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ZZ Geog 1 > global hazards > Flashcards

global hazards Flashcards

1
Q

What are winds?

A
  • Large scale movements of air caused by difference in pressure
  • Differences in pressure are caused by differences in temperatures (between the equator and the poles)
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2
Q

What happens at the Hadley Cell?

A
  • At the equator the Sun warms the Earth
  • Transfers heat to the air above causing it to rise
  • Creates a low pressure belt with rising air, clouds and rain
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3
Q

What happens at the Ferrell Cell?

A
  • As the air rises it cools and moves out to 30° N/S of the equator
  • The cool air sinks creating a high pressure belt with cloudless skies and low rainfall
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4
Q

What happens at the Polar Cell?

A
  • The cool air reaches the ground surface and moves as surface winds (either back to the equator or towards the poles)
  • At 60° N/S, the warmer surface winds meet colder air from the poles
  • The warmer air is more dense than the cold air so it rises creating low pressure
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5
Q

What are trade winds?

A
  • Surface winds blowing towards the equator are called trade winds
  • Blow from the SE in the southern hemisphere and NE from the northern hemisphere
  • At the equator TW meet and are heated by the sun causing them to rise and form clouds
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6
Q

What are westerlies?

A
  • Surface winds, blowing towards the poles are called westerlies
  • The blow from the NW in the southern hemisphere and from the SW in the northern hemisphere
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7
Q

What happens to the air at the Poles?

A
  • Some of the air moves back towards the equator and the rest move towards the poles
  • At the poles, the cool air sinks, creating high-pressure
  • The high pressure air is drawn back towards the equator as surface winds
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8
Q

Temperate Climate

A

• Moderate summers and winters
• Low pressure belt at about
60° N/S caused by rising air
• Rainfall is frequent

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9
Q

Arid Climate

A
  • Temperatures are hot or warm.
  • High pressure belt at about 30° N/S caused by sinking air
  • Rainfall is very low all or most of the year
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10
Q

Polar Climate

A

• Temperatures are low all year round

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11
Q

Tropical Climate

A

• Temperatures are hot
• Usually near the equator, low pressure belt caused by rising air
• Rainfall is high

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12
Q

What causes extremes in temperature?

A
  • The equator receives the most energy from the Sun
  • The poles receive the least
  • Heat drives atmospheric circulation as warm air from the equator moves to the poles
  • 30° N/S - high pressure causing sinking air meaning there are few clouds
  • Little to block the Sun’s energy therefore temps can be high
  • Temps of polar regions are very low
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13
Q

What causes extremes in precipitation?

A
  • Precipitation occurs when warm, wet air rises and cools, causing water vapour to condense
  • Low pressure belt causes air to rise, precipitation is frequent
    e.g. Rainforests (the Amazon)
  • High pressure belt causes air to sink, precipitation is low
    e.g. Deserts (the Sahara)
  • Exact location of pressure belts varies slightly over time
  • Places that normally have moderate weather can experience dry/wet weather depending on high/low pressure belt
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14
Q

What causes extremes in winds?

A

*Global atmospheric circulation causes winds (air moving from areas of high to low pressure)
* Winds are weak in high and low pressure belts
* Winds are strong between pressure belts
* When the difference in pressure between high and low pressure areas is large, winds can be extremely strong
e.g. North Coast of Australia

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15
Q

Australia vs UK - Temperature

A
  • Australia is warmer than the UK - has hotter summers and milder winters
  • Australia: avg max temp 33°C, can reach over 40°C (extremely hot)
  • London: avg max temp 23°C, temp over 30°C considered extremely hot
  • Australian summers are about 10°C warmer than UK
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16
Q

Australia vs UK - Precipitation

A
  • Australia has much lower precipitation than the UK
  • Australia: avg annual rainfall is 465mm
  • Extremely wet years: over 550mm
  • Extremely dry years: less than 360mm
  • UK, avg annual rainfall is over 1150mm
  • Wet years: over 1210mm
  • Dry years: less than 950mm
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17
Q

Australia vs UK - Wind

A
  • Australia has stronger extreme winds than the UK
  • Australia affected by tropical cyclones with winds over 118km/h
  • Strongest wind recorded over 400km/h on Barrow Island in 1996
  • UK, gales are rare (winds of over 62km/h)
  • Strongest wind recorded over 220km/h, in Scotland in 1989
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18
Q

What are tropical storms?

