The Challenge of Natural Hazards

How do Earthquakes occur?

Two plates against each other eventually getting stuck, then the pressure starts to build
The plates pressure gets too great, they jolt violently in opposite directions causing an earthquake
The center of the earthquake is called the focus, waves are released from the jolt, these are called seismic waves
The place where the seismic waves first hit the ground is called the epicenter. Buildings here will receive the most damage

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At constructive plate margins, the two tectonic plates move apart
Magma is injected between the two plates adding new materials to plates creating volcanoes at the surface. These volcanoes are not very dangerous or explosive. Small tremors are common. They are produced by the movement of rising magma and are more like small earthquakes than large earthquakes.

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At destructive subduction plate margins, the two tectonic plates move together.
The oceanic plate subducts beneath the continental plate since it is denser
Magma forms as the oceanic plate melt. The magma rises through the continental plate and erupts at the surfaces.
The volcanoes are large, explosive and dangerous. Earthquakes happen because of pressure between the continental and subducting oceanic plate. These earthquakes can be shallow or deep and are often very violent.

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At conservative plate margins, the two tectonic plates slide past each other.
There are no volcanoes at conservative plate margins, and no magma erupts from the surface. Sometimes the plates cannot move past each other and get stuck.
Pressure builds up until the plates give way. This produces large destructive earthquakes.

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The plate boundaries move away from each other
The space left between them allows the magma to spill out easily
The lava becomes runny because it has a low viscous level which slowly spills out
The lava slowly dries and layers over the previous layers of lava creating a wide base
This shield volcano will continue to grow over thousands of years

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The plate boundaries are moving towards each other
The viscous lava (meaning it is thick) has to burst through the plate margin and work its way up, some lava will dry which creates explosions of ash
The lava and ash will layer over each other, the volcano has a narrow base because the thick lava does not move fast.

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All air exerts a weight on the earth's surface. This is known as air pressure. We measure air pressure in millibars using a barometer. The weight air depends on whether air is cold or warm. Warm air is light so it rises. As it rises, the pressure at the surface decreases leading to low pressure. Cold air is dense (heavy) so it sinks. As it sinks, the pressure. High-pressure systems are called anticyclone; low-pressure systems are called depressions.

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The center of the storm is called the eye - it's up to 50km cross and caused by descending air
There is very high pressure, light winds, no clouds, no rain and a high temperature in the eye
The eye is surrounded by the eyewall, where there's spiraling rising air, very strong winds, storm clouds, torrential rain, and a low temperature
Towards the edges of the storm the wind speed falls, the clouds become smaller and more scattered, the rain becomes less intense and temperature increases.

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