geography tectonics

keywords 4 tectonics

areal extent

the area over which damange occurs or a hazard is felt

andesite

typically found in lava flows produced by stratovolcanoes. generally formed after an oceanic plate melts during its descent into the subduction zone

ash

the very fine particles of rock ejected during a volcanic eruption. these particles form part of the tephra, which is a term for all sizes of ejected volcanic material

asthenosphere

the part of the mantle, below the lithosphere, where the rock is semi-molten

basalt

fine-grained, igneous rock, underlying more of the earth’s surface than any other rock type, especially ocean basins. associated mainly with constructive plate boundaries.

Benioff zone

the area where friction is created between colliding tectonic plates, resulting in intermediate and desp earthquakes.

collision plate boundary

where two plates move towards each other causing a very slow collision which is likely to cause folding and faulting of crustal rocks and the uplift of continental crust to form fold mountains.

community preparedness/adaptation

people within communities, either whole or parts of settlements, work together to change their way of life so that the impact of a tectonic hazard event is not as hazardous

conservative plate movement

where two plates meet and move alongside each other in a similar direction or opposite direction, usually at different speeds. friction between the two plates is great and stresses and strains build up to create shallow earthquake foci. also transform plate boundary.

constructive plate boundary

where two plates move in opposite directions, leaving a zone of faulting and a gap into which magma from the asthenosphere rises. also divergent plate boundary.

convection currents

hot, liquid magma currents moving in the asthenosphere

convergent plate boundary

where two plates move towards each other and at the boundary the denser oceanic plate (basaltic) is subducted beneath the less dense continental plate (granitic), creating surface features such as a trench, and deep features such as the benioff zone. also destructive plate boundary.

crustal fracturing

when energy released during an earthquake causes the earth’s crust to crack

epicentre

the point on the earth’s surface directly above the focus of an earthquake

focal depth

the depth at which an earthquake starts (focus). it is divided into shallow. intermediate and deep. shallow earthquakes have the greatest impacts, as the seismic waves have not lost as much of their energy by the time they reach the surface.

focus

the point inside the earth’s crust from which the pressure is relased when an earthquake occurs

geological structure

the arragenemnt of rock in layers, or folds and the joints and bedding planes within them

hazard-management cycle

a theoretical model of hazard management as a continuous four stage cycle involving mitigation, preparataion, response and recovery

hazard profile

an analysis of different types of hazard, or actual events, based on a range of criteria. this allows a useful comparison to be made.

hazard-response curve

*see park model (wtf this is so stupid)

hotspot

points within the middle of a tectonic plate where plumes of hot magma rise and erupt.

hydrometeorological hazards

natural hazards caused by climate processes (including droughts, floods, hurricanes and storms)

intra-plate earthquakes

earthquakes which occur far from plate margins

l waves

the slowest seismic waves which focus all their energy on earth’s surface

lahar

a mixture of meltwater from snow and ice on top of an active volcano and tephra (volcanic material such as ash) from eruptions that travels very quickly down existing river valleys, reaching some distance away from the volcano

land use zoning

a process by which local government regulates how land in a community may be used

landslide

a mass movement fo rock and soil down a steep slope under the influence of gravity, perhaps triggered by an earthquake loosening material

lava flow

molten magma that reaches the earth’s surface is known as lava. it will flow down the sides of a volcano until it cools and solidifies. basaltic lavas flow faster than adesitiv lavas, for example, because of the different velocities.

liquefaction

when the violent shaking during an earthquake causes surface rocks to lose strength and become more liquid than solid

lithosphere

the solid layer, amde from the crust and upper mantle, from which tectonic plates are formed

magnitude

the amount of energy released by a tectonic event. for earthquakes this is best measured on the moment magnitude scale and for volcanoes the volcanic explosivity index

mass movement

the downward movement of material under the influence of gravity. it includes a wide range of processes such as rockfalls, landslides and solifluction.

mega-disaster

an extreme disaster which can impact globally. for example, the scale of the impacts is unusually great or very severe with huge numbers of deaths, loss of buildings and infrastructure, or long-lasting impacts on normal social and economic systems

mercalli scale

an earthquake intensity scale based on 12 levels of damage to areas

mitigation

action to reduce the impacts of an event

modify loss

reduce the impacts of losses experienced from a tectonic hazard, for example by insuring belongings and property

modify the event

alter the natural hazard itself in order to change its likely impacts. earthquakes cannot be changed, but some volcanic activity can be modified, such as by diverting lava flows.

modify vulnerability

vulnerability is a key factor in determining the impact of a hazard, so making people less vulnerable will reduce the scale of a disaster

moment magnitude scale

the most accurate earthquake magnitude scale, it measures the total energy released by an earthquake

multiple-hazard zone

an area that is at risk from multiple natural hazards such as hurricanes and earthquakes

natural hazard

a physical geographical event, tectonic, hydrological, or meteorological, which has a negative impact on people through causing injury or deaths, loss of property, or disruption to the normal way of life.

p waves

the fastest seismic waves which travel through both solids and liquids

paleomagnetism

the study of past changes in the earth’s magnetic field

park model

shows how a country or region might respond after a hazard event

pressure and release model

a tool used to work out how vulnerable a country is to hazards. a model developed by blaikie et al (1994). it depicts a disaster as a produce of physical exposure and socio-economic pressure

rapid onset

a hazard that happens very quickly with no or little warning eg an earthquake

resilience

the ability of a community to resist the impacts of a hazard and overcome or recover from a setback or hazard, by adapting and recovering

retrofitting

adding something to a building after it was built to help it withstand tectonic events

S waves

seismic waves which only trravel through solids and move with a sideways motion

sea floor spreading

the movement of the oceanic crust away from a constructive plate boundary, as recorded by the magnetic stripes in the basaltic rock (paleomagnetism)

slab pull

when newly formed oceanic crust sinks into the mantle, pulling the rest of the plate further down with it.

slow onset

a hazard that happens very slowly with plenty of evidence and warning, such as drought

spatial predictability

the extent to which the location of a hazard can be known in advance; this is generally easy for a volcano but less so along fault lines

speed of onset

the time between an event occurring and it being felt, eg an earthquake can be instantaneous, whilst a tsunami wave may take some time to arrive

sub-aerial processes

the processes of weathering and mass movement

subduction zone

the area in the mantle where a tectonic plate melts

threshold

in this context, the level of resilience a community has before it is overwhelmed by a disaster

transform fault

a fault created on a large scale when two plates slide past eachother

volcanic explosivity index

the scale used to measure the magnitude of a volcanic eruption

water column displacement

the movement of a volume of seawater above the point at which the seabed was moved up or down by an earthquake, such as a thrust