A
  • Intense low pressure weather systems with heavy rain and strong winds that spiral around the centre
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19
Q

What are tropical storms also known as?

A
  • Hurricanes
  • Typhoons
  • Cyclones
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20
Q

When do tropical storms develop?

A
  • When the sea temp is 27°C or higher
  • Warm ocean temp means there is lots of warm, moist air to cause extreme precipitation
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21
Q

What causes a tropical storm?

A
  • When warm air rises and cools (condensation) huge amounts of energy is released
  • Makes the storms powerful
  • Rising air creates an area of low pressure, increasing surface winds
  • Earth’s rotation (Coriolis effect) deflects paths of the winds, causing storm to spin
  • Earth spins faster at the Equator because it’s wider
  • Winds speeds increase towards the centre of the storm, around the eyewall
  • Inside the eye of storm, wind speeds decrease rapidly, low pressure
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22
Q

How do tropical storms get stronger?

A
  • Due to energy from the warm water, so wind speeds increase
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23
Q

How do tropical storms cause extreme winds?

A
  • Strong winds are caused by a big pressure difference to the surrounding area
  • Centre of the storm has very low pressure
  • Wind speeds of more than 250 km/h
  • Strong enough to damage or destroy buildings and plants
  • Causes loose objects to be picked up and transported
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24
Q

How do tropical storms cause extreme precipitation ?

A
  • Large amounts of warm moist air sucked towards centre of storm due to difference in pressure
  • As this happens, the air rises, cools and condenses, causing rain
  • Causes flooding and mudslides
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25
Q

Describe the distribution of tropical storms

A
  • Occur between 5° and 30° N/S of the equator (any further water isn’t warm enough)
  • Majority occur in the northern hemisphere in late summer and autumn (when sea temps are the highest)
  • At least 500km away from the Equator where the Coriolis effect is strong enough to make the weather system spin
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26
Q

Describe the frequency of tropical storms

A
  • Number varies each year
  • In the Atlantic, number has increased since 1984, however no overall trend for past 30 years
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27
Q

What are the normal conditions in the Pacific Ocean?

A
  • Trade winds blow West
  • Wind high in the atmosphere blows East
  • Warm surface water, strong currents
  • Western Pacific (Australia) has low pressure
  • Air rises, causing rain and thunderstorms
  • Eastern Pacific (South America) has high pressure
  • Air sinks, causing clear skies and dry weather
  • Cold upwelling
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28
Q

What happens during La Nina?

A
  • When normal conditions become more extreme
  • Trade winds blows west more strongly
  • More cold upwelling in Eastern Pacific
  • Causes more heavy rainfall and floods in the Western Pacific
  • Causes less rainfall and droughts in the Eastern Pacific
  • Occurs every 2-7 years
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29
Q

What happens during El Nino?

A
  • Trade winds weaken or reverse direction
  • Trade winds blow East
  • Winds high in atmosphere blows West
  • Trade winds blow West
  • Wind high in the atmosphere blows East
  • Warm surface water, currents are weaker or in the opposite direction to normal
  • Western Pacific (Australia) has high pressure
  • Air sinks, causing clear skies and droughts
  • Eastern Pacific (South America) has low pressure
  • Air rises, causing rain, thunderstorms and floods
  • Cold upwelling blocked
  • Occur every 3-4 years and lasts for 9-12 months
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30
Q

What is drought?

A
  • A long period when rainfall is below average
31
Q

What happens during a drought?

A
  • Water supplies becomes depleted as people keep using them but they aren’t replenished by rainfall
  • Droughts are accompanied by high temperatures which increase the rate of evaporation so water supplies are depleted faster
32
Q

What causes a drought?

A
  • Changes in atmospheric circulation means it doesn’t rain as much in an area for months or years
    e.g. Australia
  • Can also make the annual rains fail
    e.g. monsoon rains don’t come when they normally do
  • Caused when high pressure weather systems (anticyclones) block deperessions (weather systems that cause rain)
    e.g. UK
33
Q

Describe the distribution of droughts

A
  • Areas most at risk are central and Southern Africa, the Middle East, Australia, eastern South American and parts of North America
  • Locations affected by droughts vary over time
34
Q

Describe the frequency of droughts

A
  • Varied from year to year but overall has not changed much since 1950
  • Some scientists have suggested that droughts might become more frequent and more severe due to climate change
35
Q

Describe the core

A
  • Inner core is a ball of solid iron and nickel
  • Outer core is liquid
36
Q

Describe the mantle

A
  • Semi-molten rock that moves slowly
37
Q

Describe the crust

A
  • About 10-70km thick
  • Divided into slabs called tectonic plates that float on the mantle
38
Q

Describe the two types crust

A
  • Continental - less dense, thicker
  • Oceanic - more dense, thinner
39
Q

How do convection currents work?

