Geography Edexcel IAL - World at risk

Accretion Wedge

The accumulation of material at the point of subduction

Anticyclone

A system of high pressure, causing high temperatures and unseasonably high

evaporation rates

Aseismic Buildings

Buildings designed to withstand or minimise destruction during an

earthquake

Asthenosphere

The upper mantle layer of the Earth. It is semi-molten and approximately 2000km

wide

Ash

Fine particles and dust ejected during an eruption, which can remain airborne as clouds or

accumulate on the ground

Channel Flow

Water flowing in a rivulet, stream or river

Continental Crust

Crust that forms the continents of the lithosphere, on average 35km thick

Continental Drift

The movement of tectonic plates, due to varying weights of crust. It was

originally thought that convection currents caused the movement of the plates, but now Slab Pull is

thought of as the primary driving force

Convection Currents

The circulation of magma within the mantle (asthenosphere). Magma is

heated by radioactive processes in the core and cools at the surface, and so circulates between the

two places

Convectional Precipitation

Solar radiation heats the air above the ground, causing it to rise, cool

& condense forming precipitation (often as thunderstorms)

Degg's Model

This model shows that a hazard becomes a disaster if it affects a vulnerable

population

Depression

A system of low pressure, with fronts of precipitation where low and high pressure air

masses meet

Drainage Basin

The area of land drained by a river and its tributaries

Drainage Density

The total length of all rivers & streams divided by the area of the drainage basin

Drought

An extended period of deficient rainfall relative to the statistical average for the region

(UN)

Economic Water Scarcity

When water resources are available but insufficient economic wealth

limits access to it

Enhanced Greenhouse Effect

The build-up of greenhouse gases in the atmosphere, reducing the

amount of solar radiation reflected into space

ENSO Cycles

El Nino Southern Oscillations, naturally occurring phenomena that involves the

movement of warm water in the Equatorial Pacific

Epicentre

The point on the surface, directly above the earthquake's origin

Focus

The place in the crust where the pressure/seismic energy is released

Glacial Period

A period of time of colder average global temperatures causing the growth of ice

cover, glacial advances and sea levels to fall

Hazard Mitigation Cycle

The sequence of governance of a natural hazard: monitoring &

prediction, mitigation, preparedness

Holocene Epoch

Our current glacial period of limited ice cover, lasting over 10,000 years

Hot Spot

strong and rising currents of magma that can create volcanic activity and break through the earths crust

Hydrological Drought

Insufficient soil moisture to meet the needs of vegetation at a particular

time

Interglacial Period

A period of time of warmer average global temperatures, resulting in reduced

ice cover, glacial retreat and sea levels to rise

Jokulhaup

A sudden glacial flood caused by a glacier on top of or near a volcano melting due to

the heat from the eruption

Lahar

A flow of mud and debris

Lithosphere

The upper crust of the Earth (average thickness = 100km)

Love Waves

A surface earthquake wave with horizontal displacement

Meteorological Drought

When long-term precipitation trends are below average

Mid

Ocean Ridge - Parting oceanic plates at a constructive plate boundary creates a ridge, with

new land at the base of the oceanic valley

Milankovitch Cycles

Changes to the tilt and shape of the orbit will affect the average temperature

of the Earth

Moment Magnitude Scale

A measure of an earthquake's energy released, considered the most

accurate measure

Oceanic Crust

Crust, usually thinner than continental crust, that forms the sea floor. It is on

average 7km thick

Orbital Eccentricity

How far a planet's orbit is from being a perfect circle

Paleomagnetism

The alternating polarisation of new land created. As magma cools, the magnetic

elements within will align with the Earth's magnetic field, which can alternate over thousands of

years

Park's Model

A model describing the decline and recovery of a country over time, following a

natural disaster

Partial Melting

Elements within the lithosphere have different melting points, and so rock is

partially melted, partially solid

Permafrost

Permanently frozen soils throughout the year

Physical Water Scarcity

A physical lack of available freshwater which cannot meet demand

Primary Waves

An earthquake wave causing compressions within the body of rock

Pyroclastic Flow

A mixture of gases and rock fragments, at high temperatures travelling at rapid

speeds

Rayleigh Waves

A surface earthquake wave causing both horizontal and vertical displacement

Richter Scale

A logarithmic measure of earthquake's intensity

Runoff

Water flowing over the surface of the ground eg. after precipitation or snowmelt

Secondary Waves

An earthquake wave causing vertical displacement within the body of rock

Seismic Waves

The energy released during an earthquake, in the form of Primary, Secondary,

Love and Rayleigh Waves

Slab Pull

The force contributing to the movement of tectonic plates. Slab Pull is due to the weight

of the plate

Subduction

Oceanic plate is forced below continental plate, due to the oceanic plate being more

dense than the continental plate

Thermohaline Circulation

The movement of volumes of seawater from cold deep water to warm

water surface water

Tipping Point

A critical threshold where any changes to a system after the tipping point are

irreversible

Tsunami

Initial vertical water displacement (often from a submarine earthquake) creates waves,

with large destructive power

Volcanic Explosivity Index (VEI)

A measure of the magnitude of a volcano's eruptions

Volcanic Island Arc

A series of volcanoes (often in the shape of an arc) that are formed

consecutively, as a tectonic plate moves across a magma plume

Wadati Benioff Zone

A region of the subducting plate, most affected by pressure and friction,

where most destructive margin earthquakes originate