challenge of natural hazards Flashcards
structure of the earth
-crust - varies in thickness, made of several plates
-the mantle - widest layer, heat and pressure means the rock is in a liquid state that is in a state of convection
-inner and outer core - hottest section, mostly made of iron and nickel and is 4x denser than the crust
convection currents
1 radioactive decay of some of the elements in the core and mantle generate a lot of heat
2 when lower parts of the mantle molten rock heat up they become less dense and slowly rise
3 as they move towards the top they cool down, become more dense and slowly sink
4 these circular movements of semi-molten rock are convection currents
5 Convection currents create drag on the base of the tectonic plates and this causes them to move
destructive/convergent plate margin
Plates move together, When the denser plate (oceanic) subducts beneath the other, friction causes it to melt and become molten magma. Oceanic plates get stuck, causes earthquakes. The magma forces its way up to the surface to form a volcano. Creates fold mountains and ocean trenches.
Constructive/divergent plate margin
Plates move apart due to convection currents causing new magma to reach the surface through the gap. Volcanoes formed along this crack cause mountain ranges. Lava cools, new crust formed
Conservative/transform plate margin
plates slide past each other in opposite directions or the same direction at different speeds. Plates can get stuck and pressure builds, when the crust moves energy is released and causes earthquakes.
Collision plate margin (2 continental crusts)
Both plates are continental so get pushed upwards, no volcanoes as the crust is too thick but causes very powerful earthquakes.
natural hazard definition
a natural process which could cause death injury or disruption to humans property and possesions
geological hazard definition
hazards caused by land and tectonic processes
meteorological hazard
hazards caused by weather and climate
cause of earthquakes
Earthquakes are caused when two plates become locked causing friction to build up. From this stress, the pressure will eventually be released, triggering the plates to move into a new position. This movement causes energy in the form of siesmic waves, to travel from the focus towards the epicentre. As a result the crust vibrates triggering an earthquake
Epicentre definition
the point directly above the focus, where the seismic waves reach first
focus definition
the point at which pressure is released is called the focus
volcanic hazards
-ash cloud
-gas (sulphur dioxide, water -vapour and carbon dioxide)
-lahar (a volcanic mudflow which usually runs down a valley side on the volcano)
-pyroclastic flow (fast moving current of super heated gas and ash travelling at 450mph)
-volcanic bomb (a thick lava fragment that Is ejected from the volcano
managing volcanic eruptions - warning signs
small earthquakes are caused as magma rises up
temperatures around the volcano rise as activity increases
when a volcano is close to erupting it starts to release gas
managing volcanic eruptions - monitoring techniques
-seismometers are used to detect earthquakes
-thermal imaging and satellite cameras can be used to detect heat around a volcano
-gas samples may be taken and chemical sensors used to measure sulphur levels
managing volcanic eruptions - preparation
-create an exclusion zone around the volcano
-having an emergency supply of basic provisions such as food
-being ready and able to evacuate residents
-trained emergency services and a good communication system
earthquake management - prediction methods
-satellite surveying, tracks changes in the earths surface
-laser reflector, surveys movement across fault lines
-radon gas sensor, radon gas is released when plates move
-seismometer
-water table level, water levels fluctuate before an earthquake
earthquake management - protection
-earthquake resistant buildings
-raising public awareness
-improving earthquake prediction
atmospheric circulation definition
large scale movement of air by which heat is distributed on the surface of the earth
Hadley cell
largest cell which extends from the equator to between 30 to 40 degrees north and south
ferrel cell
middle cell where air flows poleward between 60 and 70 latitude
polar cell
smallest and weakest cell that occurs from the poles to the ferrel cell
low pressure
caused by hot air rising. causes stormy cloudy weather
high pressure
caused by cold air sinking. causes clear and calm weather
