A view overlooking Death Valley, California'

1

• A view overlooking Death Valley, California.

Fig. 14-CO, p.333
2

• Why do deserts exist?
• Falling air creates deserts at 30 degrees north
  and south latitudes. The red arrows inside the
  globe show surface winds the blue arrows (right)
  show air flow on the surface and at higher
  elevations.

Fig. 14-1, p.335
3

• The major deserts of the world. Where are they
  concentrated?
• Deserts cover 25 of the Earths land surface
  where 13 of the worlds population lives. A
  desert is any region that receives less than
  _______ inches of rain per year.

Fig. 14-2, p.335
4

• Rain-shadow deserts form where warm, moist air
  from the ocean rises as it flows over mountains.
  As it rises, it cools and water vapor condenses
  to form rain. The dry descending air on the lee
  side absorbs moisture, forming a desert.

Fig. 14-3, p.335
5

• Rainfall patterns in the State of California,
  where prevailing winds carry moist Pacific air
  eastward over the mountains. Note that
  rain-shadow deserts lie east of the mountain
  ranges.
• What about the Atacama and Gobi deserts?
• Rainfall given in cm/year.

Fig. 14-4, p.336
6

• Water and Deserts. Water reaches the desert from
  three sources streams (from wetter regions),
  groundwater and rain/snowfall. The Colorado
  River (above) flows from the Rockies through the
  arid SW United States and empties (where?).

Fig. 14-5, p.337
7

• Desert Streams Courthouse Wash, Utah. In the
  spring, when rain and melting snow fill the
  channel with water

Fig. 14-6a, p.337
8

• same wash, in the summer, when the creek bed is
  dry
• A stream bed that is dry for most of the year is
  called a wash (or arroyo)
• where does the water go? what is a water table
  and where is it in this photo?

Fig. 14-6b, p.337
9

• Desert Lakes
• Mud cracks pattern the floor of a playa in Utah.
• An intermittent desert lake is called a playahow
  does it form?
• Is the Salton Sea a playa lake?

Fig. 14-7, p.338
10

• When lakes evaporate, ions precipitate to deposit
  salts on the playa. Economically valuable
  mineral deposits can accumulate over the years.
  Here, a mule team is hauling valuable mineral
  deposits from Death Valley during the 1800s.

Fig. 14-8, p.338
11

• Flash Floods
• In August 1997, 11 hikers perished when a flash
  flood filled a slot canyon similar to this one in
  the Utah desert. The steep walls made escape
  impossible.

Fig. 14-9, p.338
12

• Pediments and Bajadas An alluvial fan in Death
  Valley forms where a steep mountain stream
  deposits sediment where is enters a valley. A
  Bajada is a depositional surface.

Fig. 14-10, p.339
13

• The Bajada in the foreground merges with a gently
  sloping pediment to form a continuous surface in
  front of mountains in Mongolia. The basin has no
  external drainage. A pediment is an erosional
  surface where sediment is transported from the
  mountains to the bajada.

Fig. 14-11, p.339
14

• Two American Deserts The Colorado Plateau
  Death Valley and the Great Basin
• Features of the Colorado Plateau include spires
  and buttes formed when streams reach a temporary
  base level and erode laterally. The streams
  transport the eroded sediment away from the
  region. Bottom photo is spires and buttes in
  Monument Valley, Az. A plateau is a large
  elevated area of fairly flat land. It is a
  larger area than mesas and buttes.

Fig. 14-12, p.340
15

• Location of Great Basin shown in redColorado
  Plateau is to the right of the great basin and
  takes in parts of Utah, Colorado, Arizona and New
  Mexico.

Fig. 14-13b, p.341
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Fig. 14-12a, p.340
17
Fig. 14-12b, p.340
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• Death Valley and the Great Basin sediment eroded
  from surrounding mountains is slowly filling
  Death Valley, in the rain shadow of the Sierra
  Nevadas. DV has no external drainage, unlike the
  Colorado Plateau which drains to the Gulf of
  California.

