Aeolian Processes

Front 1

what are aeolian processes ?

Back 1

transportation, erosion and deposition of sediments by wind.

Front 2

where do aeolian processes take place?

Back 2

coastal zones

cold and try deserts

hot and dry deserts

where there is availability of fine sediments strong winds and sparse so not much vegetation

Front 3

where else are these processes important in ?

Back 3

other planets like mart and tital

Front 4

what is wind?

Back 4

the movement of air from high to low pressures and occurs to equalise the difference in pressure

Front 5

describe the atmospheric pressure at the earths surface:

Back 5

its the measure of the weight of the air passing down on the surface.

the greater the mass of air above us the greater the pressure

Front 6

give an example:

Back 6

the equator is very warm so air has a low density which means little pressure.

Front 7

what happens at high pressures?

Back 7

wind movement is high, and air particles sink and then move towards the low pressure environment.

Front 8

what is the principle of the rise and falling of the air?

Back 8

rising air at the equator becomes coolers before arriving at the poles and then sinks before it reaches the hadley cell

Front 9

what happens to sinking air at the poles?

Back 9

air moves to low pressure areas of the equator and becomes to warm to start rising before reaching the equator so goes to the polar cells.

Front 10

what new cell is formed from the rising air at the polar cell and the sinking air at the hadley cell?

Back 10

new cell known as the farrel cell.

Front 11

what shifts the direction of the winds?

Back 11

the Coriollis effect

this causes trade winds westerly and easterly

Front 12

how does wind transport sediment?

Back 12

wind lowers the density and viscosity than water. and causes turbulance.

Front 13

describe the characteristics of turbulent flow:

Back 13

very disordered, lots of eddies, complex swirling patterns.

Front 14

what is the logarithmic velocity profile?

Back 14

the average velocity proportional to logarithmic distance from the surface

Front 15

why is there a gradual increase in velocity?

Back 15

the fluid (air particles) in contact with the surface adheres to the surface due to friction this causes zero velocity at the contact of the surface. this causes the paarticles above to slow down

Front 16

what are the three mechanisms to move particles

Back 16

lift

drag

Bombardment

Front 17

how does lift move particles?

Back 17

its a vertical force due to the pressure difference

Front 18

what is drag?

Back 18

a horizontal force due to pressure difference and friction

wind flow from left to right have a lot of air heating up the sediment closer to the wind which causes high pressure on the windward side and low pressure on the leaward side which creates a volumeso the high pressure pushes sediment in the same direction as the wind.

Front 19

how does bombardment move particles?

Back 19

once motion has started falling particles bombard and move the others but no bonbarding before motion

Front 20

what is the friction that occurs?

Back 20

the skin friction between particles and air at microscopic levels air and soil stick together

Front 21

what happens when there is a high velocity?

Back 21

velocity has little change were as in low velocity there is lots of change.

Front 22

what happens where there is little velocity difference?

Back 22

away from the bottom there is less friction

Front 23

what is Bernullis equation ?

Back 23

potential energy (pressure) +kinetic energy (velocity ) = constant

Front 24

what happens to the pressure when there is low and high velocity

Back 24

low velocity at the bottom of sediment grain- high pressure

high velocity at the top there is low pressure so the sediment gets lifted

Front 25

when does movement start?

Back 25

when the generated force is strong enough.

Front 26

when is the generated force strong enough

Back 26

when the CRITICAL SHEAR FORCE is reached

when measuring the wind force call it CRTICAL WIND VELOCITY

Front 27

what happens when diameter increases?

Back 27

bigger the diameter the heavier the grain and so needs more energy to move it

Front 28

why would you need a high velocity at a small grain level?

Back 28

because there is cohesion and very small grains can be closer to the bottom where velocity is zero.

Front 29

what is saltation

Back 29

leaping a jumping particles

Front 30

what is creep?

Back 30

coarser particles that move near the suface roling and can be promoted by the impact of fine grains

Front 31

what is reptation

Back 31

low hopping of grains

Front 32

what is suspension ?

Back 32

very small grains thats follow turbulent motion

Front 33

what is rotation ?

Back 33

low jumping particles

Front 34

what do Aeolian bed forms depend on?

Back 34

windspeed and wind elevation

Front 35

what are Aeolian bed forms?

Back 35

factors influecning morphology

Front 36

how are ripples formed in the sand?

Back 36

controlled by grain size and wind speed.

always present unless course sediment and very high velocity on dunes.

Front 37

what causes adhesion repples?

Back 37

grains get transported over a wet or damp/ salty durface and become trapped by surface tension

small sub parallel ridges perpendicular to windflow form

Front 38

describe the characteristics of dunes:

Back 38

have a big wavelength a big wave hight and are different shapes and orientations. max height is 30 degreese

Front 39

how are they formed?

Back 39

sand movement until it finds and obstacle heaviest grain settles against it

Front 40

how can dunes migrate?

Back 40

on the windward side by erosion.

Front 41

describe transverse dunes

Back 41

dunes where lots of sand is available

Front 42

describe linear dunes

Back 42

wind comes from conversion direction

Front 43

how do parabolic dunes form?

Back 43

when there is an obstacle

Front 44

and stardunes?

Back 44

winds come in different directions