Global Hazards Flashcards
what happens in areas of high pressure
- Air cools and becomes denser and sinks to the ground = increasing air pressure
- Air warms up, and clouds evaporate
- Clear skies and dry, calm weather
what happens in areas of low pressure
- hot air rises, cools and condenses = forming clouds
- eventually this falls as precipitation
where is the Hadley cells
- largest cell extending from equator to between 30 degrees and 40 degrees north and south
what happens in the Hadley cell
- Near equator, trade winds meet and warm air rises and forms thunderstorms
- from top of storms, air flows towards higher latitudes, where it becomes cooler and sinks over tropical regions
where is the Ferrel cell
middle cell, occurs from edge of hadley cell to between 60 degrees and 70 degrees
what happens in the ferrel cell
- moves in opposite direction to Hadley and polar
- air joins the sinking air of Hadley cells and travels at low heights to mid-latitude where it rises along the border with cold air of polar cell
- air then flows back towards low latitudes in direction of equator
where is the polar cell
- smallest and weakest cell
- extends from the edge of ferrel cell to poles at 90 degrees
what happens at polar cell
- air sinks over the highest latitudes at the poles and flows out towards the lower latitudes
Where are tropical storms found and what are the conditions for a tropical storm to be formed
- between 5 degrees and 15 degrees north and south of the equator
- Temperature of ocean water around 27 degrees Celsius
- depth of ocean at least 50-60m
- 500km away from the equator
what is the coriolis effect
the effect of earth’s rotation on the direction of winds and currents
In which direction do the winds deflect in the northern and southern hemisphere
- northern hemisphere - winds deflected right
- southern hemisphere - winds defected left
what is thermocline
the point at which the temperature changes from warmer surface waters to deeper, colder water.
what is a drought
a prolonged period of time with unusually low rainfall; occur when there is not enough rainfall to support people or crops.
what causes a drought
- when regular weather have been disturbed - may be an above average presence of dry,high pressure system
- El Nino - brings descending air and high pressure over indonesia and Australia
- ITCZ - due to the shifting of the ITCZ. This area will experience high pressure, which prevents the formation of rain clouds
what is the ITCZ
- intertropical convergence zone
- low-pressure belt which encircles the globe around the equator - it is where the trade winds from NE and SE meet
what happens when two trade winds meet at the ITCZ
Heavy precipitation and thunderstorms as hot, dry air and warm, moist air combine
what are the layers in the earth
crust , mantle , outer core , inner core
describe the features of the inner core
a solid layer of iron and nickel, 6000 degrees
describe the features of the outer core
- liquid layer, ( 4030 - 5730 degrees)
describe the features of the mantle
hot, dense liquid rock (magma) that convects due to heat from core
describe the features of the crust
(lithosphere) - solid, rocky shell, fragmented into tectonic plates
describe the slab pull theory
- The newly formed oceanic crust is hot and less dense and moves outwards, forcing plates apart ( ridge push)
- older oceanic crust becomes colder and more dense = it subducts ( sinks ) into the mantle
- as dense, cold oceanic rock sinks due to gravity, it pulls plates apart by slab pull
what are the types of crust
- oceanic crust
- continental crust
describe the features of the oceanic crust
- found beneath oceans
- 5 - 10 km thick
- Example of oceanic crust : Pacific plate
Heavy and dense
describe the convection current theory
- heat is radiated from core and heat energy convects through mantle = churning motino
- hot mantle is less dense and rises up towards crust
- near the crust, the mantle cools and becomes denser and sinks again
- The tectonic plates on the mantle are pushed and pulled by friction ( they then collide or separate )
describe the features of the continental crust
- found beneath land
- 25-100km thick
- Example of continental crust : North American plate
- lighter and less dense
What happens at a destructive ( convergent ) plate boundary
two plates push together and converge
- denser oceanic crust subducts and sinks below less dense continental crust
- as it sinks into mantle, it rubs and causes friction
- this melts the plate and creates magma
- magma erupts from surface as lava, causes volcanoes
