Geography Natural Hazards Revision Cards

all you need to know for your exam in small easy to revise from bits.

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  • Created on: 08-06-12 12:01

Structure of the Earth

1. The Inner Core

It is in the centre and is the hottest part of the Earth (around 5,500 degrees celcius). It is solid and made up of iron and nickel.

2. The Outer Core

It is the layer surrounding the inner core. It liquid and also made up of iron and nickel. It is extremely hot (simmilar teperatures to the inner core).

3. The Mantle

It is made up of semi-molten rock called magma. It has a diameter of approximately 2,900km. Towards the surface of the Earth the rock is hard but towards the middle of the Earth the rock is beginning to melt.

4. The Crust

The outer layer of the Earth on which we live. It is between 0 and 60 km thick. It is made up of rock.

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Types Of Plates

Oceanic Plate

A plate that caries water, it is denser than a continental plate.

Continental Plate

A plate that carries land, it is less dense than an oceanic plate.

Convection Currents

Radioactive decay in the core of the Earth causes hot circular convection currents. These currents cause the plates to move.

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Plate Boundaries


Plates move away from each other, allowing room for magma from the mantle to rise up and solidify and form new crust made of igneous rock. Tend to be found under the sea like the Mid Atlantic Ridge and form volcanoes and can trigger earthquakes.


A continental plate and an oceanic plate move towards each other, when they collide the oceanic plate goes underneath the continental as it is denser and begins to melt in the subduction zone. Earthquakes are common here.


Two plates move side by side in opposite directions or in the same direction but at different speeds. Earthquakes are very common here but volcanoes never occur on a continental plate boundary.

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What is an Earthquake?

An earthquake is the vibration of the Earth's crust due to tension being released from inside the crust when plates get stuck against each other. They can occur on all three different types of plate boundaries.


Step 1:

Destructive margins- Tension builds up when one plate gets stuck as it's moving down past the other into the mantle.

Constructive margins- Tension builds along cracks within the plates as they move away from each other.

Conservative margins- Tension builds up when plates that are grinding past each other get stuck.

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Earthquakes Continued...

Step 2

The plates eventually jerk past each other sending out shock waves (vibrations, this is the earthquake).

Step 3

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.

Step 4

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

Earthquakes can be Measured

The Richter scale- Measures the magnitude of an earthquake using a seismometer

The Mercalli scale- Measures the effects of an earthquake (scale of 1-12).

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Volcanoes are found at destructive and constructive plate margins.


Step 1

Magma rises through cracks in the Earth's crust and pressure builds up inside the Earth

Step 2

When this pressure is released, magma explodes to the surface causing a volcanic eruption.

Step 3

The lava from the eruption cools to form new crust and over time, after several eruptions the rock builds up and a volcano forms.

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Tropical Storms


1. Several thunder storms drift over seas over 27 degrees celcius.

2. Warm air from the sea and warm air from the storms combine and begin to rise.

3. More warm air rises and, because of the Earth's spin, begins to move in a spiral. It cools and condenses as it rises to form clouds.

4. The air rises faster and cooler air is sucked downwards. Wind speed increases.

5. Tropical storms move towards land, picking up warm, moist air along the way making it stronger. More cool air is drawn into the eye of the storm

How are they Measured?

Tropical storms are measured using the Saffir Simpson Scale, which takes into account wind speed and effects.

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What is a Wildfire?

A wildfire is a large, uncontrolled fire that moves quickly. Itmay be caused naturally or by humans.

Where do wildfires Occur?

They occur along the Tropic of Cancer and the Tropic of Capricorn. The cannot occur along the equator as there are rainforests that are too wet.

What helps Wildfires to Spread?

Fires need fuel, heat and oxygen to spread. Wind provides oxygen. vegetation and houses provide fuel and weather provides heat. The intensity of the fire depends of these three things.

Ladder Fuels

Tall grasses help set shrubs on fire and then taller trees. This is an effective way of a fire setting large things on fire quickly.

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Santa-ana Winds

(For case study of California)

Santa-ana winds blow from the desert, as they cross the Sierra Nevada mountains they accelerate and then warm as they descend and compress the the coastal plain (California).

These hot and dry winds dry out vegetation increasing the amount of fuel avaliable to fuel fires. The gusty winds swirling through crayons and valleys also fan fires with oxygen.

It is important to remember, however, that these winds do not start firse they just make existing fires spread quickly.

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El Nino

(For the case study of Australia)

The rain that usually comes from South America and falls on the tropical rainforests of Australia get blown over and fall on South Americas's desert land instead.

This means that Australia's rainforests are dry and perfect conditions for a wildfire to take hold.

The clouds and rainstorms also fall on South America, causing flooding and even dryer conditions compared to usual in Australia.

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