Global Hazards Theory

Question 1

Define natural hazard

Answer 1

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

Question 2

Define low/high air pressure

Answer 2

Low air pressure belts have warm, rising air.
High air pressure belts have cool, falling air.

Question 3

Define winds

Answer 3

Winds are large scale movements of air from areas of high pressure to areas of low pressure.

Question 4

Outline the global atmospheric circulation system

Answer 4

There are 3 types of global atmospheric circulation cells: Hadley, Ferrell, Polar (getting further from the equator).
At the equator the Sun warms the air so it rises, creating a low pressure belt, and cools and moves out.
At 30° cool air sinks, creating a high pressure belt and trade winds and westerlies.
At 60° warm surface winds meet cold winds from the poles and so rise, creating a low pressure belt.
At the poles cool air sinks, creating a high pressure belt and cold surface winds.

Question 5

Define trade winds

Answer 5

Trade winds are surface winds blowing towards the equator in the Hadley cells (from SE or NE). At the equator they are heated by the Sun, rising and forming clouds.

Question 6

Define westerlies

Answer 6

Westerlies are surface winds blowing towards the poles in the Ferrell cells (from NW or SW).

Question 7

Define prevailing winds

Question 8

Outline climate zones

Answer 8

Polar climates (outside 66°) have low temperatures year round.
Temperate climates (outside 30°) have moderate summers and winters and frequent rainfall caused by the 60° low pressure belt.
Arid climates (near 30°) are hot with very low rainfall for all or most of the year caused by the 30° high pressure belt.
Tropical climates (near the equator) are hot all the time and have high rainfall caused by the low pressure at the equator.

Question 9

Define albedo effect

Question 10

How does global atmospheric circulation lead to extreme weather?

Answer 10

Extreme winds occur between opposite pressure belts, especially when the difference is large (eg north coast of Australia).
Extreme temperatures occur in high pressure zones with few clouds - cold at in polar regions and hot at 30°.
Extreme precipitation occurs at pressure belts - low at high pressure and high at low pressure.

Question 11

Define tropical storm (aka hurricane, typhoon, cyclone)

Answer 11

A tropical storm is an intense low pressure weather system with heavy rain and strong winds that spiral around the centre.

Question 12

Describe formation of tropical storms

Answer 12

Tropical storms develop when the sea temperature is 27°C or higher and so there is lots of warm, moist air to cause extreme precipitation.
The warm air rises, creating a low pressure zone, and so surface winds are increased.
Earth’s rotation deflects the path of the winds, causing the spin.
Condensation and the warm water supply energy so wind speeds increase and the storm gets stronger.

Question 13

Describe the distribution of tropical storms

Answer 13

Tropical storms mostly occur between 5 and 30° where the water is warm enough.
The majority occur in the Northern Hemisphere, over the Pacific, in late Summer or Autumn when sea temperatures are highest.

Question 14

Describe the frequency of tropical storms

Answer 14

The annual number of tropical storms varies with no overall trend over the last 130 years.

Question 15

Define El Niño

Answer 15

El Niño events occur every 3-4 years on average, lasting for 9-12 months, weakening or reversing the normal conditions in the Pacific.

Question 16

Define La Niña

Answer 16

La Niña events occur every 2-7 years, strengthening the normal conditions over the Pacific.

Question 17

Outline normal conditions in the Pacific

Answer 17

Normally, there is low pressure over the western Pacific and high pressure over the east and so the trade winds blow west.
Cold water rises in the east so surface water is warm enough with strong currents following the trade winds.

Question 18

Define drought

Answer 18

A drought is a long period of below average rainfall.

Question 19

Define depression

Answer 19

A depression is a weather system that can cause rain.

Question 20

Define anticyclone

Answer 20

An anticyclone in a high pressure weather system that can block depressions to cause drought.

Question 21

Describe the distribution of drought

Answer 21

Areas most at risk from drought are central and southern Africa, the Middle East, Australia and eastern South America.
Since 1950, there has been more drought in Africa, Asia and the Mediterranean and less in the Americas and Russia.

Question 22

Describe the frequency of drought

Answer 22

Frequency of drought has fluctuated but not changed overall since 1950.
Some scientists suggest droughts may become more frequent and more severe due to climate change.

Question 23

Define inner/outer core

Answer 23

The core is at the centre of the Earth. The inner core is a ball of solid iron and nickel. The outer core is liquid.

Question 24

Define upper/lower mantle

Answer 24

The mantle is a layer of semi-molten rock around the core, moving very slowly. The lower parts are sometimes hotter than the upper parts.