A
  • Convection currents are circular movements that cause tectonic plates to move
  • Lower parts of the mantle are sometimes hotter than the upper parts
  • When these lower parts heat up they become less dense and slowly rise
  • As they move towards the top, they cool down, become more dense, then slowly sink
40
Q

What are plate boundaries?
Name examples

A
  • Where tectonic plate meets
41
Q

What happens at a destructive plate boundary?

A
  • Two plates move towards each other
  • The oceanic plate is more dense and is forced down into the mantle (subduction)
  • It rubs and causes frictions which melts the plate and creates magma
  • Often creates volcanoes and ocean trenches
    e.g. the Pacific plate being forced under the Eurasian plate on the east coast of Japan
42
Q

What happens at a collision plate boundary?

A
  • Two plates move towards each other
  • They are both continental plates (same density)
  • Plates are folded and forced upwards
  • Ground buckles and reshapes under pressure creating fold mountains
    e.g. the Eurasian and Indian plate to form the Himalayas
43
Q

What happens at a constructive plate boundary?

A
  • Two plates move away from each other
  • Magma rises from the mantle and erupts from fissures and faults
  • Fills the gap and cools, creating new crust
    e.g. the Eurasian plate and the NA plate in the Mid-Atlantic Ridge
44
Q

What happens at a conservative plate boundary?

A
  • Two plates are moving sideways
  • Either moving past each other in opposite direction or same direction, different speeds
  • Rough edges snag and stick like Velcro causing friction and stress to build until one plate jolts forward
  • Crust isn’t created or destroyed
    e.g. the Pacific plate and the NA plate on the west coast of the USA
45
Q

How do destructive plate boundaries cause earthquakes?

A
  • Tension builds up when one plate gets stuck as it’s moving down past the other into the mantel
46
Q

How do collision plate boundaries cause earthquakes?

A
  • Tension builds as the plates are pushed together
47
Q

How do constructive plate boundaries cause earthquakes?

A
  • Tension builds along cracks within the plates as they move away from each other
48
Q

How do conservative plate boundaries cause earthquakes?

A
  • Tension builds up when plates that are grinding past each other get stuck
49
Q

What happens during an earthquake?

A
  • Tension builds (four plates)
  • The plates eventually jerk past each other sending out shock waves (vibrations)
  • Shock waves spread out from the focus
  • Near the focus, the waves are stronger and cause more damage
50
Q

What is the focus of an earthquake?

A
  • The point in the earth where the earthquake starts
  • Can be at the Earth’s surface or anywhere up to 700km below the surface
51
Q

What is the epicentre of an earthquake?

A
  • The point on the Earth’s surface straight above the focus
52
Q

How are earthquakes measured?

A
  • Using the moment magnitude scale
  • Measures the energy released by an earthquake
  • Or the Mercalli scale
  • Measures the effect/ intensity of impacts
  • Richter scale (no longer used) and measures energy released
53
Q

What are shallow-focus earthquakes?

A
  • Caused by tectonic plates moving at or near the surface
  • Have a focus between 0km and 70km below the Earth’s surface
54
Q

What are deep-focus earthquakes?

A
  • Caused by crust that has previously been subducted into the mantle
  • Moves towards the Earth’s centre and heats up or decomposes
  • Have a focus between 70km and 700km below the Earth’s surface
55
Q

How does depth affect an earthquake?

A
  • The deeper the earthquake the less damage
  • Have to travel through more rock to reach the surface, which reduces their power when they reach the surface
56
Q

What are the two types of effects of an earthquake?

