Global Hazards Theory Flashcards
Define natural hazard
A natural hazard is an extreme natural event that can cause loss of life, extreme damage to property and disruption to human activities.
Define low/high air pressure
Low air pressure belts have warm, rising air.
High air pressure belts have cool, falling air.
Define winds
Winds are large scale movements of air from areas of high pressure to areas of low pressure.
Outline the global atmospheric circulation system
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.
Define trade winds
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.
Define westerlies
Westerlies are surface winds blowing towards the poles in the Ferrell cells (from NW or SW).
Define prevailing winds
Outline climate zones
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.
Define albedo effect
How does global atmospheric circulation lead to extreme weather?
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.
Define tropical storm (aka hurricane, typhoon, cyclone)
A tropical storm is an intense low pressure weather system with heavy rain and strong winds that spiral around the centre.
Describe formation of tropical storms
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.
Describe the distribution of tropical storms
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.
Describe the frequency of tropical storms
The annual number of tropical storms varies with no overall trend over the last 130 years.
Define El Niño
El Niño events occur every 3-4 years on average, lasting for 9-12 months, weakening or reversing the normal conditions in the Pacific.
Define La Niña
La Niña events occur every 2-7 years, strengthening the normal conditions over the Pacific.
Outline normal conditions in the Pacific
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.
Define drought
A drought is a long period of below average rainfall.
Define depression
A depression is a weather system that can cause rain.
Define anticyclone
An anticyclone in a high pressure weather system that can block depressions to cause drought.
Describe the distribution of drought
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.
Describe the frequency of drought
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.
Define inner/outer core
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.
Define upper/lower mantle
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.
Define crust
The crust is the outer layer of the Earth, between 10-70km thick.
Define lithosphere
Define tectonic plate
Tectonic plates are slabs into which the crust is divided that float on the mantle.
Define convection currents
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.
Define oceanic crust
Oceanic crust is thinner and more dense than continental crust.
Define continental crust
Continental crust is thicker and less dense than oceanic crust.
Define plate margin
A plate margin is a place where tectonic plates meet.
Describe destructive plate margins
Destructive plate margins are where an oceanic plate and a continental plate are moving towards each other, creating a subduction zone.
Describe subduction zones
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.
Define fold mountains
Fold mountains are formed as plates are folded and forced upwards at collision plate margins.
Describe collision plate margins
Collision plate margins are where two continental plates are moving towards each other, creating fold mountains.
Describe constructive plate margins
Constructive plate margins are where two plates are moving away from each other. Magma rises and cools to create new crust.
Describe conservative plate margins
Conservative plate margins are where two plates are moving sideways past each other at different velocities. Crust is neither created nor destroyed.
Define hot spot
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.
Define focus
The focus is the point in the Earth where tension built at a plate margin is released, from which seismic waves spread out.
Define shallow focus
A shallow focus is between 0 - 70km below the Earth’s surface, resulting from tectonic plate movement.
Define deep focus
A deep focus is between 70 - 700km below the Earth’s surface, resulting from previously subducted crust heating up or decomposing.
Define epicentre
The epicentre is the point on the Earth’s surface directly above the focus.
Define seismic waves
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.
Define Richter Scale
The Richter scale is an outdated measure of the energy released by an earthquake.
Define moment magnitude scale
The moment magnitude scale is the currently adopted measure of the energy released by an earthquake.
Define Mercalli Scale
The Mercalli scale is a measure of the effects of an earthquake.
Define seismograph
Define lava
Lava is magma above the Earth’s surface.
Define composite volcanos
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.
Define acid lava
Acid lava, erupted from composite volcanoes, is thick and sticky, so can’t flow far.
Define shield volcano
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.
Define basic lava
Basic lava, erupted from shield volcanoes, flows quickly and spreads over a wide area.
Define magma chamber
A magma chamber is a pool of magma formed at a subduction zone as the oceanic plate is melted and destroyed.
Define vents
Vents are cracks in the crust at subduction zones through which magma from the magma chamber rises to form a composite volcano.
Define tephra
Tephra is any and all fragmental material released from a volcano in an eruption.
Outline volcanic eruptions
Volcanic eruptions release lava and gases. Some also emit lots of ash, which can cover land, block out the Sun and form pyroclastic flows.
Define pyroclastic flows
Pyroclastic flows are super-heated currents of gas, ash and rock.
