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)
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
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
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
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
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
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
8
Q
Temperate Climate
A
• Moderate summers and winters
• Low pressure belt at about
60° N/S caused by rising air
• Rainfall is frequent
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
10
Q
Polar Climate
A
• Temperatures are low all year round
11
Q
Tropical Climate
A
• Temperatures are hot
• Usually near the equator, low pressure belt caused by rising air
• Rainfall is high
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
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
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
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
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
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
18
Q
What are tropical storms?
A
- Intense low pressure weather systems with heavy rain and strong winds that spiral around the centre
19
Q
What are tropical storms also known as?
A
- Hurricanes
- Typhoons
- Cyclones
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
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
22
Q
How do tropical storms get stronger?
A
- Due to energy from the warm water, so wind speeds increase
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
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
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
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
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
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
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
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
