Hazards and case studies

Volcanoes, earthquakes, tsunamis, hurricanes, wildfires, drought and famine, tornadoes

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  • Created on: 23-09-13 20:23
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Nicola Critten ­ AS Geography
Key locations
Volcanoes occur most frequently at plate boundaries.
Some volcanoes, however, like those that form the Hawaiian Islands, occur in the interior of plates at areas
called hot spots.
Volcanoes occur at the area known as the subduction zone. This is where one plate sub ducts, beneath
another. When the sub ducting plate reaches about 100 kilometres into the Earth's hot mantle, it triggers partial
melting and forms new magma. Some of the magma rises and erupts as volcanoes.
Shield Volcano
Constructive boundaries
They are low, with gently sloping sides.
Formed by eruptions of thin, runny lava.
Eruptions tend to be frequent but relatively gentle.
Composite Volcano
Destructive boundaries
Formed of alternating layers of lava and ash (other volcanoes just consist of lava).
The eruptions may be a pyroclastic flow rather than a lava flow. A pyroclastic flow is a mixture of hot steam,
ash, rock and dust.
A pyroclastic flow can roll down the sides of a volcano at very high speeds and with temperatures of over
How are they measured?
Volcanic Explosivity Index (EVI)
Can they be predicted?

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Nicola Critten ­ AS Geography
Most volcanoes provide various types of warnings before eruptions begin
Such as:
Anomalous heat flow or changes in the temperature and chemistry of the ground and spring waters.
People living near volcanoes may detect premonitory events before an eruption. Both the frequency of
occurrence and intensity of felt earthquakes commonly increase before eruptions begin.
Eruptions may be preceded by noticeable steaming and also by new or enlarged areas of hot ground.…read more

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Nicola Critten ­ AS Geography
The sulphur dioxide released led to a decrease in world temperatures.
Mitigation? In the days leading up to the eruption people were evacuated resulting in less
deaths than there potentially could have been.…read more

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Nicola Critten ­ AS Geography
Key Locations
Most earthquakes occur along the edge of the oceanic and continental plates. Earthquakes usually occur
where two plates are running into each other or sliding past each other.
Earthquakes can happen along ANY TYPE of plate boundary (usually conservative).
How do they occur?
Earthquakes occur when tension is released from inside the crust. Plates do not always move smoothly
alongside each other and sometimes get stuck. When this happens pressure builds up.…read more

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Nicola Critten ­ AS Geography
The time of year and climate will influence survival rates and the rate at which disease can spread.…read more

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Nicola Critten ­ AS Geography
Case Study: Kobe, Japan 1995 ­ MEDC
It occurred in a heavily populated urban area in Japan. It
measured 7.4 on the Richter scale.
5,000 killed
$100 billion damage
Buildings and bridges collapsed despite their earthquake proof design.
Buildings destroyed by fire when the gas mains fractured.
316,000 people left homeless and refugees moved into temporary housing.…read more

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Nicola Critten ­ AS Geography
What is a tsunami?
A tsunami is a huge wave, usually caused by volcanic or earthquake activity under the ocean, which can
eventually crash onto the shoreline. The effects on a community can be devastating.
When an earthquake, volcano or landslide happens on the ocean floor, water is displaced. This water forms
the start of the tsunami.…read more

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Nicola Critten ­ AS Geography
Hurricanes / Tropical Cyclones
(Known as typhoon in the Pacific Ocean)
Where do they occur?
Hurricanes are most common in the Pacific Ocean, as
they need warm water (27 degrees +) to form.
Hurricanes need four conditions to form:
Low air pressure
Warm temperatures
Moist ocean air
Tropical winds (near the equator)
Hurricanes form in the tropics, over warm ocean water (over 27ºC).…read more

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Nicola Critten ­ AS Geography
Case Study: Katrina, USA, 2005
Hurricane Katrina tracked over the Gulf of Mexico.
Storm surges reached over 6 metres in height and
there were 127 mph winds.
New Orleans was one of the worst affected areas
because it lies below sea level and is protected by
levees. These protect it from the Mississippi River
and Lake Ponchartrain. The levee defences were unable to cope with the strength of
Katrina, and water flooded into the city.…read more


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