma rising inside the volcano and allow you to give a warning.
  3. Shape measurements. This shows if the sides of the volcano are bulging. This could be a warning sign of gas pressure rising inside.

Planning and protection to reduce the risks of tectonic hazards

To plan ahead before an earthquake you can…

  1. Have training drills. In Japan on 1st September every year than practice how to respond to an earthquake.
  2. Educate people. In New Zealand pupils know to ‘drop, cover, hold’ in an earthquake.
  3. Use survival kits. In Japan most homes have a survival kit to help in the aftermath of an earthquake.

Buildings can be designed to protect people form earthquake danger.

In HICs like USA buildings can use base isolation. This is when ball bearings are used to separate the building from the ground. The ground can shake but the buidings stays still. Also water tanks are used on the roofs of sky scrapers. These act as a counter-balance to reduce the sway.

 

 

 

In LICs like Peru simple appropriate technology can be used. Geomesh can be wrapped around adobe (mud brick) homes. This reinforces the structure, preventing its collapse.

 

 

 

 

 

 

You can plan ahead before a volcanic eruption by…

  1. Educating people how to behave in an ash cloud. They should stay indoors and wear a mask or damp cloth over their face.
  2. Warning people. Warning signs can tell people if an eruption is likely. In some cases exclusions zones may be needed to keep people away from the dangers of a pyroclastic flow.

You can protect people by trying to stop lava flows and mudflows.

You can stop or deflect a lava flow using an earth ditch or bank. You could also try spraying the lava with water to cool it until it solidifies.

 

 

 

 

You can also construct channels to divert mudflows – called lahars – away from people. Barriers can also be installed to trap the largest boulders causing damage.