Chapter 13 Deserts and Wind Action

Rock debris picked up in flash floods is deposited at the base of mountains in ____.

an alluvial fan

Desert stream channels called ____ are characterized by narrow canyons with vertical walls and flat, gravel-strewn floors.

arroyos

Dunes are not just desert features, they are commonly found near ____.

beaches

A _____ is a depression on the land surface caused by wind erosion which may have a pillar left at the center.

blowout

The high runoff following sporadic desert downpours can create sudden local floods called ______.

flash floods

A ____ dune is deeply convex and its horns point upwind.

parabolic

When the desert sun dries a lake, a very flat surface underlain by hard mud-cracked clay called a _______ may form.

playa

Because sand grains are heavier than clay and silt particles, sand grains move close to the ground in a leaping pattern called ______.

saltation

This area of the desert southwest is characterized by mostly flat-lying beds of sedimentary rock over 1,500 meters above sea level.

Colorado Plateau

_______ is a thin surface layer of closely packed pebbles found in deserts.

Desert pavement

____ is a hard shiny coating of dark iron and manganese oxides and clay minerals that form on rock surfaces in arid environments.

Desert varnish

A butte is a narrow valley with a narrow bottom and flat sides.

False

A mesa is capped by sedimentary rocks while a butte is capped by a lava flow.

False

A playa lake is a deep long-lasting desert lake.

False

A transverse dune is a relatively straight, elongated dune oriented parallel to wind direction.

False

In passing over a dune, wind scours sand from the downwind or slip face.

False

Since many desert regions have internal drainage, runoff collects on the valley floors as bajadas.

False

Ventifacts are rocks with rounded water-abraded surfaces.

False

Because of their low rainfall, intermittent stream flow, and dry stream beds, desert lack ____.

through-flowing streams

Wind-blown sand may sculpt isolated pebbles, cobbles, or boulders into ____.

ventrifacts

This agent of erosion and deposition is most effective on fine sediment that is dry.

wind

_____ is the dominant agent of erosion in desert regions.

Running water

Dune types are influenced by wind velocity.

True

Loess is a deposit of wind-blown silt primarily composed of unweathered angular grains of quartz and feldspar.

True

Most sand dunes are asymmetric in cross section with a gentle slope facing the wind and a steeper slope on the downwind side.

True

Some of the world's deserts are the result of the rain shadow effect of mountain ranges.

True

The Basin and Range province is characterized by rugged mountain ranges bounded by faults.

True

The world's best-known deserts lie in a belt 10-15 degrees centered at latitude of 30 degree (North and South).

True

Thin rocky soil and slow rates of creep make desert topography steep and angular.

True

Where sand supply is limited a barchan dune generally develops.

True