- earthquakes also felt due to stress from friction of plates
what is a plate boundary
where two ( or more ) plates meet
What happens at collision zones
two plates push together but are of the same density
- causes land to squeeze upwards, creates fold mountains
- severe earthquakes can occur as ground reshapes due to pressure
what happens at constructive ( divergent) plate boundary
plates separating by moving away from each other
- as plates move apart, magma erupts through fissures and faults
- causes volcanoes
What happens at the conservative ( transform ) plate boundary
plates slide past each other slowly
- rough edges snag and stick like velcro
- causes friction and stress to build up until one snaps and jolts forwards
- causes violent earthquakes, and releases energy through seismic waves
what is an example of a plate at a destructive boundary
oceanic plate
Eurasian
what is an example of an area at a collision zone
himalayas
what is an example of an area at a constructive boundary
Iceland
mid atlantic ridge
what is an earthquake
a violent shaking of the Earth’s crust
what is an example of a plate at a conservative boundary
Sant Andreas Fault
East Africa Rift
what is the focus
The point inside the Earth’s crust where the earthquake originates from
what is a shallow focus
- focus that is close to the Earth’s surface and therefore likely to cause more surface damage
what is a deep focus
- a focus that causes less damage as the energy has to travel further before reaching the surface
what is the epicentre
the point on the surface of the land directly above the focus ( it is also where the earthquake is felt strongest )
what are factors which control how strong the earthquake is felt at the epicentre
- how deep the focus is
- how violent the “ snap “ is at the focus
What are the effects of earthquakes
- tsunamis ( secondary effect)
- landslides /avalanches ( secondary effect )
- liquefaction ( secondary effect )
- ground shaking ( primary effect )
what are primary effects
effects which occur instantly and as a direct result of the hazard
what are secondary effects
consequences as a result of primary effects
what are the factors that depends on the damage created by an earthquake
- distance from the epicentre ( further from the epicentre , seismic waves are weaker )
- geology - softer geology will shake more easily and lose more strength than stronger geology
- Building design and infrastructure
- level of economic development of the area ( AC ‘s have a lower death toll but. larger economic loss in comparison to LIDC)
what does the richter scale measure
measures the power of the shaking based on measurements using a seisometer
what type of scale does the richter scale use
a logarithmic scale ( for every whole number of increase, the power of shaking increases by 10
what does the Mercalli scale measure
measures the intensity of the impacts of the earthquake and is based on perception of the effects on humans , buildings and environment
what is a limitation of the Mercalli scale
it can be subjective as it is based on perception and not measurable data
what is a volcano
an opening in the Earth’s crust through which lava, ash , steam , rock particles and gas are erupted from the mantle
where do volcanoes occur
along plate boundaries or on hotspots
what are the types of volcanoes
- composite
- Shield
- Fissure volcanoes
- caldera volcanoes
-hotspot volcanoes
how do caldera volcanoes occur
when a volcano erupts so explosively that the magma chamber empties and the crater collapses into itself
where are composite volcanoes found
at destructive plate boundaries or along the ring of fire around the Pacific Ocean, where plates move towards each other
what is the magma like of composite volcanoes
more viscous and sticky, unlike those found at constructive plate boundaries and it moves much more slowly and can lead to more explosive eruptions
where are shield volcanoes found
- found at constructive plate boundaries where plates move away from each other allowing hot liquid magma from mantle to flow up by convection and be erupted to the surface
where do fissure volcanoes occur
at constructive plate boundaries when the plates separate to leave a rift or fissure
when do hotspot volcanoes occur
occur when an oceanic plate moves over hot area of mantle
causing magma to rise upwards towards crust
- the magma can punch through and create volcanic islands
- volcano becomes extinct when oceanic plate move away from hotspot
What are the effects of volcanic activity
