Chapter 17: The Geology of Deserts

Question 1

desert

Answer 1

a region so arid (dry) that it supports vegetation on no more than 15% of its surface; desert conditions exist where less than 25cm of rain falls per year, on average

Question 2

types of deserts

Answer 2

• subtropical
• rain-shadow deserts
• coastal deserts
• continental interior deserts
• polar deserts

Question 3

rain shadow desert

Answer 3

as moist air flows from the sea toward a coastal mountain range, the air must rise, it cools and condenses as rain. when it reaches the inland side of the mountain, it has lost all its moisture; no rain on that side

Question 4

coastal deserts

Answer 4

formed near cold ocean currents; cold ocean water cools the overlying air by absorbing heat which reduces the capacity of the air to hold moisture

Question 5

continental-interior deserts

Answer 5

as an air mass moves across a continent, it progressively loses moisture by dropping rain, even in the absence of a coastal mountain range

Question 6

polar deserts

Answer 6

so little precipitation falls in the Earth’s polar regions that these areas are, in fact arid

Question 7

desert varnish

Answer 7

a dark rusty brown coating of iron oxide, manganese oxide, and clay; forms when wind-borne dust sticks to the surface of rock. microbes in the dust extract metal ions and convert them into oxides.

Question 8

ventifacts

Answer 8

rocks whose surface has been faceted by the wind

Question 9

yardang

Answer 9

longer than they are wide; these are wind carved elongate ridges or mounds

Question 10

deflation

Answer 10

wind picks up and removes so much sediment that the land surface becomes lower

Question 11

lag deposit

Answer 11

an accumulation of coarser sediment left behind when fine-grained sediment blows away

Question 12

dunes

Answer 12

accumulation of sand into elongate mounds

Question 13

cliff retreat

Answer 13

when rock breaks away from the cliff along a joint that is parallel to the cliff face, the cliff overall retains roughly the same shape as its position migrates; occurs in fits and starts

Question 14

mesas

Answer 14

a plateau of rock slowly evolves into a cluster of isolated flat-topped hills, smaller versions are called buttes

Question 15

chimneys

Answer 15

height greatly exceeds their top surface area

Question 16

desert pavement

Answer 16

surfaces that resemble a tile mosaic in that they consist of separate stones that fit together tightly, forming a fairly smooth surface layer above a soil composed of silt and clay

Question 17

types of sand dunes

Answer 17

• barchan: crescent shape, bottom of U on the windward side
• star: results from wind shifting direction often
• traverse: wave-like shape
• parabolic: reverse barchan
• longitudinal: long strip of a dune, dune noodle