21 DESERTS AND WIND A desert is a region that receives less than 25 cm of precipitation per year What is the annual precipitation in your region Life Support Vegetation is so sparse and water so rare that a desert is unable to support significant populations of animals ID: 271710
Download Presentation The PPT/PDF document "CHAPTER" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
Slide1
CHAPTER
21:
DESERTS AND WINDSlide2
A desert is a
region that receives less than 25 cm of precipitation per year.
What is the annual precipitation in your region?Slide3
Life Support
Vegetation is so sparse, and water so rare, that a desert is unable to support significant populations of animals.Slide4
Temperature
Desert regions can have extreme temperatures ranges because the
atmosphere contains little humidity to block the Sun's rays or retain heat at night.Slide5
Natural Climate Change
Climates can change naturally. The Sahara region was humid 5,000 to 10,000 years agoSlide6
Deserts may be hot or cold, but low precipitation is a common traitSlide7
Arctic circle
Some would argue that the “Arctic Desert” isn’t really a desert. Why do most cool dry areas have more vegetation than hot dry areas?Slide8
Atmospheric moisture circulation determines
the location of most deserts
Polar Cells
Ferrel CellsHadley CellsSlide9
Formation
Air warms and contracts as it sinks closer to Earth’s surface.
Evaporation
exceeds condensation.Deserts form, clustered around 30°N and 30°S latitudes.Slide10
Other Factors Determining Desert Formation
Not all deserts lie around 30° latitude
Several
other factors contribute to desert locations:• orographic effectSlide11
Other
Factors Determining Desert Formation
dry, cold air descending over polar regionsthe
distance atmospheric moisture is transported Slide12
Other Factors Determining Desert Formation
cold
ocean current adjacent to a tropical coastSlide13
Other Factors Determining Desert Formation
poor
management of farmlandSlide14
Other Factors Determining Desert Formation
deforestationSlide15
Each desert has unique characteristics
Trade Wind DesertsSlide16
Each desert has unique characteristics
Mid-latitude DesertsSlide17
Each desert has unique characteristics
Rain Shadow DesertsSlide18
Coastal desertsSlide19
Ripple and dune Terminology
Wind is an important geological agentSlide20
Ripple and dune Terminology
Suspension: Silt
carried in suspension produces well-sorted deposits of progressively smaller sediments with distance.Slide21
Ripple and dune Terminology
Loess:
Eolian deposits of silt are left by continental glaciations
Mineralogically
how does loess differ from typical wind-blown sand?Slide22
Ripple and dune Terminology
Desert Pavement
(lag deposit of coarse sediment left after fines blow away)
Yardang (rock outcrop sculpted by sand abrasion)Slide23
Sand Dunes reflect sediment availability and
dominant wind direction
Abundant loose sediment (usually sand)
Energy to move sediment (usually wind)An obstacle to trap sand (often a bush)A dry climateSlide24
Ripple and dune Terminology
Barchan
(
Crescentic
Dune)
Strong
wind in one
direction, small
amounts of
sand, limited vegetation
Transverse (
Crescentic
Dune)
Weak wind in one
direction, large
amounts of
sand deposited
perpendicular to
wind, limited
vegetationSlide25
Ripple and dune Terminology
Parabolic Dune
Arms stabilized upwind by vegetation,
often
start as semi-circular blowouts that
elongate
Longitudinal
Dune
Winds
flowing in opposing directions,
two
slip faces, aligned with
windSlide26
Ripple and dune Terminology
Star dune
Multidirectional
winds, largest
dunes,
grow
tall instead of
moving
Sand
seas
Large regions (>125 km
2
)
of
windblown
sand numerous
, very large
dunes, sand
covers >20% of the ground surfaceSlide27
Sand Dunes
What are the differences in shape and wind characteristics of
Barchan
and Parabolic dunes?Slide28
Arid Landforms
Arid landforms can be shaped by
waterFlash floods are commonStreams tend to be ephemeral, flowing only after heavy rain. Slide29Slide30
Evolution
of Desert LandscapesSlide31
Playa Lakes
Playa Lakes are products of rainfall and evaporation
What is the evidence that this area was recently wet?Slide32
Desertification
Desertification is the process by which land loses its vegetation and turns into a desert
Both natural and anthropogenic factors lead to desertification. What are some of the factors?Slide33
Environmental refugeesSlide34
Desertification
Desertification
threatens all six inhabited continentsSlide35
COPYRIGHT
Copyright © 2014 John Wiley & Sons Canada, Ltd. All rights reserved. Reproduction or translation of this work beyond that permitted by Access Copyright (The Canadian Copyright Licensing Agency) is unlawful. Requests for further information should be addressed to the Permissions Department, John Wiley & Sons Canada, Ltd. The purchaser may make back-up copies for his or her own use only and not for distribution or resale. The author and the publisher assume no responsibility for errors, omissions, or damages caused by the use of these programs or from the use of the information contained herein.