Deck 17: Dry Regions: the Geology of Deserts

Question 1

A rock that has been abraded by windborne particles on multiple faces,forming a sharp edge in between,is termed a ____________.

A) blowout
B) ventifact
C) wadi
D) yardang

Answer 1

B

Question 2

The iron oxides and manganese oxides that produce desert varnish on the exterior surfaces of rocks are derived from ions ____________.

A) in the interiors of the rocks, which are transported outward by the capillary action of water
B) in the interiors of the rocks, which are transported outward by microorganisms
C) that occur naturally in rain water and precipitate out as oxides after the rain evaporates
D) that occur naturally on the surfaces of carbonate and silicate rocks

Answer 2

A

Question 3

The Atacama of Chile is a desert primarily because it is located ____________.

A) in the subtropics
B) near the geographic south pole
C) near the center of a large continent
D) next to a cold ocean current

Answer 3

D

Question 4

The Gobi of Mongolia is a desert primarily because it is located ____________.

A) in the subtropics
B) near the geographic South Pole
C) near the center of a large continent
D) next to a cold ocean current

Question 5

The most expansive hot deserts on Earth occur ____________.

A) in the tropics, at or near the equator
B) in the subtropics, between 20° and 30° north or south of the equator
C) in the temperate zone, between 30° and 50° north or south of the equator

Question 6

To qualify as a desert,a region must be ____________.

A) hot, with a mean annual temperature greater than 25°C (77°F)
B) arid, with less than 15% of the ground surface vegetated
C) both hot and arid
D) either hot or arid

Question 7

During heavy rainstorms,rates of physical weathering and erosion are ____________.

A) greater in humid climates than in deserts, because dry desert soils can soak up all of the available moisture
B) greater in deserts than in humid climates, where vegetation tends to hold soil together
C) greater in humid climates than in deserts, because vegetation in humid climates tends to break up the soil
D) about equally as fast in deserts or in humid climates

Question 8

Native Americans produced petroglyphs by etching into ____________.

A) rocks that had been painted by earlier inhabitants
B) rocks that had been coated with desert varnish
C) dark basalts
D) obsidian

Question 9

In most deserts,the scarcity of rainfall means that most of the physical weathering and erosion is accomplished by the wind.

Question 10

The highest recorded temperature on Earth was in a ____________.

A) tropical rainforest in Brazil
B) low-latitude, high-elevation desert in Mexico
C) high-latitude, high-elevation desert in Mongolia
D) low-latitude, low-elevation desert in Libya

Question 11

The Sahara of Africa is a desert primarily because it is located ____________.

A) in the subtropics
B) within the rain shadow of a mountain range
C) near the center of a large continent
D) next to a cold ocean current

Question 12

An arroyo is a steep-sided valley produced by ____________.

A) normal faulting
B) wind erosion
C) scouring erosion by water and sediment during flash floods
D) cliff retreat

Question 13

Some of the physiographic features that cause extreme aridity may be found together within a single desert,but the deserts found in the western United States form primarily due to being located ____________.

A) in the subtropics
B) within the rain shadow of one or more mountain ranges
C) near the center of a large continent
D) next to a cold ocean current

Question 14

Most regions that are now deserts have ____________.

A) been deserts throughout the geologic past
B) experienced other climates in the geologic past

Question 15

At 30° North latitude,at the northern edge of tropical (Hadley)cell convection in the northern hemisphere,____________.

A) cool, dry air sinks, becoming drier as it heats up
B) warm, moist air rises, increasing in relative humidity as it rises
C) warm, dry air rises, becoming cooler
D) cool moist air sinks, providing abundant rainfall

Question 16

As compared to humid climates,rates of chemical weathering in deserts are ____________.

A) much faster
B) much slower
C) very similar

Question 17

Saltation of sand involves ____________.

A) spherical grains rolling along the surface of dunes
B) grains bouncing into the air, traveling for a short distance, and returning to the ground
C) grains being carried long distances (up to tens of kilometers) by strong gusts of wind
D) the mixture of quartz sand with salt, which forms from the evaporation of rainwater

Question 18

Desert climate associated with a rain shadow is found ____________.

A) on the windward (shoreward) side of coastal mountain ranges
B) on the leeward (inward) side of coastal mountain ranges
C) in the middle of flat plains
D) along continental coastlines

Question 19

Deserts in coastal regions are most likely to be found where the currents are ____________.

A) warm
B) cold
C) headed toward the east
D) headed toward the west

Question 20

Most hot deserts ____________.

A) retain their high temperatures throughout the night, because there is no vegetation to absorb heat from the sediment at the surface
B) cool off greatly at night, because of sparse vegetation and little cloud cover
C) cool off slightly at night, by no more than 10°C

Question 21

A(n)____________ is a wedge of sand and gravel deposited by the distributary channels that arise when an ephemeral stream reaches a plain at the base of a slope.

A) alluvial fan
B) ventifact
C) wadi
D) yardang

Question 22

A bajada is ____________.

A) an elongate wedge of sediment at the base of a mountain range that forms from the merger of adjacent alluvial fans
B) a body of eroding rock within a desert that is broader than a butte, but less broad than a mesa
C) a dry desert cave in Mexico filled with enormous gypsum crystals
D) a desert that forms due to onshore winds associated with cold ocean currents

Question 23

Desert varnish is a coating on aerially exposed desert rocks that is primarily composed of ____________.

A) microcrystalline quartz
B) microcrystalline calcite
C) aluminum oxides and hydroxides
D) iron and manganese-oxides

Question 24

Playas are places where you would expect to find abundant ____________ exposed at the surface.

A) coal
B) igneous rock
C) evaporites (salts)
D) limestone

Question 25

The geometry of sand dunes is strongly influenced by ____________.

A) the strength of the wind
B) the consistency of wind direction
C) the abundance of sand
D) all of the above