Silt and sand

Question 1

size of coarse dust

Answer 1

20-70 microns

Question 2

size of fine dust

Answer 2

less than 20 microns

Question 3

3 sources of silt

Answer 3

from the bedrock, glacial grinding, regional sources

Question 4

name 3 regional sources of silt

Answer 4

river channels, lake basins, agri land

Question 5

what does cloudy blueish water in valleys indicate

Answer 5

high silt content due to glacial grindign

Question 6

what can indicate the weathering process that released the grain

Answer 6

study of the grain itself

Question 7

what is flocculation

Answer 7

silt particles joining together to form sand sized grains

Question 8

name 3 high yielding sources of dust

Answer 8

floodplains, playa lakes and agri land (due to ploughing practices0

Question 9

dustiest place on earth

Answer 9

Lake Chad

Question 10

how much dust transported annually in the troposphere

Answer 10

1-3 billion tons

Question 11

3 functions of dust transport

Answer 11

1. source of nutrients for rainforest system- millions of tons from Africa to the Americas
2. primary productivity of the oceans (taken in by phytoplankton)
3. radiative transfer- scatter or absorb radiation

Question 12

give two possible effects of dust on rainfall levels

Answer 12

could interfere with cloud formation by lowering the adiabatic cooling of the atmo.
OR could act as cloud condensation nuclei

Question 13

what percentage of earths surface is covered in loess

Answer 13

10%

Question 14

how is loess good for agri

Answer 14

high calcium content, fertile, moisture-holding, good for ploughing

Question 15

where is most loess derived from

Answer 15

glacial deposits

Question 16

4 sources of sand

Answer 16

weathered rock outcrops, river channels/floodplains, coastlines, lake basins

Question 17

what is the composition of a dune dependent on

Answer 17

the source of the sediment

Question 18

where is sand primarily sourced from

Answer 18

river deposition

Question 19

what is the most common mineral in sand

Answer 19

quartz

Question 20

what processes are effective at creating sand sized particles

Answer 20

fluvial and coastal movements of sediment

Question 21

example of a direct source of sand from a river basin

Answer 21

if the river basin is directly adjacent to the desert, sand can be transported by wind onto the desert

Question 22

example of an indirect source of sand from a river basin

Answer 22

river sediment dispatched into the sea which carries it by longshore drift to be blown onto the desert

Question 23

how are sand particles transported from a lake basin

Answer 23

usually clay size particles are transported, but they can be bound into sand sized particles by salt-> deposits “clay” dunes as the bonds dissolve

Question 24

how are the bright white sand of the White Sand Dunes National Monument formed

Answer 24

sourced from a playa where gypsum crystals precipitated out of the evaporating water

Question 25

what are sand sheets

Answer 25

extensive accumulation of sand in thin low relief deposits, 40% of sand seas covered by sheets

Question 26

what are zibars

Answer 26

A low-relief, rounded, coarse-grained, sand dune with no slipfaces.... usually on sand sheets

Question 27

what are sand stringers

Answer 27

focused pathways of sand transportation

Question 28

what percentage of sand seas are covered by dunes

Answer 28

60%

Question 29

what is a sand dune

Answer 29

hill or ridge of loose, well sorted sand shaped by wind and usually capable of downwind motion

Question 30

other word for the windward slope

Answer 30

stoss slope

Question 31

other words for the leeward slope

Answer 31

avalanche face, slipface

Question 32

is the leeward or windward slope usually steeper

Answer 32

leeward slope (30-43 degrees)

Question 33

up to how high can dune crests be

Answer 33

15m

Question 34

give the 5 steps of dune initiation and development

Answer 34

1. sand patch initiation 2. wind-ripple protodune 3. streamlined protodune 4. protodune 5. dune with slipface

Question 35

what is flow separation

Answer 35

the wind closest to the ground starts to lose energy and saltating sand falls to the ground

Question 36

which stage of dune development enhances flow separation to begin

Answer 36

when it is a wind-ripple protodune

Question 37

at which stage of dune development does flow separation occur

Answer 37

when it becomes a protodune

Question 38

describe how the sand dune form is maintained

Answer 38

aerodynamic control: wind increases velocity as it is pushed upwards, saltation causes sand to shoot off crest gravity control: sand falls on lee face and sis deposited

Question 39

how do dunes move

Answer 39

sand is eroded from the windward face, accumulates at the crest and avalanches down the slipface

Question 40

do larger or smaller dunes move faster

Answer 40

smaller

Question 41

what can cause a dune to become stabilised

Answer 41

vegetation

Question 42

what is sand drift

Answer 42

the process of sand movement across the desert as a result of surface winds

Question 43

what is drift potential

Answer 43

capacity of surface wind to drag sand across dry deserts

Question 44

what is resultant drift direction

Answer 44

the vector sum of drift potentials

Question 45

what is resultant drift potential

Answer 45

the amount of sand moving in the net direction

Question 46

what ratio can be used to interpret forms of dunes in a sandy desert

Answer 46

ratio of resultant drift potential to drift potential

Question 47

what is the main control on dune type

Answer 47

the wind directional variability versus the amount of sand in the dunes

Question 48

where do barchan dunes form

Answer 48

relatively sediment starved locations where there is a unimodal wind

Question 49

where do transverse/barchanoid dunes form

Answer 49

where there is a higher supply of sediment (eg from the sea) and a fairly uniform wind direction

Question 50

where do linear dunes form

Answer 50

where there are 2 wind directions (eg summer and winter) that push the sand into a ridge

Question 51

where do sand dunes form

Answer 51

where there have been multiple wind directions, arms are more mobile than core

Question 52

what are compound dunes

Answer 52

larger dunes with smaller dunes on the windward slope

Question 53

what are complex dunes

Answer 53

dunes with smaller dunes on top of a different type