Question 25

Define crust

Answer 25

The crust is the outer layer of the Earth, between 10-70km thick.

Question 26

Define lithosphere

Question 27

Define tectonic plate

Answer 27

Tectonic plates are slabs into which the crust is divided that float on the mantle.

Question 28

Define convection currents

Answer 28

Convection currents are circular movements of parts of the mantle (hotter lower parts become less dense and rise, and vice versa) that cause tectonic plates to move.

Question 29

Define oceanic crust

Answer 29

Oceanic crust is thinner and more dense than continental crust.

Question 30

Define continental crust

Answer 30

Continental crust is thicker and less dense than oceanic crust.

Question 31

Define plate margin

Answer 31

A plate margin is a place where tectonic plates meet.

Question 32

Describe destructive plate margins

Answer 32

Destructive plate margins are where an oceanic plate and a continental plate are moving towards each other, creating a subduction zone.

Question 33

Describe subduction zones

Answer 33

At subductions zones, an oceanic plate is forced down into the mantle and destroyed beneath a (less dense) continental plate, creating volcanoes and ocean trenches.

Question 34

Define fold mountains

Answer 34

Fold mountains are formed as plates are folded and forced upwards at collision plate margins.

Question 35

Describe collision plate margins

Answer 35

Collision plate margins are where two continental plates are moving towards each other, creating fold mountains.

Question 36

Describe constructive plate margins

Answer 36

Constructive plate margins are where two plates are moving away from each other. Magma rises and cools to create new crust.

Question 37

Describe conservative plate margins

Answer 37

Conservative plate margins are where two plates are moving sideways past each other at different velocities. Crust is neither created nor destroyed.

Question 38

Define hot spot

Answer 38

Hot spots are bits of the Earth's crust that are unusually hot due to a plume of hot magma from the mantle moving towards the surface, which can break through the crust and erupt to form a volcano. Hot spots remain stationary, but the crust moves above them, which can create chains of volcanic islands.

Question 39

Define focus

Answer 39

The focus is the point in the Earth where tension built at a plate margin is released, from which seismic waves spread out.

Question 40

Define shallow focus

Answer 40

A shallow focus is between 0 - 70km below the Earth's surface, resulting from tectonic plate movement.

Question 41

Define deep focus

Answer 41

A deep focus is between 70 - 700km below the Earth's surface, resulting from previously subducted crust heating up or decomposing.

Question 42

Define epicentre

Answer 42

The epicentre is the point on the Earth's surface directly above the focus.

Question 43

Define seismic waves

Answer 43

Seismic waves are the shock waves (vibrations) released from the focus, stronger closer to the focus. They are the earthquake itself - they cause the damage.

Question 44

Define Richter Scale

Answer 44

The Richter scale is an outdated measure of the energy released by an earthquake.

Question 45

Define moment magnitude scale

Answer 45

The moment magnitude scale is the currently adopted measure of the energy released by an earthquake.

Question 46

Define Mercalli Scale

Answer 46

The Mercalli scale is a measure of the effects of an earthquake.

Question 47

Define seismograph

Question 48

Define lava

Answer 48

Lava is magma above the Earth's surface.

Question 49

Define composite volcanos

Answer 49

Composite volcanoes occur at destructive plate margins, where the much water in subducted oceanic crust can cause it to erupt. Eruptions begin with ashy explosions that deposit a layer of ash, then acid lava is erupted, forming a steep-sided volcano.

Question 50

Define acid lava

Answer 50

Acid lava, erupted from composite volcanoes, is thick and sticky, so can't flow far.

Question 51

Define shield volcano

Answer 51

Shield volcanoes occur at hotspots or constructive plate margins. Eruptions are not very explosive and are made up only of basic lava, forming a low, gentle-sided volcano.

Question 52

Define basic lava

Answer 52

Basic lava, erupted from shield volcanoes, flows quickly and spreads over a wide area.

Question 53

Define magma chamber

Answer 53

A magma chamber is a pool of magma formed at a subduction zone as the oceanic plate is melted and destroyed.

Question 54

Define vents

Answer 54

Vents are cracks in the crust at subduction zones through which magma from the magma chamber rises to form a composite volcano.

Question 55

Define tephra

Answer 55

Tephra is any and all fragmental material released from a volcano in an eruption.

Question 56

Outline volcanic eruptions

Answer 56

Volcanic eruptions release lava and gases. Some also emit lots of ash, which can cover land, block out the Sun and form pyroclastic flows.

Question 57

Define pyroclastic flows

Answer 57

Pyroclastic flows are super-heated currents of gas, ash and rock.