Global Hazards Theory

Question 1

Define natural hazard

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 troposphere

Question 6

Define trade winds

Answer 6

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 7

Define westerlies

Answer 7

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

Question 8

Define prevailing winds

Question 9

Define rain shadow

Question 10

Outline climate zones

Answer 10

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 11

Define albedo effect

Question 12

How does global atmospheric circulation lead to extreme weather?

Answer 12

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 13

Define tropical storm (aka hurricane, typhoon, cyclone)

Answer 13

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

Question 14

Describe formation of tropical storms

Answer 14

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 15

Describe the distribution of tropical storms

Answer 15

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 16

Describe the frequency of tropical storms

Answer 16

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

Question 17

Define El Niño

Answer 17

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 18

Define La Niña

Answer 18

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

Question 19

Outline normal conditions in the Pacific

Answer 19

Normally, there is low presser 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 20

Define drought

Answer 20

A drought is a long period of below average rainfall.

Question 21

Define depression

Answer 21

A depression is a weather system that can cause rain.

Question 22

Define anticyclone

Answer 22

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

Question 23

Describe the distribution of drought

Answer 23

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 24

Describe the frequency of drought

Answer 24

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 25

Define inner/outer core

Answer 25

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 26

Define upper/lower mantle

Answer 26

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 27

Define crust

Answer 27

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

Question 28

Define lithosphere

Question 29

Define tectonic plate

Answer 29

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

Question 30

Define convection currents

Answer 30

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 31

Define oceanic crust

Answer 31

Oceanic crust is thinner and more dense than continental crust.

Question 32

Define continental crust

Answer 32

Continental crust is thicker and less dense than oceanic crust.

Question 33

Define plate margin

Answer 33

A plate margin is a place where tectonic plates meet.

Question 34

Describe destructive plate margins

Answer 34

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

Question 35

Describe subduction zones

Answer 35

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 36

Define fold mountains

Answer 36

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

Question 37

Describe collision plate margins

Answer 37

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

Question 38

Describe constructive plate margins

Answer 38

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

Question 39

Describe conservative plate margins

Answer 39

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

Question 40

Define hot spot

Answer 40

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 41

Define focus

Answer 41

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

Question 42

Define shallow focus

Answer 42

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

Question 43

Define deep focus

Answer 43

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

Question 44

Define epicentre

Answer 44

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

Question 45

Define seismic waves

Answer 45

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 46

Define Richter Scale

Answer 46

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

Question 47

Define moment magnitude scale

Answer 47

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

Question 48

Define Mercalli Scale

Answer 48

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

Question 49

Define seismograph

Question 50

Define lava

Answer 50

Lava is magma above the Earth’s surface.

Question 51

Define composite volcanos

Answer 51

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 52

Define acid lava

Answer 52

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

Question 53

Define shield volcano

Answer 53

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 54

Define basic lava

Answer 54

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

Question 55

Define magma chamber

Answer 55

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

Question 56

Define vents

Answer 56

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

Question 57

Define tephra

Answer 57

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

Question 58

Outline volcanic eruptions

Answer 58

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 59

Define pyroclastic flows

Answer 59

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