Chapter 13: Deserts and Wind Action

How does wind differ from water? (Hint: Two methods)

1. Air is less dense than water and can erode only fine sediment 2. Wind is not confined to channels and wind can have widespread effects over vast areas.

List the two potential causes of desert pavement

1. As lag deposits, left behind as strong winds blow away the fine grains 2. By cycles of wet and dry periods causing the soil to swell and shrink raising the pebbles to the surface.

List the four characteristics of sand dune formation and draw a respective diagram.

1. Asymmetrical in cross section 2. Gentle slope facing the wind 3. Steep slope on downwind side called the slip face 4. Angle of repose for loose, dry sand is about 34 degrees.

What are the four types of sand dunes?

1. Barchan 2. Transverse 3. Parabolic 4. Longitudinal

What are two distinct landscapes in the desert southwest?

1. Colorado Plateau 2. Basin and Range province

Define the following terms monocline, hogback, and cuestas found in the Colorado Plateau?

Monocline: A step-like fold in rock layers. Hogback: Steeply titled resistant layer Cuestas: Gently titled resistant layer with one steep side.

What areas can be associated with deserts? (Hint: Air)

Most deserts are associated with areas with descending air.

Describe some features of the Colorado Plateau?

Mostly flat lying beds, 1500 m. above sea level (well exposed in the Grand Canyon) eroded into Plateaus, Mesas and Buttes

Define the term sand dune

Mounds of loose sand piled up by the wind

What two factors lead to strong winds in desert regions?

Large daily temperature and pressure differences

Within the basin and Range province, what happens to deposited sediment, and define the term bajada.

Sediment gets deposited into alluvial fans, sloping piles that fan outward from the mouths of mountain canyons - - --Coalesced fans (bajada)

In terms of characteristics of deserts, how do streambeds flow, and what do they cause?

Streambeds flow intermittently, typically during/after heavy rains, causing flash floods - Typically desert streambeds are usually dry.

Define the term saltation in terms of wind.

Wind can keep dust in suspension, but larger sand grains move by hopping along the ground

Fill in the blank. __is an important agent of ___ of ___ in desert regions

Wind is an important agent of erosion and transportation in desert regions

Define the term blowout that is caused by deflation

A depression on the land surface caused by wind

Define the term pediment.

A gently sloping erosional surface cut into the solid rock of an eroding mountain range; usually covered with a thin veneer of sediment.

Define the term butte.

A narrow hill of resistant rock with a flat top and very steep sides

Define the term playas.

A very flat surface underlain by hard, mud-cracked clay, a dry lakebed.

What are blocks of rock that form mountain ranges bounded by?

Faults

Define the term longitudinal dune and draw a diagram.

Form in areas with large sand supply, parallel to the prevailing wind direction - the largest type of dune

In a desert climate, what does lack of water result in terms of what types of rock form, how resistant are they, and what forms do they take?

Igneous, limestone, and metamorphic rock that are resistant to weathering and erosion and stick out as cliff and ridge forming rocks?

Define the term deflation

The removal of clay, silt and sand particles from the land surface

Define the term barchan dune and draw a diagram.

Crescent-shaped sand dune with horns that point downwind and a steep slip face on the concave side

Are all deserts hot? Explain the reasoning behind your answer and give an example location.

No; polar deserts develop in areas where cold descending air interacts with arid climate with snow and ice cover. - Ex: Antarctica.

Define the term transverse dune and draw a diagram.

Relatively straight, elongate dunes oriented perpendicular to the wind direction

Define the term ventifacts

Rocks with wind-abraded surfaces

What is the Basin and Range province characterized by?

Rugged, linear, and fault-bounded mountain ranges separated by flat valley floors

What is the predominant force that shapes most desert landscapes?

Running water despite low rainfall (rare flash floods produce most of water erosion in deserts)

Fill in the blank Sand dunes generally develop in areas with ___ and ____

Sand dunes generally develop in areas with large sand supply and winds that generally blow in the same direction.

Fill in the blank ___ moving in __ can effectively ___ into erosional forms called ___

Sand grains moving in high-speed winds can effectively sand-blast rocks into erosional forms called ventifacts.

With the distribution of deserts, write four factors that determine where some develop with respect to location?

1. Location of most deserts related to descending air. 2. Some related to rain shadow 3. Some develop due to great distance from ocean. 4. Some develop on tropical coasts next to cold ocean currents

Different types of sand dunes form depending on what three type of factors?

1. The amount of sand available 2. The wind's velocity and constant direction 3. Arrangement of any vegetation cover.

Define the term mesa

A broad, flat-topped hill bounded by cliffs and capped by a resistant rock layer

Define the term rain shadow and draw a diagram.

A region on the downwind side of mountains that has little or no rain because of the loss of moisture on the upwind side.

Define the term desert pavement

A thin, surface layer of closely packed pebbles.

Describe the relationship between alluvial fans, bajadas, and playas (hint: talk about type of sediment)

Alluvial fans may or may not overlap to form bajadas. Finest sediments travel to center of basin where water ponds evaporates into playas.

Define the term desert.

Any region with an arid climate that receives less than 25cm of precipitation per year

Describe how a pediment forms and draw a diagram of the formation.

As the mountain front erodes, it retreats uphill, maintaining a constant slope on the mountain front and the pediment. Eventually, only residual hills remain.

Define the term barchanoid ridges

Barchan dunes that join together and if the ridges become straight enough they form into transverse dunes.

Define the term plateau and what forms it?

Broad, flat-topped areas elevated above the surrounding land that form as a result of flat lying beds.

Define the term parabolic dune and draw a diagram.

Deeply curved, look similar to barchans, but are convex in the downwind direction and form around blowouts in areas with abundant sand, with horns that point upwind which are typically anchored by vegetation

Define the term loess

Deposit of wind-blown silt and clay composed of unweathered, angular grains of quartz, feldspar and other minerals (glacial rock flour) weakly cemented by calcite

Define the term arroyos. What are they the result of?

Desert washes that are steep sided with flat floors covered by loose sediment. Formed as the result of rare but highly erosive flash floods.

In a desert climate, what is the type of rock that is the least resistant to erosion?

Shale and mudstone are the least resistant rock in the desert.