A
  • Primary effects: occur instantly and as a direct result of the hazard
  • Secondary effects: a consequence of something else happening
57
Q

Give an example of a primary effect

A
  • Ground shaking
  • How strongly it shakes depends on
  • the strength of the earthquake
  • how deep the focus is
  • what the ground is made of (softer rocks shake more easily)
  • The longer the ground shakes, the stronger the damage
58
Q

Give examples of a secondary effect

A
  • Tsunamis: when the ground jolts under the sea, it propels water forwards to create a wave
  • Landslides/ avalanches: slopes become weaker due to violent shaking and develop faults and give way
  • Liquefaction: shockwaves cause deeper ground water to rise to the surface, and particles to shake together to become fluid
59
Q

How are volcanoes formed at destructive plate boundaries?

A
  • Oceanic plate moves into the mantle (as it’s less dense), where it is melted and destroyed
  • A pool of magma forms and rises through cracks in the crust called vents
  • The magma erupts onto the surface forming a volcano
60
Q

How are volcanoes formed at constructive plate boundaries?

A
  • The magma rises up into the gap created by the plates moving apart, forming a volcano
61
Q

What happens when a volcano erupts?

A
  • It emits lava and gases
  • Some emit lots of ash which can cover land, block out the sun and form pyroclastic flows (super-heated currents of gas, ash and rock)
62
Q

What are hotspots?

A
  • Volcanoes that are found away from plate boundaries
  • It’s a bit of the Earth’s crust that is hotter than normal
63
Q

How do hotspots occur?

A
  • A plume of hot magma from the mantle moves towards the surface
  • Creates an unusually large flow of heat from the mantle to the crust
  • Magma can break through the crust and reach the surface, causing an eruption and a volcano forms
  • Remain stationary over time, but the crust moves above them
  • Creates chains of volcanic islands
    e.g. Hawaii in the middle of the pacific plate
64
Q

How are composite volcanoes formed?

A
  • Occur at destructive plate boundaries
  • Subducted oceanic crust contains lots of water
  • Can cause the subducted crust to erupt
  • Eruptions start with ashy explosions that deposit a layer of ash
  • Then a layer of thick, sticky lava erupts
  • Can’t flow far forming a steep sided cone
    e.g. Mount Fuji, Japan
65
Q

How are shield volcanoes formed?

A
  • Occur at hotspots or constructive plate boundaries
  • Not very explosive only made p of lava
  • Lava is runny and flows quickly
  • Spreads over a wide area, forming a low, gentle-sided volcano
    e.g. Mauna Loa, Hawaii
66
Q

How can we “predict” earthquakes?

A
  • Radon gas emissions
  • Animal behaviour
  • Historic trends
  • Electromagnetism
67
Q

What are are early warning systems?

A
  • Networks of seismometers and lasers can be used to monitor earth movements in areas at risk of earthquakes
  • Can give a small warning before a large earthquake occurs
68
Q

What do early warning systems do?

A
  • Communicate warnings quickly and automatically to people and control systems when shaking is detected
  • Uses the internet, SMS networks and sirens
69
Q

Why are early warning systems useful?

A
  • People can get under cover before the shaking starts
  • People doing delicate or dangerous jobs can stop what they are doing and make the situation safe
  • Utilities like gas can be shut off to prevent leaks and fires
  • Trains can start slowing down to make derailments due to damaged track less likely
70
Q

How do scientists predict when an volacano will erupt?

A
  • Remotely operated seismometers, lasers and other senses can detect indications that an eruption is likely
  • Tiny earthquakes
  • Escaping gas
  • Changes in the shape of the volcano (e.g. bulges in the land where magma has built up under it)
71
Q

How do building designs reduce the impact of an earthquake?

A
  • Designed to withstand earthquakes
    e.g. using materials like reinforced concrete or building special foundations that absorb and earthquake’s energy
  • Existing buildings and bridges strengthened
    e.g. wrapping pillars in steel frames
  • Pipe lines designed to flex and not break, helps prevent death and damage to property caused by flooding and fires
72
Q

How can human activities make droughts worse?

A
  • Excessive irrigation
  • Dam building
  • Over farming and intensive farming
  • Deforestation - reduces transpiration; reduces soils ability to hold water
73
Q

What is the intertropical convergence zone?

A
  • A low pressure belt which enriches the globe
  • Where trade winds from NE and SE meet
  • Earth is tilted causing ICTZ to migrate between the tropics
  • Winds and pressure are shifted annually from N to S
  • Where two trade winds meet at the ITCZ: heavy precipitation as dry air and moist air combined
  • Some years ICTZ might not move as far to reach driest areas = drought

ZZ Geog 1 (4 decks)

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