GCSE AQA Geography Section A: Tectonic Hazards

What are tectonic plates?

Rigid segment of the Earth's crust which 'floats' across heavier, semi-molten rock

What is a plate margin/boundary?

Where two tectonic plates meet (where natural hazards form)

Tectonic plates are made of 2 types of crusts...

continental crust
- old (1500 million+ y.o.), less dense, cannot sink, cannot be renewed/destroyed, thicker than oceanic (30-50km)

oceanic crust
- new (less then 200 y.o.), denser, can sink, can be renewed/destroyed, thinner (5-10km)

What are destructive margins?

- two plates are moving towards each other; an oceanic plate meets a continental plate, the denser oceanic plate subducts into the mantle and destroyed creating gas-rich magma. volcanoes and ocean trenches occur here.
- two continental plates meet, ground folds upwards creating fold mountains

What are constructive margins?

Where two plates are moving away from each other; magma rises from the mantle to fill the gap and then cools, creating new crust

What are conservative margins?

Plates are moving sideways past each other or are moving in the same direction but at different speeds.

What hazards are associated with destructive (o>c) plate boundaries?

earthquakes from friction of subduction

volcanoes as final product

What hazards are associated with convergent (c>c) plate boundaries?

earthquakes from collison

fold mountains from final product

What hazards are associated with constructive plate boundaries?

earthquakes through breaking through crust

volcanoes as final products

What hazards are associated with conservative plate boundaries?

earthquakes through friction

What is an earthquake?

The shaking that results from the movement of rock beneath Earth's surface.

What is the focus in earthquakes?

The position in the Earth from where the Earthquake originated

What is the epicentre in earthquakes?

The point of the Earth's surface directly above the focus

What are the 2 scales which measures earthquakes and what they measure?

-Richter Scale measures energy released
-Mercalli Scale measures visible impacts

What is the definition of a volcano?

A volcano is a rupture in the surface of the Earth that allows molten lava, ash and gas to escape.

What measures volcanoes?

Volcanic Explosivity Index

What plate boundaries are volcanoes found?

volcanoes are found at constructive and destructive plate boundaries

What are the distinctive features of a volcano?

Main vent, secondary vent, crater, magma chamber and the explosive material

What do volcanoes produce?

ash, lava, volcanic bombs, pyroclastic flows or lahars

What are positive effects of volcanoes?

- geothermal energy

- ash (to fertilise soil)

- tourism

What are negative effects of volcanoes?

- danger

- damage to property

- difficulty for businesses to operate

- damage to habitats/landscapes

What is a lahar?

a destructive volcanic landslide or mudlfow, consisting of a mixture of volcanic debris, mud, rock and water

What are composite volcanoes?

tall, cone-shaped mountains with layers of lava alternating with layers of ash; having acid lava and violent eruptions within long period of erupting

What are shield volcanoes?

Quiet eruptions gradually build up a gently sloping mountain with basic lava and shorter periods between eruptions

Where do you find composite volcanoes?

You find composite volcanoes on destructive plate margins

Where do you find shield volcanoes?

You find shield volcanoes on constructive plate boundaries

How do you monitor changes to a shape of a volcano?

Tiltmeters and GPS measures the change of shape of a volcano

What are the warning signs of an eruption

escaping gas and rising temperatures

Why do people live by volcanoes?

- volcanic land and ash provides fertile land increasing crop yields for farmers

- tourism > money > benefits economy

- geothermal energy -> cheaper electricity for locals

- minerals in lava make money (diamonds)

How many people live on or close to volcanoes?

500 million (1/14th of population)

What are the risks of living near or on a volcano?

- gas pollution
- uncertain living conditions/evacuation
- losing jobs/ no livelihood
- no insurance for damage
- high vulnerability
- homelessness

What are the management strategies for reducing the risk of tectonic hazards?

Monitoring- scientific equipment detects warning signs of events

Prediction- using historical evidence and monitoring, scientists can predict when and where tectonic hazards may happen

Protecting- designing buildings that will withstand tectonic hazards

Planning- identifying and avoiding places most at risk

How are volcanoes monitored?

- measuring gas detection released as magma rises
- remote sensing detects heat and changes to shape of volcano by satellites
- ground deformation shows the changes to the shape of the volcano- measured using laser beams
- geographical measurements detect changes in gravity as magma rises to the surface

How are earthquakes monitored?

Hard to monitor as they're below ground but changes in water pressure, ground deformation and minor tremors prior to an earthquake

How are earthquakes predicted?

- Seismic Gap Theory
- detecting gases Thoron and Boron shows the plates are reacting

How are volcanoes predicted?

- based on scientific monitoring

What protection is there from earthquakes?

EARTHQUAKE PROOF BUILDINGS:
- reinforced concrete and steel walls reduce movement
- open evacuation areas
- shock absorbers to absorb ground shaking
- automatic shutters prevents broken glass falling
- triangular shaped buildings

what protection is there from volcanoes?

- earth embankments or explosives to divert lava flow
(done on Mount Etna in Italy)

How can you plan for tectonic hazards?

- hazard maps
- training people on earthquake drills or education through TV/RADIO
- emergency kits (first aid, blankets, water, tinned food)