geog coasts Flashcards
whats wave frequency
number of wave crests passing a certain point in a minute.
whats wave period
amount of time taken for the wave crest at point A to reach point B
whats a sediment cell
a self-contained strech of coast. sediment moves around a cell but not usually from one cell to another. A new sediment cell is usually marked by a barrier such as a change in wind direction or a landform e.g. a headland
what do sediment cells help
us to manage coastal defences
whats carbonisation
when CO2 in this atmosphere dissolves in rainwater and created carbonic acid that can dissolve rocks e.g. limestone.
where is carbonisation increased
in vegetated areas as the porous soils hold high amounts of CO2 due to the decomposing plant debris
what is root action
the roots of plants growing into cracks and joints in rocks and exerting pressure that eventually breaks the rocks apart
what is burrowing
worms and other vertibrate bringing soil and rock particles to the surface which facilitates for chemical weathering at greater depths
what is salt crystalisation
salt-water getting forced into the cracks of rocks, the water being evaporated and leaving the salt behind which applies pressure and eventually breaks the rock
what’s freeze thaw
water forced into the cracks of rocks. when it freezes, it expands by 9% which applies pressure to and eventually breaks the rocks.
what’s a eustatic change
a global change is sea level due to the exchange of water between the worlds oceans, ice caps and glaciers.
what’s a isostatic change
a local change in the level of land due to the earths crust attempting to reach dynamic equilibrium. this usually occurs due to the loading/unloading of ice and changes sea levels
what’s thermal expansion and how does it increase sea levels
oceans absorbing heat from the atmosphere which causes the water molecules at the surface to expand. the oceans absorb 90% of heat which causes water to expand.
how does sea-floor spreading increase sea levels
when magma rises and creates a new ocean floor this pushes water upwards
how do earthquakes increase sea levels
can lead to the sudden displacement of the earths crust vertically
what is accretion and how does accretion increase sea levels
the creation of new landmasses due to the deposition of sediment. this keeps areas at pace with rising sea levels
how does subsidence of ground increase sea levels
soils and land sinking downwards means that sea levels will increase more.
how much are sea levels rising in the kiribati and how far is the island away from sea level
1.2cm a year
the island is only 2m above sea level
people are displaces and climate refugees are created
what’s happening in jakarta
the capital of indonesia is a megacity with 32mill inhabitiants and people are illegally draining underground aquifers because they don’t have access to public water. this is leading to the ground sinking 25cm a year and is expected to have most of the city underwater by 2050
average sea level rise
3-4mm annually
what have rates of erosion on the river nile delta increased from and to
25m to over 200m
what is a wind wave
a wave generated by immediate local winds that’re not sustaining and will stop when the wind stops
what is a swell wave
a self-sustaining wave thats generated by energy below the oceans surface and do not need local winds to be created.
why do waves break
they break in shallow water because the crest of the wave begins to move faster than the trough, which experiences friction from sediment and eventually the wave topples forwards
what is flocculation
small, fine particles (like clay) are suspended in the water but clump together due to the electrostatic attraction. these form larger particles that sink.
what is gravity settling
energy of waves is weaker than the force of gravity, so the waves are forced to drop the sediment they’re holding. the larger particles are dropped first, then the smaller ones
what is wave refraction
when waves approach shallow water they slow down due to friction. waves approach the coastline and bend which causes them too loose energy. e.g. waves energy is concentrated on a headland and disperces wave energy into bays.
human causes of flooding
- removal of vegetation e.g. mangroves
- over-abstraction of underground aquifers that leads to subsidence of ground
- lack of defences
- climate change
- over-population
- subsidence and the clearing of land
- industrialisation
engineering projects
physical causes of flooding
- topography
- height of land
- storm events and tsunamis
