Sand Dunes Flashcards
Formation: Dunes have a downwards ‘lee’ slope and
An upwards ‘stoss’ slope.
Formation: An obstacle, such as a
Rock, allows transported particles to settle around it. The particles build up to form a dune.
Formation: The wind moves particles up the
Stoss slope by saltation. The particles accumulate on the lee slope.
Formation: As material becomes unstable,
It moves down the lee slope, resulting in dune migration downwind.
Scale: Greater dune height =
Slower movement.
Scale: Taller dune =
Greater volume.
Scale: Ripples - usually measured in
cm to 10’s of cm.
Scale: Ripples - Wind blows on
Sand crest, ripple crests are perpendicular to wind direction.
Scale: Ripples - Wavelength of ripples is
Determined by the average distance sand particles jump during saltation.
Scale: Dunes - Wavelengths measured in
10’s - 100’s metres.
Scale: Dunes - Height measured in
Metres.
Scale: Dunes -
Accumulation of sand, blown into a mound by the wind.
Scale: Draas - Large dunes, measured in
Kilometres.
Scale: Draas - Height measured in
Metres.
Form: Crescentric dunes - (3)
Crescent shaped.
Segment is wider than it is long.
In areas with a single wind direction.
Form: Crescentric dunes - Barchan dunes -
Crescents with horns pointing downwind.
Form: Crescentric dunes - Transverse - (3)
Asymmetric ridges, transverse to wind direction.
1-30 m high.
Move faster than any other dune type.
Form: The shape &
Relative position of slip faces.
Form: Linear dunes (Seif dunes) - (4)
Slip faces occur on both sides.
Can be 100m high and 100km long.
In areas with two wind directions.
Long, straight sand ridges.
Form: Star dunes - (4)
Can be over 100m high.
Wind blows from all directions.
Base resembles a star.
Isolated hills.
Form: Parabolic dunes - (4)
Wind of single direction.
Some vegetation.
Open end of U points upwind.
U-shaped.
Form: Reversing dunes - (2)
Asymmetric ridge.
Winds are balanced from opposite directions.
Complexity: Simple dunes - (3)
Basic forms.
Minimal number of slip faces.
Wind regime and intensity hasn’t changed since formation.
Complexity: Compound dunes - (2)
Large dunes with smaller dunes superimposed.
Wind hasn’t changed direction, but has decreased in intensity.
