How do you think this formed?
What are the main agents of
erosion in deserts?
 Wind
 Water
 Contrary to what we might believe, water is actually
thought to be the most significant agent of erosion at
work in desert environments
Weathering
 What is the difference between chemical and physical
weathering? Write a definition for each.
 Which is most important in a desert? (see p 290 PG)
 Why is weathering in deserts so slow?
Insolation Weathering
Insolation weathering
 Also known as exfoliation or onion skin weathering.
Why?
 Large diurnal temp range (alternate heating & cooling)
 Occurs when there is a sudden temperature change (eg
cool rainfall)
 In deserts rock temperatures of up to 80 degrees have
been recorded. Rocks may be 20 degrees hotter than
the surrounding air.
Salt Crystallisation
 Most efficient underground, where there is more
moisture
 Salt crystallisation is where rocks are broken down by
salt crystals growing in the cracks
 Salts in the soil and rock are dissolved and penetrate
porous rocks eg sandstone
 As they recrystallise they exert pressure and force the
rocks to break apart
Sand Blasting
 Entrained particles (those picked up by the wind) are
carried by the wind, and act like sandpaper on the
bottom of rocks where most sand particles are carried.
(abrasion)
 Helps to form mushroom rocks (but chemical
weathering is important too)
Solution weathering
 A form of chemical weathering, where rainwater
dissolves soluble particles in the rock.
Relic Features
 Many desert features are actually relic features from
times when there was much more water present in the
environment.
What is badland topography?
 See p 292 PG
 What is the impact of the slow rate of weathering in
arid environments on the development of landforms?
 What is the difference between weathering and
erosion?
 How does the rate of weathering affect desert erosion?
Desert Landforms
 Weathering and erosion combine to form some
significant desert landforms.
 Water and wind both play an important role in their
formation
Water and landform development
in arid environments
Make notes from p292-294 on:
 The role of water
 Rainsplash
 Exotic rivers
 Internal drainage
 Playas
 Evaporites
 Wadis/arroyos/dry creeks
 Alluvial fan
 Piedmont
 Bajada
 Box canyon
 Anabranches
 Reticulate drainage
 Inselbergs (see p 192 landform systems)
 Why is water more effective than wind at shaping
landforms in arid environments?
Wind and landform development
in arid environments.
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Make notes from p295-296 on
Aeolian action
Ergs
Deflation & deflation hollows
Saltation
Sand sheets
Barchans
Parabolic dunes
Longitudinal or seif dunes
lunettes
 Pics from
 http://www.egyptoffroad.com/trips.html
http://farm4.static.flickr.com/3017
/2707437345_befb90765c.jpg?v=0