GEOL107 Chapter 13 (Sand)

A broad ramp of sediment formed at the base of mountains when alluvial fans merge is

a bajada

desert varnish

a black coating that forms on the surface of a rock when the air interacts with magnesium

Basin and Range Province

a mountainous region centered on the state of Nevada

butte

a narrow hill or resistant rock with a flat top and very steep sides (most are formed by continued erosion of mesas)

rain shadow

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

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

an alluvial fan

loess

- a deposit of wind-blown silt and clay composed of unweathered grains of quartz, feldspar and other minerals weakly cemented by calcite - deposits of this may blanket hills and valleys downwind of a source of fine sediment, such as a desert or a region of glacial outwash - typically forms soils that are very fertile, yet easily eroded

parabolic dunes

- are somewhat similar ins have to barchan dunes, except that it is deeply curved and is convex in the downwind direction - the horns point upward and are commonly anchored by vegetation - requires abundant sand and commonly forms around a blowout

A(n) _____ is a broad gently sloping surface formed by the coalescing of alluvial fans.

bajada

The "horns" in a _______ dune point in a downwind direction.

barchan

Where sand supply is limited a _____ dune usually forms.

barchan

plateau

broad, flat-topped areas elevated above the surrounding land and bounded, at least in part, by cliffs (formed from flat-lying layers of resistant rock - such as sandstone, limestone, and lava flows)

A ______ is a narrow hill of resistant rock with a flat top and very steep sides found in some deserts.

butte

Colorado Plateau

centers roughly on the spot known as the Four Corners, where the states of Utah, Colorado, Arizona, and New Mexico meet at a common point

How do deserts form in coastal tropical regions?

cold ocean currents

The removal of clay, silt, and sand particles from a land surface by wind is called _____.

deflation

A surface layer of closely packed pebbles is called

desert pavement

T/F: A mesa is capped by sedimentary rocks while a butte is capped by a lava flow.

false

T/F: A playa lake is a deep long-lasting desert lake.

false

T/F: Dune sand throughout the world is composed of the stable mineral quartz.

false

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

false

mesa

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

blowout

is a depression on the land surface caused by wind erosion

How much precipitation is there in a desert?

less than 25 centimeters of rain per year

A large dune type is the _______ (or seif) dune, which forms a ridge parallel to prevailing wind direction.

longitudinal

_______ dunes in the Sahara are as high as 200 m and as long as 120 km.

longitudinal

The defining characteristic of a desert is

low rainfall

The Colorado Plateau is marked by peculiar, step-like bends in rock layers called ____.

monoclines

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

parabolic

A(n) ____ is a gently sloping erosional surface, commonly covered with a veneer of gravel, cut into the solid rock of a mountain.

pediment

A very flat surface underlain by a dry lake bed of hard, mud-cracked clay is called a

playa

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

playa

Sand moving over a dune surface by saltation typically forms ___.

ripple marks

ventifacts

rocks with flat, wind-abraded surfaces (if the wind direction shifts or the stone is turned, more than one flat face may develop on these)

How do sand grains and silt grain move differently?

- because sand grains are heavier than silt and clay, sand moves close to the ground in the leaping pattern called saltation; because of their weight sand rarely rises more than 1 meter above a flat land surface - loose silt and clay are easily picked up by wind

transverse dunes

- if more sand is available, the wind may develop this type of dune - a relatively straight, elongate dune oriented perpendicular to the wind direction

sand dunes

- mounds of loose sand grains piled up by the wind - tend to develop certain characteristic shapes, depending on (1) the wind's velocity and direction; (2) the sand supply available; and (3) how the vegetation cover, if any, is distributed

longitudinal dunes

- one of the largest types of dunes - symmetrical ridge of sand that forms parallel to the prevailing wind direction - occur in long, parallel ridges that are exceptionally straight are regularly spaced -typically separated by barren ground or desert pavement

barchan dunes

- where the sand supply is limited, this type of dune generally develops - it is crescent-shaped with a steep slip face on the inward or concave side - the horns point in the downward direction - are usually separated from one another and more across a barren surface

An area with desert conditions in the United States is ____.

Colorado Plateau

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

saltation

the movement of sand or other sediments by short jumps and bounces that is caused by wind or water

slip face

the steep downward slope of a dune

Deflation continues to deepen a blowout until it reaches ______.

the water table

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

through-flowing streams

T/F: Dune types are influenced by wind velocity.

true

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

true

T/F: Rapid down cutting of desert stream channels produces narrow canyons with vertical walls and flat gravel-strewn floors.

true

T/F: The Basin and Range province is characterized by rugged mountain ranges bounded by faults.

true

Sand grains found in dunes are commonly _______.

well sorted and well rounded

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

wind

T/F: Thin rocky soil and slow rates of creep make desert topography steep and angular.

true

Which is characteristic of deserts?

1.) internal drainage 2.) limited rainfall 3.) flash floods 4.) slow chemical weathering