Wind erosion in drylands - Arid Zone Geomorphology - page 550

wind storms. Numerous authors have observed that where
wind flow is strictly unidirectional, the lee side of a boul-
der is unabraded (Blackwelder, 1929; McKenna Neuman
and Gilbert, 1986).

arid states are changes in the supply of abrasive sedi-
ment, the nature of depositional processes (e.g. infilling
of basins by lacustrine sediments), the height of the wa-
ter table (which forms the base level for wind erosion),
the biomass of vegetation and the strength and frequency
of winds. During wetter phases, aeolian erosion probably
ceases in all but the most favourable locales. Nonetheless,
the interplay of wet and dry climates is probably essential
for the nature and continuity of aeolian processes as we
know them.

21.3 Conclusions

Landscapes of aeolian erosion are seldom produced by
the wind alone, although it may be the dominant player.
Yardangs and desert depressions (discussed in Chapter 15)
evolve through a host of interacting processes, including
those that are both endogenic (tectonic) and exogenic (so-
lutional weathering, abrasion, deflation, fluvial erosion
and mass movement of different types). Ventifacts are
the sole form developed almost exclusively by wind ero-
sion and, more specifically, by abrasion. However, even
for ventifacts it must be recognised that weathering as-
sociated with climate change can play a role, by either
softening or hardening the surface, thereby affecting the
nature and rate of abrasion.
Although each aeolian landform is commonly reviewed
and discussed in isolation, they are often part of a larger
landscape of aeolian activity, most notably in extremely
arid regions where sand flows across vast regions to form
a suite of landforms. The transported sands have a strong
corrasive effect on outcropping rocks, moulding them into
basins, yardangs and ventifacts and, at times, creating in-
verted relief as they pass over ancient 'hardened' drainage
systems.
Improved access to remote sensing imagery has pro-
vided a greater understanding of the landscape patterns of
aeolian erosion, suggesting complicated assemblages of
natural interactions within aeolian systems as a whole.
Studies of tectonics, sand transport and dust emission
have added new insights to our understanding of many
of the large-scale processes involved. It remains to ex-
amine the spatial distribution of erosion and deposition
within a broader context of the role of topography on
the flow field, the distribution of shear stress, the effect
of changing material type and the pathways of sediment
transport.
A review of modern global wind erosion suggests that
it reaches its greatest intensity and extent in hyper-arid
regions. In more humid settings, such as the deserts of the
American southwest or Australia, wind erosion is much
more localised in its occurrence. Our understanding of
contemporary processes helps us to consider the role of
climate change in fashioning desert environments. Re-
search conducted over the past few decades hints at the
importance of such fluctuations to aeolian landscapes. As-

References

Alavi Panah, S.K., Komaki, Ch. B., Goorabi, A. and Matin-
far, H.R. (2007) Characterizing land cover types and surface
conditions of yardang region in Lut Desert (Iran) based upon
Landsat satellite images. World Applied Sciences Journal , 2 ,
212-228.
Al-Dousari, A.M., Al-Elaj, M., Al-Enezi, E. and Al-Shareeda,
A. (2009) Origin and characteristics of yardangs in the
Um Al-Riman depressions (N Kuwait). Geomorphology , 24 ,
93-104.
Anderson, R.S. (1986) Erosion profiles due to particles en-
trained by wind: application of an aeolian sediment-transport
model. Bulletin of the Geological Society of America , 97 ,
1270-1278.
Bailey, J.E., Self, S., Wooller, L.K. and Mouginis-Mark, P.J.
(2007) Discrimination of fluvial and eolian featues on large
ignimbrite sheets around La Pacana Caldera, Chile, using
Landsat and SRTM-derived DEM. Remote Sensing of Envi-
ronment , 108 , 24-41.
Banks, M., Bridges, N.T. and Benzit, M. (2005) Measurements
of the coefficient of restitution of quartz sand on basalt: im-
plications for abrasion rates on Earth and Mars. Lunar and
Planetary Science , XXXVI , 2116.
Beresford-Jones, D., Lewis, H. and Boreham, S. (2009) Linking
cultural and environmental change in Peruvian prehistory:
Geomorphological survey of the Samaca Basin, Lower Ica
Valley, Peru. Catena , 78 , 234-249.
Blackwelder, E. (1929) Sandblast action in relation to the
glaciers of the Sierra Nevada. Journal of Geology , 37 ,
256-260.
Blackwelder, E. (1934) Yardangs. Bulletin of the Geological
Society of America , 45 , 159-165.
Bobek, H. (1969) Z ur Kenntnis der S udlichen Lut. Mitteilun-
gen der Osterreicher Geographischen Gesellschaft, Wien , 3 ,
155-192.
Bosworth, T.O. (1922) Geology of the Tertiary and Quaternary
Periods in the North-west Part of Peru , Macmillan and Com-
pany, London.
Bowen, A.J. and Lindley, D. (1977) A wind-tunnel investigation
of the wind speed and turbulence characteristics close to
the ground over various escarpment shapes. Boundary-Layer