2B.4a,b tides and wave processes Flashcards
Tides,
what are tides?
the alternate rise and fall of the level of the sea
what are tides caused by?
the gravitational pull of the moon and partly by the sun
when do high tides occur?
when the moon and sun are in alignment, there is the biggest gravitational pull.
when are storm surges created?
- high tides
- strong onshore winds
- high levels of wave energy
- low pressure weather systems
- low lying coastlines experience the worse
what are waves?
they are simply energy moving through water
what does the wave size depend on?
the strength of the wind, the duration the wind blows for, water depth and wave fetch.
where are the UK’s largest waves?
In Cornwall, they have travelled 4,000 km across the Atlantic Ocean from Florida, there is a long fetch.
how can wave fetch cause different rates of coastline recession?
- the longer distance waves have travelled, the more energy they have, meaning they are more powerful, increasing erosion. this increases hydraulic action and abrasion
describe how a wave breaks
-friction between the sea bed begins to distort the wave par tide orbit from circular to elliptical and slows the wave down.
-the wave depth decreases, and velocity slows
-crest begins to move forward faster than the trough
-crest outruns the trough so the wave breaks
what is a swash?
the wave breaks in nearshore zone and water flows up the beach
what is a backwash?
the wave loses energy and gravity pulls the water back down the beach
features of constructive waves
-low wave in proportion to length
-weaker backwash
-stronger swash
-the wave ‘spills’
-there is a ridge
-the wave deposits and builds up beaches
-increases the gradient of the beach in its lower section
features of destructive waves
-high wave in proportion to length
-stronger backwash
-weaker swash
-the wave ‘plunges’
-there is a steep profile
-the wave destroys the beach and erodes
-the beach profile becomes gentler in its lower section
wave length
the average distance between a successive wave crests
wave height
the vertical distance between a wave trough and wave crest
what does a beach profile show?
the gradient from the back of the beach to the sea and the characteristics in between.
describe the summer beach profile
-steeper beaches
-built up berms
-weaker backwash
-more sediment deposited
describe the winter beach profile
-higher frequency waves, more stormy waves
-berms are eroded quickly
-strong backwash
-sediment is transported offshore.
hydraulic action
water enters cracks in the rock, forcing it open, air becomes trapped ad greater force is experienced in the next cycle of compression
-dislodges blocks of rock from the cliff face
-high energy waves are more effective
-joints in igneous rocks are attacked
abrasion (corrasion)
a wave picks up sediment and throws it against rocks, hurling rocks against the cliff faces, fragments break away
-effective with high energy destructive waves
-soft sedimentary rocks are eroded most quickly by abrasion
solution (corrosion)
water in waves dissolves rock minerals, they are carried away by the wave in a solution
-most effective with constructive waves, spilling waves increases the time for the chemical reaction to occur
attrition
transported material is eroded through collision with other load items, breaking down sediment into smaller sized particles
-occurs in the foreshore and nearshore zones- swash and backwash
-soft rocks are eroded faster into silt and sand grains
