1. Deserts

2. Deserts
Dry places that have a dry climate-the yearly precipitation is less than the evaporation loss
Dry regions cover 30% of the Earth’s surface
Concentrated in sub-tropics, mid-latitudes, and polar regions

3. Meteorology Principles
Warm, less dense air rises
Rising air cools
Moisture carrying capacity of air decreases
Precipitation occurs
Cold, dense air sinks (moisture depleted)
Sinking air warms
Moisture carrying capacity increases
Warm air can hold more moisture than cold air

4. Low-Latitude Deserts Types of Deserts
Along the equator is a Low pressure system, air rises
Along 30o N and S - High Pressure systems exist (Subtropical high-pressure belt, air sinks and warms
As air mass warms it can hold more moisture – any available water evaporates

5. Cold-Water Coasts Cold dry air from ocean moves over warm dry land
Land warms air mass
As air mass warms it can hold more moisture – any available water evaporates

6. Rain Shadows – Orographic Uplift
Warm, humid air masses move off of ocean
As the mass approaches a mountain it begins to rise
Rising air cools
Moisture carrying capacity decreases – precipitation occurs on the windward side
Cold, dry air mass moves over mountains and descends on the leeward side
Descending air warms and picks up moisture
Dry region is a Rain Shadow – the process is orographic uplift

7. Desert Locations

8. Weathering in Arid Climates
Mechanical Weathering is dominant
Lack of moisture and organic acids limit chemical weathering
Chemical weathering does occur, but the it takes longer

9. Water and Deserts Ephemeral streams are present in desert areas
Deserts lack vegetation
Rainfall is infrequent, but intense when it occurs
Runoff is high – get flash floods
One storm can do an enormous amount of erosion (triggering mass wasting and transporting sediment)
Water does the majority of erosional work in the deserts

10. Wind Transport of Sediment
Similar to stream transport – both air and water are fluids
Wind systems have both a bed load and suspended load
Bed Load
Primarily sands, can be gravels and
larger particles
Particles move by saltation (sands) or creep (rolling or sliding – particles larger than sand)
Causes abrasion – mechanical weathering
Suspended Load
Primarily silt with some clay
Wind has a capacity and competence

12. Wind Erosion Insignificant in erosional processes Two mechanisms
Deflation
Loose particles of sand and dust are lifted from the surface
Abrasion
Sandblasting of particles

13. Desert Pavement
Deflation occurs leaving behind coarse particles to large to carry

15. Daily Questions
Identify and appropriately place 10 characteristics in the Venn Diagram.
Wind Action
Glacial Processes
Stream Processes
Transport sediment in direction of movement
Can transport large boulders
Form dunes
Occur most frequently at high latitudes
Few associated plants and animals
Occur on at least five continents
Features formed have generally diminished in size over the last few decades
Commonly found at low elevations
More likely to occur at high elevations
Preserve a record of past climates
Characterized by the presence of snow and ice
Associated with erosion and deposition
Material is not sorted
Material is sorted
Evaporation exceeds precipitation
Cross beds form in deposits
Faster moving
Controlled by climate patterns
Involves water
Has a dissolved load
Have a competence and capacity
5 15 18
1 6 10
12 21
17 20