Fig. 14-13, p.341
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Fig. 14-13a, p.341
20

• Bajadas and pediments are common features of the
  Great Basin. The form from a combination of
  tectonic, erosional and depositional processes.
  Mountains a valleys commonly form by block
  faulting (horst and graben or basin and range
  topography). Mountains slowly drown in their own
  sediment

Fig. 14-14, p.341
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Fig. 14-14a, p.341
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Fig. 14-14b, p.341
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Fig. 14-14c, p.341
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• Wind it blows across and erodes bare,
  unprotected desert soil and forms features such
  as dunes, desert pavement and loess.
• To right, wind erodes silt and sand (called
  deflation) but leaves larger rocks behind to form
  desert pavement. This is a continuous cover of
  stones that protects the desert surface from
  further erosion.

Fig. 14-15, p.342
25
Fig. 14-15a, p.342
26
Fig. 14-15b, p.342
27

• Wind also moves sand grains by saltation (usually
  not lifted more than 1 meter off the ground)
  which can carve features by abrasion such as the
  pinnacle to right in the Grand Canyon.

Fig. 14-16, p.343
28

• Dunes a mound or ridge of wind-deposited sand.
  They form when wind erodes sand from one location
  and deposits it in another.
• To right, dunes near Lago Poopo, Bolivia.

Fig. 14-17, p.343
29

• Blowouts can form (saucer or trough-shaped
  depression). They can very large, such as the
  Qattara Depression in Egypt (100 meters deep, 10
  km in diameter).

Fig. 14-18, p.343
30

• Most dunes are assymetrical wind erodes sand
  from the windward side of a dune, carries it up
  to the dune crest and the sand slides down on the
  sheltered leeward side (slip face) at the angle
  of repose for sand (approx. 35 degrees).

Fig. 14-19, p.343
31

• Whats this? When dunes become buried by younger
  sediment and lithified over geologic time, the
  sandstone retains the original sedimentary
  structures of the dunes. Steeply dipping layers
  of the dune face are preserved here as
  cross-bedding (Zion National Park).

Fig. 14-20, p.344
32

• Types of Dunes When sand supply is limited
  (rocky deserts), the tips of Barchan dunes travel
  faster than the center and point downwind.
  Barchans migrate independently.

Fig. 14-21, p.344
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Fig. 14-21ab, p.344
34
Fig. 14-21c, p.344
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• If sand is plentiful and evenly dispersed, it
  accumulates in long ridges called transverse
  dunes aligned perpendicular to the prevailing
  wind.

Fig. 14-22, p.346
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Fig. 14-22a, p.345
37
Fig. 14-22b, p.345
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• If sparse desert vegetation is present, like
  along a seacoast or semiarid desert, a blowout
  might form at bare areas between vegetation as
  sand is eroded while the tips are anchored by
  plants surrounding the blowout. A parabolic dune
  is similar to a barchan, except that the tips of
  a parabolic dune point into the wind.

Fig. 14-23, p.346
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Fig. 14-23a, p.346
40
Fig. 14-23b, p.345
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• If the wind direction is erratic but prevails
  from the same general compass direction and sand
  supply is limited, then long, straight
  longitudinal dunes form parallel to the
  prevailing wind direction. In the Sahara Desert,
  they can reach 100 km long.

Fig. 14-24, p.346
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Fig. 14-24a, p.346
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Fig. 14-24b, p.346
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• Loess wind can carry silt for hundreds or
  thousands of miles and deposit it as silt. Silt
  is porous, uniform and typically lacks layering,
  and particles can interlock. Its not cemented,
  but can form vertical cliffs and bluffs. The
  largest deposits in China, more than 300 meters
  thick, were used as dwellings. In 1920, a great
  earthquake collapsed the cave system and killed
  an estimated 100,000 people. Above are loess
  caves in Pakistan.

Fig. 14-25, p.346
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• Loess deposits in the United States. Soils
  formed on Loess are generally fertile and make
  good farmland.

Fig. 14-26, p.347
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• Desertification What is it?

Fig. 14-27, p.348
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p.349