Tectonic Hazards Flashcards
Layers of the Earth
Crust, mantle, inner core, outer core
The plate tectonics….
Are continually moving at 2-3cm per year. They float on top of the mantle.
How do the tectonic plates move? State
Because of convection currents in the mantle. Convention currents are hot molten rock (magma).
Explain how convection currents allow the plates to move? EXAM Q
Convection currents in the mantle are heated up due to the temperature in the Earth’s core. The convection currents are hot and this means they rise to the top. When they cool down they sink. This continues to happen and moves the tectonic plates
How do we know the tectonic plates moved?
East coast of South America and west coast of Africa fit like a jigsaw as they used to be one continent. Fossils are similar on both continents. land animals would have been unable to swim across an ocean were found on South America and Africa.
Where do volcanoes and earthquakes happen?
Along plate margins, where two or more tectonic plates meet each other.
Why do earthquakes and volcanoes form where they do?
Volcanoes are fed by hot molten rock from deep within the Earth. This rises to the top at plate margins. There is one exception - volcanoes can form at ‘hot spots’. This is when the tectonic plates are very thin and magma breaks through e.g Hawaii.
Constructive plate margins
- The plates are moving apart due to convection currents inside the Earth.
- As the plates move apart, magma rises from the mantle. The magma erupts to the surface of the Earth. Can be accompanied by Earthquakes.
- When the magma reaches the surface, it cools and solidifies to form a new crust of igneous rock. This process repeats over a long period of time.
- Eventually the new rock builds up to form a volcano. Found under the sea e.g Mid Atlantic Ridge
Destructive Plate Margin
- The plates are moving towards each other. This usually involves a continental plate and an oceanic plate.
- The oceanic plate is denser than the continental plate so, as they move together, the oceanic plate is forced underneath the continental plate.
- The point at which this happens is called the subduction zone. 4. As the oceanic plate is forced below the continental plate it melts to form magma and earthquakes are triggered.
- The magma collects to form a magma chamber.
- This magma then rises up through cracks in the continental crust. As pressure builds up, a volcanic eruption may occur.
An example of this is the Nazca Plate is sub-ducted under the South American Plate
Conservative plate boundaries
- At a conservative plate margin the tectonic plates slide past each other.
- Friction between the plates causes Earthquakes.
- Earthquakes happen along conservative margins as stresses gradually build up over many years.
- An example of this is the San Andreas Fault in California. 5. The faster moving Pacific Plate is sliding in the same direction as the as the slower moving North American Plate.
- There are NO VOLCANOES AT THIS MARGIN. This is because no magma rises to the surface.
Christchurch Earthquake - summary
HIC - New Zealand – 2011 -
The earthquake measured 6.3 on the Richter Scale. It struck New Zealand at 12:51 on 22 February 2011. The epicentre was 6 miles South East of Christchurch and the focus was very shallow at 3.1 miles. The earthquake occurred on a conservative plate margin where the Pacific Plate slid past the Australian Plate in the different direction.
Haiti Earthquake Summary
LIC - Haiti – 2010
- The earthquake was caused by the North American Plate sliding past the Caribbean Plate at a conservative plate margin.
- The North American Plate moved westwards, the Caribbean moved eastwards.
- The earthquake measures 7 on the Richter Scale with an epicentre 16 miles West of Port- au-Prince and a shallow focus of 5 miles.
- The earthquake struck at 16:53 (4:53pm) local time on Tuesday 12 January 2010.
Primary effects
The initial impact of a natural event on people and property, caused directly by it, for instance the ground buildings collapsing following an earthquake. Includes deaths.
Secondary effects
The after-effects that occur as indirect impacts of a natural event, sometimes on a longer timescale, for example disease spreading.
Primary Effects of Christchurch Earthquake
- 181 killed, 2000 injured.
- 50% + of Central City buildings severely damaged inc the cathedral which lost its spire.
- Hundreds of km of water and sewage pipes were damaged.
- Liquefaction (where the ground gets saturated and loses strength) caused damage to roads and buildings.
- 20 football fields worth of the country’s longest glacier was broken off, creating a large iceberg.
