Global Hazards

hemisphere -

a half of the earth, usually as divided into northern and southern halves by the equator

weather -

The condition of Earth's atmosphere at a particular time and place. (eg, temperature, precipitation, cloud cover)

climate -

The average (expected) weather conditions in an area based on data collected over 30 years or more.

troposphere -

an area of the atmosphere from the Earth's surface to a height of 10-15km in which the weather takes place

climate zone -

divisions of the Earth's climates into belts or zones, according to average temperature and average rainfall. The three major zones are polar, temperate and tropical.

latitude -

the imaginary lines that surround the earth ranging from 0° at the equator to 90° at the poles

low pressure -

caused when air is rising, so less air is pressing down on the ground; air rises as it warms, leading to low pressure at the surface.

high pressure -

when there is more air pressing down on the ground, caused by air sinking; air descends as it cools, leading to high pressure at the surface.

condensation -

the process by which rising water vapour becomes a liquid.

precipitation -

the collective term for moisture that falls from the atmosphere; this could be in the form of rain, snow, sleet or hail

Hadley cell -

a system of vertical and horizontal air circulation that creates major weather patterns, predominantly in tropical and subtropical regions

Ferrel cell -

air circulation cell found at midlatitudes (between 30° and 60°) between Hadley and Polar cells.

Polar cell -

air circulation cell found between 60° and 90°, air rises at lower latitude and sinks at poles.

front -

a boundary separating two masses of air with different densities, usually heavier cold air and lighter warm air.

trade winds -

the prevailing pattern of easterly surface winds found in the tropics within the lower section of the Earth's atmosphere.

prevailing wind -

the most frequent, or common, wind direction

rain shadow -

an area or region behind a hill that has little rainfall because it is sheltered from rain bearing winds.

monsoon -

heavy rainfall that arrives as a result of seasonal wind, notably in southern Asia and India between May and September.

Katabatic winds -

movements of cold dense air that flow downhill and along valley floors; in Antarctica, most winds blow towards the coast from the centre.

El nino -

climatic changes affecting the Pacific region and beyond every few years, characterised by the appearance of unusually warm water around northern Peru and Ecuador, typically in late December; the effects include the reversal of wind patterns across the Pacific, causing drought in Australasia and unseasonal heavy rain in South America.

thermocline -

the point at which the temperature changes from warmer surface waters to deeper, colder water.

droughts -

a prolonged period of time with unusually low rainfall; occur when there is not enough rainfall to support people or crops.

La nina -

A climate event in the eastern Pacific Ocean in which surface waters are colder than normal.

tropical storm -

a strong depression (low pressure system) with wind speeds of between 39-74 mph, usually form over tropics where water is warm.

Coriolis effect -

the result of Earth's rotation on weather patterns and ocean currents, making storms swirl clockwise in the southern hemisphere and anticlockwise in the northern hemisphere

intertropical convergence zone -

a low-pressure belt that encircles the globe around the Equator; its is where the trade winds from the northeast and southeast meet; the Earth is tilted on its orbit around the Sun, causing the ITCZ to migrate between the Tropics of Cancer and Capricorn with the seasons.

heatwave -

a prolonged period of abnormally hot weather

super typhoon -

a storm that reaches sustained wind speeds of at least 150 mph.

Emerging and developing country -

countries which neither share all the economic development characteristics required to be advanced or are eligable for the Poverty Reduction and Growth Trust; EDCs are classified by the IMF

primary industries -

an economic activity that involves collecting raw materials, such as fishing, farming and mining

inner core -

the centre of the earth with a solid metal inner core (at 6000°C temperature) composed primarily of iron and nickel

outer core -

semi-solid outer core (4030° - 5730°C) from which heat is radiated outwards from the core to the mantle

mantle -

hot, dense liquid rock (magma); it is continuously moving due to heat from the core (convection), which drives plate movement.

crust -

the solid, rocky shell layer (lithosphere) over the mantle around the Earth, upon which sit our continents and oceans; it is fragmented into tectonic plates that float on the mantle.

radiated -

energy emitted outwards from a central point in waves or rays.

convection -

the constant churning of the mantle through heat energy (radiation) passing out from the core

tectonic plates -

Sections of the Earth's crust that move due to convection currents. (7 major and many small or micro)

oceanic plate -

the lithosphere (crust) which is underneath oceans. Thinner, denser, newer, able to be subducted, destroyed and created

continental plate -

the lithosphere (crust) upon which sits our continents and land. Thicker, less dense, older, unable to be subducted, or renewed.

