1. Deserts
Bob Leighty
GLG Physical Geology

2. These notes and web links are your primary “lecture” content in this class. Additionally, various articles are assigned each week to supplement this “lecture” information. I believe you’ll have enough information to reference without having to purchase a costly textbook.
These lecture notes are very similar to the ones I use in my traditional classes. You’ll find they are loaded with imagery and streamlined text that highlight the most essential terms and concepts. The notes provide a framework for learning and, by themselves, are not meant to be a comprehensive source of information.
To take advantage of the global knowledge base known as the Internet, I have included numerous hyperlinks to external web sites (like the Wikipedia, USGS, NASA, etc.). Follow the links and scan them for relevant info. The information from linked web sites is meant to supplement and reinforce the lecture notes – you won’t be responsible for knowing everything contained in them.
As a distance learning student, you need to explore and understand the content more independently than in a traditional class. As always, I will help guide you through this learning adventure. Remember, Dr. Bob if you have any questions about today’s lecture
Leave no questions behind!
Explore and have fun!

3. There’s only one “S” in Desert
Deserts
There’s only one “S” in Desert
Desert
Dessert

4. Desert Misconceptions
Deserts
Desert Misconceptions
Deserts are giant seas of sand

5. Desert Misconceptions
Deserts
Desert Misconceptions
Deserts are giant seas of sand
> No way! Some are sandy, rocky, even icy!

6. Desert Misconceptions
Deserts
Desert Misconceptions
Deserts are always hot

7. Desert Misconceptions
Deserts
Desert Misconceptions
Deserts are always hot
> Untrue! Some are numbingly cold!

8. Desert Misconceptions
Deserts
Desert Misconceptions
Deserts are lifeless

9. Desert Misconceptions
Deserts
Desert Misconceptions
Deserts are lifeless
> Think again, bucko! Deserts can be teeming with life, …

10. Desert Misconceptions
Deserts
Deserts are lifeless
> Think again, bucko! Deserts can be teeming with life, …
…especially on other planets!

11. WWW What is a Desert? An arid region that gets <10” of rain/year
Deserts
What is a Desert?
WWW
An arid region that gets <10” of rain/year
Can be hot (Sahara) or cold (Patagonia)
Semi-arid regions get 10-20” of rain/year
May have lots of sand, a little sand, or rocky
Generally lacks significant vegetation
Deserts cover roughly 1/3 of the Earth’s land surface

12. Deserts
Why Do Deserts Form?
The amount of annual precipitation defines arid regions (deserts)
Deserts usually form from a combination of factors:
1) Global air convection patterns
> Equator – Rising warm, moist air (low-pressure)
> Lower latitudes (10-30 N & S) – Dry air descends & warms and compresses air underneath (high-pressure)
* This controls the location of many deserts

13. Deserts
Why Do Deserts Form?
Weather map symbols: H = descending high-pressure air, L = rising low-pressure air

14. Why Do Deserts Form? Many deserts form from a combination of factors:
2) Geography
> Regional elevation, proximity to mountain ranges & cold ocean currents, etc.
* This can be an important influence on regional climate

15. Deserts of the southwestern USA
Sonoran Desert – A mid-latitude desert GB M S C
Other SW USA deserts - Great Basin, Mojave, Chihuahuan, etc.

16. Deserts of the southwestern USA
Arizona is mostly arid & semi-arid

17. Subtropical (Trade wind or Mid-Latitude)
Deserts
Types of Deserts
Subtropical (Trade wind or Mid-Latitude)
Between 10-30 N & S of the Equator
Examples: Sahara, Rub al Khali

18. Subtropical (Trade wind or Mid-Latitude)
Deserts
Types of Deserts
Subtropical (Trade wind or Mid-Latitude)
Commonly occur within continents
Examples – Sonoran, Gobi, Australian

19. Types of Deserts Rain Shadow
Large mountain ranges block air flow and create a rain shadow
1) Air rises & cools 2) condensation & precipitation 3) dry air descends & heats up

20. Types of Deserts Rain Shadow Deserts form behind major mountain ranges
Examples: Great Basin (Sierra Nevada), Chihuahuan (Sierra Madre), Patagonian (Andes)

21. Types of Deserts Coastal
Land adjacent to cold ocean currents (dry air)
Atacama (<1 cm/yr - from fog)
Examples: Atacama (South America), Namib (South Africa)

22. Deserts
Types of Deserts
Polar
High north & south latitudes (cold) near the poles
Air is way too cold to hold much water
Examples: Greenland, Antarctica

23. Types of Deserts Paleo Desert areas of the geological past
Example: Coconino Sandstone (Paleozoic), Navajo Sandstone (Mesozoic)

24. Types of Deserts Extraterrestrial Desert areas on other worlds
Example: Mars

25. Desert Landforms Normal faulting creates basins & ranges
Deserts
Desert Landforms
Normal faulting creates basins & ranges
Erosion of mountains, deposition in basins

26. Desert Landforms Inselbergs, alluvial fans, bajadas, playas, etc.
Deserts
Inselbergs, alluvial fans, bajadas, playas, etc.

27. WWW Eolian Processes Erosion
Deserts
WWW
Erosion
Eolian (wind) abrasion (“sand-blasting”) produces ventifacts, yardangs, balanced rocks, etc.
ventifacts
balanced rocks

28. Eolian Processes Transportation
Deserts
Eolian Processes
Transportation
Wind typically can’t pick-up particles larger than sand
Mostly silt and dust (suspended load)

29. Eolian Processes
Deserts
WWW
Deposition
Sand dunes, ripples, etc.

30. WWW Desert Pavement Thin, pebble-rich layer
Deserts
Desert Pavement
WWW
Thin, pebble-rich layer
Formed by a) wetting & drying OR b) deflation

31. WWW Desert Varnish Dark outer coating of Fe & Mn oxides + clay
Deserts
Desert Varnish
WWW
Dark outer coating of Fe & Mn oxides + clay
Formed by chemical? or biologic processes?

32. WWW Links in this Lecture
Deserts
> Deserts -
> Sonoran Desert -
> Great Basin -
> Mojave Desert -
> Chihuahuan Desert -
> Sahara -
> Rub al Khali -
> Gobi Desert -
> Australian Deserts -
> Rain shadow -
> Sierra Nevada -
> Sierra Madre -
> Patagonian Desert -
> Andes -
> Atacama Desert -
> Namib Desert -

33. WWW Links in this Lecture
Deserts
> Inselberg -
> Alluvial fan -
> Playa -
> Eolian processes -
> Ventifact -
> Yardang -
> Sand dunes -
> Desert pavement -
> Desert varnish -