HOME>>
DISSEMINATION
INTRO>>
ENVIRONMENTS FLORA-FAUNA DIDACTICS IMAGES GLOSSARY CREDITS
A
B
C
D
E
F
G
H
I
J
K
L
M
N
O
P
Q
R
S
T
U
V
W
X
Y
Z

Item Description
Dune
hill, mound, or ridge of sand or other loose material that is formed by wind action. The existence of dunes is a direct function of the ability of wind to transport unconsolidated material. Dunes are also associated with coasts where beach sands may be reworked by the wind. Dune sand is moved in two ways. First, by the process of saltation, the wind lifts up sand grains and carries them for a short distance before dropping them. If the sand is being blown across a stony surface, the grains may bounce up to a height of a few metres. Otherwise they move only a few centimetres above the ground surface. The second mode of movement occurs when the saltating grains hit the ground again and by the force of their impact push other grains forward. This movement is termed surface creep. The simplest way in which a dune forms is when an obstacle, be it a rock or a plant, impedes airflow and causes sand to pile up on its downwind side, rather in the way that a snowdrift forms. Gradually the dune grows, presenting even more of an obstruction to the wind-bearing sand and catching saltating grains in the leeward wind shadow.
Source: Taken from Encyclopaedia Britannica 2002

<<Back