continental drift -

the movement of continents and tectonic plates, which is driven by convection in the mantle.

plate boundary -

the area where two or more tectonic plates meet, and where hazards such as earthquakes and volcanoes, and mountain building, can be found

landform -

a natural, recognisable feature of the Earth's surface

hazard -

something posing a danger or risk to human life or property

tectonic hazard -

includes volcanic eruptions, earthquakes and landslides

subduction -

the sinking of a dense plate (oceanic) into the mantle

destructive boundary -

Where an oceanic plate subducts underneath a continental plate or another oceanic plate as they move towards each other. Friction in the Benioff zone causes the plate to melt as it is subducted into the mantle.

collision zone -

when two continental plates move towards each other, neither can be subducted, leading to collision, fold mountains and earthquakes.

constructive boundary -

when plates move apart allowing magma to rise in the gap and solidify creating new crust as it cools.

conservative boundary -

also called a transform boundary where two plates move in opposite directions or in the same direction at different speeds. Move in a lock and slip motion causing periodic earthquakes.

fissure -

a narrow opening in the Earth's crust caused by splitting (e.g. because of tectonic movement)

fault -

like a fissure, this is a split in the rock; in plate tectonics this is where the plates are moving, e.g. San Andreas

friction -

when plates slide past one another, they create heat and stress, which will lead to rock melting and fracturing.

seismic waves -

a wave of energy passes through the earth or along its surface due to plate movement.

focus -

the location in the earth where earthquakes start

epicentre -

the point on the Earth's surface directly above the focus

primary effects -

the immediate consequences of a hazard, e.g. a earthquake causing a house collapse

secondary effects -

follow-on consequences of hazards, for example a fire from a gas pipe broken during a house collapse.

impacts -

the effects of an event, usually classified as Social, Economic or Environmental

short-term impacts -

the effects immediately after an event, usually within one week

long-term impacts -

the effects over a longer time scale, usually months or years later

Richter scale -

a logarithmic scale with no upper limit that rates an earthquake's magnitude based on the size of its seismic waves

Mercalli scale -

A subjective scale that rates earthquakes according to how much damage they cause at a particular place

seismometer -

an instrument that measures and records ground motion; used to determine the magnitude and location of an earthquake

hotspots -

weaknesses in the Earth's crust where rock is thinner, which allows magma to surface even though it is not at a plate boundary

composite volcanoes -

a narrow based, steep sided volcano with a structure consisting of alternating layers of ash (tephra) and lava. Formed by explosive eruptions

shield volcanoes -

a wide based volcano with long, gently sloping sides formed by effusive eruptions of hot lava (1,200°C) with low viscosity

viscosity -

a measure of a liquids resistance to flow. Low = runny, High = gloopy

fissure volcanoes -

a volcano which occurs at constructive plate margins, does not form a cone, instead, lava flows out along a fault line.

Volcano Explosivity Index -

a measure of the explosivity of volcanic eruptions.

Tephra -

fragments of rock, ash, lava created by volcanic eruptions

Lava bombs -

Large fragments of molten lava thrown into the air by explosive eruptions which can land several miles away from the volcano

Volcanic gasses -

gasses emitted by volcanoes including: H₂O, CO₂ and SO₂

Lahars -

volcanic mudflow of debris mixed with water, covering the land in thick, dark volcanic material.

Jokulhlaups -

glacial outburst flood triggered by volcanic activity melting a glacier or ice cap.

ash clouds -

small particles of fractured rock injected into the atmosphere which eventually settle. Can travel long distances depending on the size of the eruption.

sulphur deposits -

often found near fumeroles which can be used in industry and provides jobs in some parts of the world.

geothermal power -

power generated by capturing the heat of the earth, usually by harnessing steam and using it to drive turbines.

Pyroclastic flow -

an avalanche of ash and hot, toxic expanding gas, traveling very fast down the flank of a volcano

Lava flows -

sheets of molten rock that flow over the ground surface and then solidify.

glacier -

a frozen river of ice formed by snow and ice accumulating in mountains or polar areas, which can even form on top of volcanoes (e.g. in Iceland)

sub-glacial -

refers to processes or landforms underneath a glacier.

mitigation -

the action of trying to reduce the impact of a hazard, by planning, predicting and preparation (e.g. building earthquake-resistant buildings)