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Flashcards in 3. Natural Hazards Deck (38)
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What is a natural event

Something happening in the physical environment, such as a storm, volcanic eruption or earthquake.


What is a hazard

An event which threatens the well-being of PEOPLE and their property


What is a natural hazard

A natural hazard is an extreme natural event that can cause loss of life, extreme damage to property and disrupt human activities.


Give 3 examples of a geological hazard

- earthquake
- tsunami
- volcanic eruption


Give 3 examples of a climatic hazard

- hurricane
- tornado
- blizzard


Give 3 examples of a biological hazard

- fires (grassland/forest)
- plague/ insect infestation
- diseases


Give 3 examples of a technological hazard

- nuclear explosion
- pollution
- accidental release of toxic chemicals


What is a natural disaster

A disaster is the realisation of a hazard.


What is a tropical cyclone

A tropical cyclone is a weather system of very low-pressure formed over tropical seas and involving strong winds and heavy rainfall (also known as a cyclone, hurricane or typhoon).


What is the Saffir-Simpson Hurricane Wind Scale (measurement)

The Saffir-Simpson Hurricane Wind Scale is a 1 to 5 rating based on a hurricane’s sustained wind speed. This scale estimates potential property damage.


What is the range in wind speed of the Saffir-Simpson Hurricane Wind Scale

74mph (category 1) - 157mph (category 5)


Where are tropical cyclones distributed

Between roughly 5-20° north/south of the equator where water is deep and warm


Where do we call a tropical cyclone a 'hurricane'

Atlantic and Northeast Pacific - hurricane


Where do we call a tropical cyclone a 'typhoon'

Northwest Pacific


Where do we call a tropical cyclone a 'cyclone'

South Pacific and Indian Ocean


Key characteristics of a tropical cyclone

- Humid, warm, unstable air, low pressure
- A constant supply of energy (the warm water)
- Warm water above 27*
- A circulatory motion of air and small changes in wind speed and direction


Is a tropical cyclone a weather system of low or high pressure

LOW PRESSURE (A low pressure system has lower pressure at its centre than the surrounding areas. Winds blow towards the low pressure, and the air rises in the atmosphere where they meet. As the air rises, the water vapour within it condenses, forming clouds and often precipitation.


Weather conditions when the hurricane approaches

- temp and pressure begin to fall
- (winds from the north-west)


Weather conditions for the first 'wall' of the storm

- pressure falls rapidly
- cumulonimbus clouds with thunder and torrential rain


Weather conditions in the eye of the hurricane

- period of calm, sun makes a brief appearance
- pressure very low


Weather conditions for the second 'wall' of the storm

- hurricane winds and torrential rain
- (south-east winds, temp drops, pressure rises)


Weather conditions towards the end of the hurricane

- pressure and temperature rise
- rain and wind decrease


What is the Coriolis force

- scientist's explanation for why a moving object (tropical cyclone) will veer towards the right in the Northern Hemisphere and the south in the Southern Hemisphere
- due to the earth's rotation on its axis (rotates faster at the equator than at poles)


What is wind shear

Wind shear is the change in speed or direction of wind over a relatively short distance or time period. Hurricanes need small changes in wind speed and direction, but if the wind shear force is too strong, then hurricanes may dissipate because the storm is pushed or spread over a larger area


Specify what is meant by 'unstable air pressure'

Where areas of high pressure and low pressure meet


State and explain 3 physical effects of a tropical cyclone

1. flooding - crop damage - food shortage - starvation
2. heavy rain causing freshwater flooding - spread of disease due to unhygienic conditions - drinking contaminated water - illness + death
3. strong winds - destroy infrastructure/ housing - homelessness, loss of income - social disorder/conflict


Give one short term impact of a tropical cyclone

Strong winds - destroy infrastructure/ housing - leaving people homeless


Give one long term impact of a tropical cyclone



What is a volcanic eruption

Volcanic eruptions happen when lava and gas are discharged from a volcanic vent.


What is lahar

lahar is a mudflow caused by water and debris mixing during a volcanic eruption. It is an Indonesian term that describes a mixture of water and rock fragments.
It makes a hot, muddy flow that usually flows down existing river valleys, collecting debris and causing severe destruction to property.


What is pyroclastic flow

A pyroclastic flow is a hot moving current of ash and gas. It is the most dangerous characteristic of a volcanic eruption.


What dangerous gasses are released after a volcanic eruption

- sulphur
- cyanide
- carbon dioxide


Why are ash clouds dangerous

- Ash causes damage by blanketing everything e.g. crops and roads
- Roofs of buildings often collapse under the weight of deposited ash


What is a destructive/convergent plate boundary

This occurs when oceanic and continental plates move together. The oceanic plate is forced under the lighter continental plate. Friction causes melting of the oceanic plate and may trigger earthquakes. Magma rises up through cracks and erupts onto the surface.


What is a constructive/divergent plate boundary

A constructive plate boundary occurs when plates move apart. Volcanoes are formed as magma wells up to fill the gap, and eventually new crust is formed.


What are hotspots

- Some volcanoes do not occur on plate boundaries, so they can be formed over hotspots.
- These are fixed points in the mantle that generate intense heat (in a mantle plume). Small, long lasting, exceptionally hot areas of magma exist under the Earth’s surface which in turn sustains long-lasting volcanic activity.
At areas where the pressure is greater in the mantle, magma erupts through the crust as when the plume reaches the crust it causes the crust to dome (and crack).
Volcanoes are created if the magma rises above the ocean surface.


What is a collision plate boundary

Collision zones form when two continental plates collide. Neither plate is forced under the other, and so both are forced up and form fold mountains.


What is a conservative plate boundary

A conservative plate boundary, sometimes called a transform plate margin, occurs where plates slide past each other in opposite directions, or in the same direction but at different speeds.

Friction is eventually overcome and the plates slip past in a sudden movement. The shockwaves created produce an earthquake.