Aeolian processes: incl. erosion, deposition, transportation

Question 1

what planets could have aeolian activity

Answer 1

all terrestrial planets with dynamic atmospheres- mars, venus, earth

Question 2

why is aeolian erosion and transport especially effective in deserts

Answer 2

sediment largely loose in sandy deserts and not held by vegetation due to moisture deficit, the carried sand makes the wind more erosive

Question 3

what is the kármán line

Answer 3

the line approx 100km above the earths surface that delineates the boundary of atmosphere and space

Question 4

what does it mean to say the atmosphere is in hydrostatic equilibrium

Answer 4

pressure is exerted in all directions, making it relatively stable

Question 5

layers of the atmosphere

Answer 5

thermosphere, mesosphere, stratosphere, troposphere

Question 6

describe laminar flow

Answer 6

thin sheets of moving air over one another, little mixing of layers with the surface air being stationary

Question 7

describe turbulent flow

Answer 7

mixing between layers, gusts and eddies, surface layer is stationary

Question 8

what causes turbulent wind flow

Answer 8

variations in surface topography or variable surface heating

Question 9

which type of air flow can entrain sand more easily

Answer 9

turbulent

Question 10

what is the reynolds number

Answer 10

it distinguishes between laminar and turbulent flow

Question 11

what wind has the highest velocity in the troposphere

Answer 11

jet stream

Question 12

what is the boundary layer

Answer 12

the layer roughly 300m in altitude in which all exchanges between surface and atmosphere take place

Question 13

describe the wind conditions of the boundary layer

Answer 13

turbulent flow, slower due to friction, dust storms will fill up within the boundary layer

Question 14

what is the roughness layer

Answer 14

2-5cm over grass or 2-5 m in forests, almost still flow

can be determined by plant height and flexibility

Question 15

what is the roughness length

Answer 15

height where the wind is effectively 0m per second

Question 16

3 forces that work together to entrain sediment in the wind

Answer 16

gravity- keep grain at surface, drag- moves grain along ground, lift- shear stress

Question 17

4 methods of aeolian sediment transport

Answer 17

suspension, creep, reptation, saltation

Question 18

describe creep

Answer 18

grain remains in contact w surface most of the time, coarser grains,

Question 19

describe reptation

Answer 19

hopping motion, transitional between creep and saltation, hit other grains and cause them to bounce forward

Question 20

describe saltation

Answer 20

jumping motion, 35 degree angle, parabolic pathway, 2-4cm height, dominant transport method

Question 21

5 factors influencing sediment entrainment in aeolian systems

Answer 21

sediment size
surface vegetation
surface crusting
surface moisture
surface slope

Question 22

what is fluid threshold velocity

Answer 22

min wind speed to initiate grain movement by wind force alone

Question 23

what is impact threshold

Answer 23

min wind speed needed to initiate particle movement as a result of reptation

Question 24

what bacteria can create organic crusts

Answer 24

cyanobacteria

Question 25

what moisture content is the threshold to inhibit sediment transport

Answer 25

2-5%

Question 26

what is the effect of fog on entrainment

Answer 26

can reduce ability of wind to cause entrainment

Question 27

name the 2 sides of a dune

Answer 27

windward slope and slip face

Question 28

which dune side is steepest

Answer 28

slip face

Question 29

which slope is easier to erode

Answer 29

downslope- decreased critical threshold

Question 30

impact of surface veg on entrainment

Answer 30

surface roughness length due to plants slows velocity- plant height and flexibility

Question 31

what 2 main factors make up sediment movement

Answer 31

erosivity (power of wind) and erodibility (grain characteristics holding particles in place)

Question 32

what is deflation

Answer 32

aeolian erosion: wind causes the lifting and transport of lighter particles from dry soil

Question 33

what feature can show the predominant wind direction of the past or present

Answer 33

lunettes: dust plume deposits formed from the wind moving material away from lake hollows

Question 34

formation of desert pavements

Answer 34

wind picks up finer materials through deflation and leaves behind lag deposit-> stony pavement becomes a protective layer

Question 35

3 controls on wind erosion

Answer 35

susceptible surfaces, sufficient wind energy, removal from site of eroded material

Question 36

what is abrasion

Answer 36

erosion by suspended sand particles (transfer of kinetic energy)

Question 37

what is a ventifact

Answer 37

a rock sculptd by wind-borne particles (worn, faceted, cut or polished by these particles)

Question 38

what is the facet of a ventifact

Answer 38

a curved or flat surface cut by the wind into a ventifact

Question 39

what is a keel on a ventifact

Answer 39

sharp edge or ridge between the lee and windward side of a ventifact

Question 40

what is the difference between flutes and grooves

Answer 40

grooves open through while flutes are closed at each end

Question 41

when did most abrasion on rocks seen today occur

Answer 41

last glacial maximum with v high winds and lots of dust

Question 42

what are pedestal rocks

Answer 42

shaped like a mushroom, undercut by wind abrasion/ enhanced chemical weathering at the base

Question 43

what are yardangs

Answer 43

long ridges of resistant rock jutting out of the landscape due to the erosion of less resistant rock first
micro-yardangs can form on top
meso-yardangs are smaller and more assymmetrical, have a flat steep side and sloping downwind side