Tectonic hazards

1.) The core of the Earth is a ball of solid (inner) and liquid (outer) iron and nickel.

2.) Around the core is the mantle.

     - It moves very slowly.

     - Semi-molten rock.

3.) The outer layer of the Earth is the crust.

4.) The crust is divided into slabs called tectonic plates which float on the mantle.  There are two types of crust:

Continental crust.

• Thick.
• Less dense.

Oceanic crust.

• Thinner.
• More dense.

5.) The plates move because of convection currents (cycle of heating, rising, sinking, cooling) in the mantle underneath the crust.

6.) The places where plates meet are called plate margins/ boundaries.

- Earthquakes and volcanoes are most likely to occur on plate boundaries.

- Some earthquakes do not occur at plate boundaries. They may be caused by human activity:

• Underground mining.
• Oil extraction.

- Volcanoes also form at hot spots, where the crust is thin and magma is able to break through to the surface. 

Eg, the Hawaiian Islands in the Pacific Ocean.

1.) Destructive - where two plates are moving towards each other.

E.g, West coast of South America.

• Where an oceanic plate meets a continental plate.
• Denser oceanic plate is forced down into the mantle and destroyed.
• Often creates volcanoes and ocean trenches. 

Fold mountains:

• Where two continental plates meet there is no subduction.
• The two plates collide and the crust becomes crumpled and uplifed.
• Collision forms fold mountains -e.g, Himalayas.
• This causes earthquakes. 
• There are no volcanoes at these collision margins because there is no magma.

Constructive plate boundaries - where two plate boundaries are moving away from each other.

E.g, along the Mid-Atlantic ridge.

- Magma (molten rock) rises from the mantle to fill the gap and cools, creating new crust.

- Forms volcanoes.

Conservative plate boundaries - where two plates are moving sideways past each other or are moving in the same direction but at different speeds.

- Friction between the plates causes earthquakes.

- Earthquakes happen along conservative plate boundaries as stresses gradually build up over many years. 

- They can be destructive as they are close to the Earth's surface. 

- These are released suddenly when the plates slip and shift. 

- There are no volcanoes becuase there is no magma.

E.g, San Andreas Fault in California. 

- Found at destructive and constructive plate boundaries.

• Destructive

1.) At destructive plate boundaries, the oceanic plate goes under the continental plate because its       more dense. 

2.) The oceanic plate moves down into the mantle, where it is melted and destroyed.

3.) A pool of magma forms.

4.) The magma rises through cracks in the crust.

5.) The magma erupts onto the surface (lava), forming a volcano.

• Constructive 

1.) The magma rises up into the gap created by the plates moving apart.

2.) Forms a volcano.

3.) Some volcanoes also form over parts of the mantle that are really hot (hotspots). E.g, Hawaii.

4.) When a volcano errupts, it emits lava and gases. Some volcanoes emit lots of ash.

Ash can:

- Cover land.

- Block out the sun.

- Form pyroclastic flows. 

- Earthquakes are caused by the tension that builds up at destructive, constructive and conservative plate boundaries.

• Destructive - tension builds up when one plate gets stuck as it's moving down past the other into the mantle.
• Constructive - tension builds up along cracks within the plates as they move away from each other.
• Conservative - tension builds up when plates that are grinding past each other get stuck.

- Plates eventually jerk past each other, sending out shock waves (vibrations.) 

- These vibrations are the earthquakes. 

- The shock waves spread out from the focus - the point in the Earth where the earthquake starts. Near the focus the waves are stronger and cause more damage. 

- The epicentre is the point on the Earth's surface straight above the focus.

Earthquakes are measured using the magnitude scale - measures the amount of energy released by an earthquake (magnitude.) 

The Effects of Earthquakes

• Primary ---> the immediate impacts of the ground shaking.
• Secondary --> what happens later on as a result of the primary effects. 

Primary effects:

• Buildings and bridges collapse.
• Homes are destroyed.
• People are injured or killed by collapsed buildings and falling debris.
• Electricity cables, gas and water pipes and communciations networks are damaged, cutting off supplies.

Secondary effects:

• Earthquakes can trigger landslides and tsuamis: these can destroy more buildings and cause more injuries/deaths.
• Leaking gas can be ignited, starting fires.
• People are left homeless and could die, e.g, from cold.
• There is a shortage of clean water and a lack of proper sanitation - spread of disease. 
• Due to blocked/destryoyed roads, aid and emergency cannot get through and trade is difficult.
• Businesses are damaged/destroyed, causing unemployment and lost income, tourits put off visiting the area.
• Repairs and reconstruction can be very expensive - can weaken a country's economy.

Immediate respones --> Action taken to prevent further loss of life or to prevent further damage to property.

Long-Term responses --> Action taken after a period of time after the incident.

