Tectonic Hazards

Plate tectonics theory

The earth is divided into four main layers :

The crust : Its the outer layer. Its divided into tectonic plates that float on the mantle. Its thickness varies and is made up of two types of crust. (Oceanic and continental crust)

Inner core - About 1400km in diameter, a solid and dense layer composed of iron and nickel with temperatures of about 5500°C

Outer core - About 2100km thick, a semi-molten metal layer with temperatures between about 5000-5500°C

Mantle - About 2900km thick, a semi-molten layer which is less dense than the outer core 

Oceanic crust - Thinner and more dense

Continental crust - thicker and less dense

Plates move because of convection currents in the mantle and they meet at plate boundaries.

Three types of plate margins :

• Destructive margins - Where two plates move towards each other. Its where the oceanic plate meets the continental plate and the denser oceanic plate is subducted and destroyed creating gas rich magma. Volcanoes and ocean trenches also occur here. When two continental plates meet the ground is folded upwards creating fold mountains.

• Constructive margins - When two plates move away from each other. Magma rises from the mantle to fill the gap and cools creating new crust.

• Conservative plate margins - When two plates move sideways past each other or in the same direction but at different speeds. Crust isnt created or destroyed.

Global distribution of Volcanoes

Volcanoes form at destructive and constructive plate margins

In destructive plate margins, the denser oceanic crust moves down into the mantle where it melts. A pool of magma then forms and rises into the cracks in the crust called vents. The magma then erupts forming volcanoes.

In constructive plate margins, the magma rises up into the gap created by the plates moving apart forming a volcano

Earthquakes form at all 3 plate margins

Destructive - tension builds when one plate gets stuck as it tries moving past the other

Constructive - tension builds along the cracks when the plates try moving away from each other

Conservative - tension builds when the plates that are grinding past eachother get stuck

Chile and Nepal case study

Reasons why people choose to live in areas at risk of tectonic hazards

• They may have always lived there - leaving means that that they are leaving jobs and family

• In wealthier countries, effective monitoring and evacuation plans can minimise risks

• The minerals from volcanic ash can make volcanic soil very fertile attracting farmers

• Volcanoes are tourist attractions, so lots of people live nearby to work in tourist industries

Management strategies

Management reduces the risk of tectonic hazard. Management strategies reduce the number of people injured, killed, left homeless or unemployed.

Monitoring

Earthquakes - ibrahima and lasers monitor the earths movements, and can be used in early warning systems to give a small but vital amount of warning before a large earthquake occurs.

Volcanoes - scientists can monitor the tell tale signs that come before an eruption like escaping gas and changes in the shape of a volcano.

Prediction

Earthquakes - cannot be reliably predicted, but scientists can forecast where they might occur by movements of tectonic plates

Volcanoes - can be predicted if scientists monitor volcanoes closely.

Protection

Earthquakes - new buildings can use reinforced concrete that absorb the earthquakes energy. Existing builidings can be strengthened with steel frames so that they dont collapse.

Volcanoes - builidngs can be strengthened so that they are less likely to collapse under the weight of the ash

Planning

• Future developments can avoid high risk areas

• Governments can plan evacuation routes to get people home quickly and safely