why wind becomes an effective geomorphic agent in the desert?
Wind blankets the
sandy deserts and strips hundreds of the
millions of tonne of dust each year.It was more effective in the
past(example:-Mesozoic era) than today.wind is more effective indeserts in the
wetter environments not because it blows with greater strength in the former
than in the latter but due to the separate reasons:-
a)Dry surfaces;&
b)sparse
vegetation.
a)Dry surfaces:-
moisture and
mobility-
when the interstitial spaces between particle pores are saturated,loose surface
particles are partially exposed to the drag and lift forces of the wind.Surace cohesion holds the
particles tightly which is maximum when the meniscues are tightly curved out and they extend over maximu grain surface .drying breaks
meniscuses and cohesion teminates making surface particles more
and more vulnerable to drag and lift forces of the wind.moisture increases threshold of movement.rule-of
thumb estimates choose 4% water content as limit to wind erodibility
although Goldsmith et al found that there was no erodibilty at
1.8% soil moisture by weight.discrepencies like this occur due to difference in
content of organic matter,fine particles
or algae and bacteria,pattern of rainfall and sand moving wind also influences erodibility.thus,soil
moisture constraint in the desert strengthen wind's geomorphic effectiveness in
the desert.
b)sparse
vegetation:-
The shallow layer
above the plant has zero wind velocity and is called roughness height which
varies with the plant height,vegetative characteristics,density of plant cover
and plant litter in agricultural fields and in the semi-arid areas.wind
permeable ,gramminiform and erect and spreading
palnts are less efective in checking particle movement than the
squatter,dense plants .Moving sand and soil moisture constraint makes plants to grow in a egion where the
rooting media is not largely mobile resulting in sparese vegetation leaving
large area for the wind to carry and particles.
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