- lava flows
- pyroclastic flows
- lahars
- release of toxic gas emission
-tephra
how are volcanoes measured
Using the volcanic explosivity index, it looks at how far the ash plume has travelled, the volume of material ejected, and how often the type of eruption occurs
what is tephra
Fine, volcanic dust which tends to deposit near the volcano but can blow in the wind across nations and can interact with the atmosphere , leading to climate change
what are lava bombs
’ bombs’ of ejected lava that cool on the outside to form a crust and explode as liquid rock
what are volcanic gases
mixture of sulphur dioxide , carbon dioxide, water vapour , nitrogen which can poison soil and water and cause respiratory problems in humans and even interact with the weather
what are lahars
mudflows created when water and volcanic ash mix - can be very fast and bury areas beneath mud
what are ash clouds
combination of volcanic glass and debris which can travel miles high in atmosphere and interfere/ reduce sunlight
what is pyroclastic flows
hot , rocky gas and ash cloud from explosive eruptions which can travel over 300 km/h and reach 800 degrees
what are sulphur deposits
solid sulphur rock which are ejected/deposited from fumaroles which can be used in industry - Sulphur mining can create jobs
how can a volcano be useful
- can increase in tourism
- can create geothermal power
- volcanic ash will erode to form fertile soil for agriculture
how can an earthquake be predicted
- installing sensitive seismometers
- observing unusual animal behaviour
- radon gas emission
- map epicentres and frequencies and look for patterns
what are some ways a building can resist the earthquake effects
- counter weight on roof to balance out swaying
- automatic window shutters to prevent falling glass
- hollow concrete bricks to minimise damage if they fall
- foundation made of steel pillars, ball bearings, rubber
- automatic sprinkler system and gas shut off to prevent fires
- roof made of reinforced cement concrete
how can volcanic eruptions be predicted
- seismometers - measuring the pattern of earthquakes near the magma chamber
- gas emission - particularly sulfur and carbon dioxide; these increase as magma increases
- soil or water pH - soils and water sources may become more acidic as the sulphur content increases
- tiltmeters - measure the shape of volcanoes to detect bulges
Historic methods are used to identify any patterns
What can be done to buildings to reduce volcanic damage
- Buildings can be insulated, barriers can be put in place to reduce ash entry, and gas masks can be made available
- Roofs can be reinforced to cope with the weight of ash without collapsing
what is continental drift
the process of plates moving over time , causing the changing relative positions of the continents
How can human activities make droughts worse
- excessive irrigation
- dam building
- over -grazing exposes soil to wind erosion
- deforestation - reduced transpiration = reduces the soil’s ability to hold water so it dries out
-Soil erosion impacts the ability of the soil to capture and store water - Overfarming and intensive farming
what happens during an el nino season
- Trade winds weaken, stop or even reverse in the western Pacific
- The piled-up warmer water around Australasia makes its way back eastwards across the Pacific
- rising warm,moist air brings rainfall and possibility of floods to south America
- descending air brings warm , dry weather and droughts to Australia
What happens during a La Nina season
extreme versions of normal conditions in the pacific ocean
- trade winds strengthen
- extreme weather conditions mean results of droughts in south America, and floods in Australia
what are the normal conditions in the pacific ocean
- trade winds blow. towards warm water of western pacific
- rising air occurs at this locatino as a result of water heating up atmosphere
- trade winds across surface of pacific push warm water westwards from peru to australia
- in eastern pacific the shallow position of thermocline allows winds to pull water up from below
- because of the pressure of the trade winds pushing water westwards the sea temperature in Australasia becomes warmer
how do we know if it is an el nino year
- better satellite coverage is used to look for oceanic patterns
- design of buoys has improved and they can now measure sea surface temperatures, surface winds, air temperature and humidity
- biological records use - during el nino phytoplankton dont grow as there is no upwelling of cold water in eastern pacific