Immediate responses 

• Rescue people trapped by collapsed buildings and treating injured people.
• Recover dead bodies to prevent spread of disease.
• Put out fires.
• Set up temporary shelters for people whose homes have been damaged/destroyed.
• Provide temporary supplies of water, food, electricity, gas and communication systems if regular supplies have been damaged.
• Foreign governments or charities may send aid workers, supplies, equipment or financial donations to the areas effected.
• Tech companies may set up disaster response tools, allowing damage to be recorded and people to confirm their safety. 

Long term responses 

• Re-house people who lost their homes.
• Repair/rebuild damaged buildings, roads, railways and bridges.
• Reconnect broken electricity, water, gas and communications connections.
• If necessary, improve building regulations so that buildings are more resistant to damage from earthquakes.
• Set up initiatives to help economic recovery. E.g, by promoting tourism.

Primary effects

• Buildings and roads are destroyed by lava flows and pyroclastic flows. Buildings may also collapse from ash.
• People and animals are injured/killed by pyroclastic flows, lava flows and falling rocks. 
• Crops are damaged.
• Water supplies are contaminated when ash falls on them.
• People, animals and plants are suffocated by volcanic gases.

Secondary effects

• Mudflows (lahars) form when volcanic material mixes with water. E.g, from heavy rainfall or snow melt. Mudflows and landslides cause more destruction, death and injury. 
• Flooding can be caused by hot rock, ash and gas melting ice and snow on the volcano. 
• Rock and ash can clog up rivers and dams, making flooding worse. 
• Transport networks are blocked/destroyed - aid and emergency vehicles cannot get through and trade is difficult.
• People are left homeless. Damaged/destroyed businesses causes unemployment and loss of income.
• Tourism can be disrupted straight after an eruption.
• Ash makes fields more fertile once it is broken down.
• Recovering after an eruption can take a long time and be very expensive, weakening a country's economy.

The effects of earthquakes and the responses to them are different in different parts of the world.

HICs generally have:

• Less deaths.
• Less injuries.
• Less people made homeless.
• Less residents need to be relocated. 
• Less infrastructure damage.
• More money from the government to pay for repairs.

Reasons why people live in areas at risk from tectonic hazards:

• They have always lived there - moving away means leaving friends and family.
• They're employed in the area - if people move away they would have to find new jobs.
• They're confident of support from their government after an earthquake/volcanic erruption. E.g, help to rebuild homes.
• Some people think volcanic erruptions/earthquakes won't happen again in the area.
• The soil around volcanoes is fertile - it is full of minerals from volcanic ash and lava. This makes it good for growing crops which attracts farmers.
• Volanoes are tourist attractions - lots of people live around volcanoes to work in the tourist industry. 

Management can reduce the effects of tectonic hazards: 

Monitoring:

• Networks of seismometers and laser monitor earth movements.
• Can be used in early warning systems to give a small but vital amount of warning before a large earthquake occurs. 
• Scientists can monitor signs that come before a volcanic eruption. 
• Things such as tiny earthquakes, escaping gas and changes in the shape of the volcano mean an erruption is likely.

Prediction

• Earthquakes cannot be reliably predicted but by monitoring the movement of tectonic plates scientists can forecast which areas should be prepared for one to occur.

Protection

• Buildings can be designed to withstand earthquakes.
• Existing buildings and bridges can be strengthened so they are less likely to collapse under the weight of falling ash or due to shaking from an earthquake.
• Automatic shut-off switches can be fitted to turn off gas and electricity supplies to prevent fires if an earthquake is detected by a monitoring system. 

Planning

• Future developments can be planned to avoid the areas most at risk from tectonic hazards.
• Emergency services can train and prepare for disasters. E.g, practicing rescuing people. This will reduce the number of people killed.
• People can be educated so they know what to do if an earthquake or erruption happens.
• Governments plan evacuation routes to get people out of dangerous areas quickly and safetly in case of an earthquake or volcanic eruption. This reduces the number of people killed or injured by things like fires, pyroclastic flows or mudflows.
• Emergency supplies can be stockpiled. If a natural hazard is predicted, the stockpiles can be moved close to areas likely to be affected.

Volcanoes 

• Seismic waves - using seismometers which produce seismometers 
• Monitoring gas emissions - as magma rises into magma chambers, gases escape . One of the main gases is Sulphur Dioxide, and if its quanitity in escaping volcanic gas increases, this can signal the start of a volcano.
• Ground deformation - The movement of magma within the crust can deform the ground above. The swelling of the volcano signals that magma has collected near the surface. 
• Satellite images and remote sensing - the use of satellites to detect things above the Earth's surface which is useful for monitoring changes in volcanoes at the surface. Heat or thermal activity can be monitored to check for upwelling magma, escaping Sulphur Dioxide and deformation in the ground by checking before and after images.

Earthquakes

• Seismometers - seismometers and using foreshocks by monitoring seismic waves can give warnings.
• Animal behaviour - animals react to an earthquake before the event.
• Laser beams - used to detect plate movement by directing the beam across the fault line.