tectonic hazards

Define a natural hazard.

A naturally occurring event that threatens life and property.

What are the four types of hazards and their definitions?

1. Tectonic Hazard (a hazard caused by movement or friction of the Earth’s tectonic plates, e.g. volcano or earthquake).

2. Atmospheric Hazard (caused by changes in climate, e.g. temperature and precipitation).

3. Geomorphic Hazard (processes on the Earth’s surface, e.g. avalanche)

4. Biological Hazard (involving living organisms, e.g. forest fires)

What physical factors affect hazard risk?

Frequency, magnitude, climate change, and land-use.

What human factors affect hazard risk?

Wealth, population growth, and urbanisation.

What is the theory of plate tectonics?

The theory that all Earth’s continents used to be connected in one ‘super-continent’.

What is a ‘plate’?

The divided sections of Earth’s lithosphere (outer layer) that move around the surface of the globe.

What is a ‘plate margin’?

Where the plates meet.

Where are volcanoes and earthquakes most commonly found and why?

Plate margins, because this is where the plates can interact and create areas that cause magma to rise to the surface.

What is the infamous ring on the pacific plate where many tectonic hazards occur?

The Ring of Fire

What are convection currents?

Circular movements in liquids and gases caused by temperature differences, where hotter & less dense material rises and cooler & denser material sinks.

How does magma rise?

Magma starts in the mantle, before getting heated by the core and rising to the crust. It cools and loses heat, before sinking.

What are fold mountains?

Mountain ranges formed when Earth's tectonic plates collide, causing the layers of rock to crumple and fold upwards.

What happens at a constructive margin?

• Hot magma rises due to convection currents.

• The plates move away from each other due to “ridge push”.

• Magma rises in-between and cools to form solid rock (most magma won’t reach the surface and become lava).

• Volcanoes formed are usually shield volcanoes.

What’s an example of a constructive margin?

Case study: Iceland 

• The Eurasian and North American plate meet to form ridges and several shield volcanoes.

What happens at a destructive margin?

• The oceanic crust subducts under the continental crust, forming a deep ocean trench, due to “slab pull”.

• This happens due to the different characteristics of the plates.

• This causes friction.

• The tip of the oceanic crust melts due to the heat in the mantle, forming new magma which rises up the vent.

• Pressure increases and it’ll explode violently.

• Earth’s continental crust can crumple and form fold mountains (e.g. the Andes.)

What’s an example of a destructive margin?

Case Study: Japan

• Four plates meet here (Eurasian/Pacific/Indo-Australian/Philippine) resulting in many active volcanoes.

What happens at a collision margin?

• Two continental crusts move towards each other due to convection currents.

• They collide and are forced upwards.

• Fold mountains and big earthquakes form.

What happens at a conservative margin?

• The oceanic and continental crust are moving parallel to each other due to convection currents.

• One is moving faster and friction causes them to get stuck.

• They remain stationary, pressure builds up, and eventually the rock fractures.

• Pressure is released as a highly destructive earthquake.

How does “ridge push” and “slab pull” explain plate tectonics?

“Ridge push” occurs as gravity pulls newly formed crust down and away. “Slab pull” is the force where a dense, sinking plate at a subduction zone pulls the rest of the plate behind it into the mantle.

What are some differences between continental and oceanic crust?

CONTINENTAL	OCEANIC
thinner	thicker
formed of basaltic rock	formed of granite
up to 3B years old	less than 200mill years old

What are the four ways of managing the risk of hazards?

Monitoring: Observing the hazardous site for signs of disaster, e.g. ground tremors or heat sensors. 

Prediction: Forecasting the likelihood of a disaster and identifying prone areas.

Protection: Reducing a hazard’s impacts.

Planning: Responding to the event, e.g. evacuation.

How could you manage the risks of a volcanic eruption?

Monitor: Tiltmeters to monitor ground deformation, heat sensors to detect changes in the temperature of the volcano’s surface.

Predict: Seismometers to show small ground tremors.

Plan: Evacuation, emergency shelters, education on preventing injury and loss of life.

Protect: Evacuation (hard to prevent a volcano’s impacts).

How could you manage the risks of an earthquake?

Monitor: Detection devices to measure radon gas in the soil and groundwater, seismometers to detect ground movements.

Predict: Time and location can be mapped to spot patterns, animals believed to act amiss before an impending eruption.

Plan: Fasten furniture down, emergency supplies prepared, emergency services.

Protect: Build reinforced/earthquake-resistant infrastructure - usually costly.

Define mitigate.

To reduce an event’s impact.

What tectonic hazard is believed to be harder to prevent, and why?

Volcanoes: Difficult to protect from it and reduce the flow of lava.

What is considered the most effective response to a volcanic eruption, and why?

Evacuation: We can accurately predict when it’ll erupt, so it’s easier to prepare and evacuate people.

Define primary effect and give an example.

Effects that happen at the time of the event e.g. ground shakes.

Define secondary effect and give an example.

Later effects due to the damage of the event e.g. loss of livelihood.

Define immediate response and give an example.

Action taken during the event to prevent loss of life e.g. evacuation.

Define long-term response and give an example.

Action taken over a long period of time to rebuild the area e.g. constrction of homes.

What are the characteristics of an earthquake?

Why may people continue to live in hazardous areas?

• Fertile soil creates opportunity for farming/agriculture which leads to a stable income.

• Tourism brings people to these dangerous sites.

• Cultural importance.

• Financial hardship.

• People refuse to believe the risks (apathy/denial).

Discuss an example of an LIC that has suffered an Earthquake.

Nepal - April 2015 Magnitude: 7.7

• 1/3 of the population was affected.

• Many historical landmarks destroyed.

• $5b USD in damage.

• Economy dropped due to loss of tourism at the capital.

• Avalanches and landslides triggered.

• International aid from UK, China, & India.

• £87m GBP raised in relief funds.

• Government introduced strict building regulations that have better shake resistance.

Discuss an example of an HIC that has suffered an Earthquake.

Chile - February 2010 Magnitude: 8.8

• 500 killed and 12,000 injured.

• $30b USD in damage.

• Triggered landslides damaged 1500km of roads.

• Tsunami triggered had little impact on Chile.

• 500 temporary shelters set up.

• Repairs on road made quickly.

• Chile were prepared, so little reliance on foreign aid.

• Recovery would take 4 years.

Did Nepal or Chile suffer worse? Why?

Nepal:

• Less money for emergency services, medics, and rebuilding of the country.

• Poor quality infrastructure means buildings collapse quicker.

• Slower recovery efforts and economy has plummeted.

• Not prepared, so much reliance on foreign aid.

• Repairs made slowly.

What is the difference between a hazard and an event?

A hazard has to threat a population.

Define Hazard Risk.

The probability that a hazard will affect a population.

What is the structure of the Earth?