Sand Dunes

Question 0

Formation: Dunes have a downwards ‘lee’ slope and

Answer 0

An upwards ‘stoss’ slope.

Question 1

Formation: An obstacle, such as a

Answer 1

Rock, allows transported particles to settle around it. The particles build up to form a dune.

Question 2

Formation: The wind moves particles up the

Answer 2

Stoss slope by saltation. The particles accumulate on the lee slope.

Question 3

Formation: As material becomes unstable,

Answer 3

It moves down the lee slope, resulting in dune migration downwind.

Question 4

Scale: Greater dune height =

Answer 4

Slower movement.

Question 5

Scale: Taller dune =

Answer 5

Greater volume.

Question 6

Scale: Ripples - usually measured in

Answer 6

cm to 10’s of cm.

Question 7

Scale: Ripples - Wind blows on

Answer 7

Sand crest, ripple crests are perpendicular to wind direction.

Question 8

Scale: Ripples - Wavelength of ripples is

Answer 8

Determined by the average distance sand particles jump during saltation.

Question 9

Scale: Dunes - Wavelengths measured in

Answer 9

10’s - 100’s metres.

Question 10

Scale: Dunes - Height measured in

Answer 10

Metres.

Question 11

Scale: Dunes -

Answer 11

Accumulation of sand, blown into a mound by the wind.

Question 12

Scale: Draas - Large dunes, measured in

Answer 12

Kilometres.

Question 13

Scale: Draas - Height measured in

Answer 13

Metres.

Question 14

Form: Crescentric dunes - (3)

Answer 14

Crescent shaped.
Segment is wider than it is long.
In areas with a single wind direction.

Question 15

Form: Crescentric dunes - Barchan dunes -

Answer 15

Crescents with horns pointing downwind.

Question 16

Form: Crescentric dunes - Transverse - (3)

Answer 16

Asymmetric ridges, transverse to wind direction.
1-30 m high.
Move faster than any other dune type.

Question 17

Form: The shape &

Answer 17

Relative position of slip faces.

Question 18

Form: Linear dunes (Seif dunes) - (4)

Answer 18

Slip faces occur on both sides.
Can be 100m high and 100km long.
In areas with two wind directions.
Long, straight sand ridges.

Question 19

Form: Star dunes - (4)

Answer 19

Can be over 100m high.
Wind blows from all directions.
Base resembles a star.
Isolated hills.

Question 20

Form: Parabolic dunes - (4)

Answer 20

Wind of single direction.
Some vegetation.
Open end of U points upwind.
U-shaped.

Question 21

Form: Reversing dunes - (2)

Answer 21

Asymmetric ridge.

Winds are balanced from opposite directions.

Question 22

Complexity: Simple dunes - (3)

Answer 22

Basic forms.
Minimal number of slip faces.
Wind regime and intensity hasn’t changed since formation.

Question 23

Complexity: Compound dunes - (2)

Answer 23

Large dunes with smaller dunes superimposed.

Wind hasn’t changed direction, but has decreased in intensity.

Question 24

Complexity: Complex dunes - (2)

Answer 24

Large dunes with smaller dunes of different type superimposed.
Significant change in wind direction and intensity.