Chapter 17: The Geology of Deserts Flashcards
desert
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
types of deserts
- subtropical
- rain-shadow deserts
- coastal deserts
- continental interior deserts
- polar deserts
rain shadow desert
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
coastal deserts
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
continental-interior deserts
as an air mass moves across a continent, it progressively loses moisture by dropping rain, even in the absence of a coastal mountain range
polar deserts
so little precipitation falls in the Earth’s polar regions that these areas are, in fact arid
desert varnish
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.
ventifacts
rocks whose surface has been faceted by the wind
yardang
longer than they are wide; these are wind carved elongate ridges or mounds
deflation
wind picks up and removes so much sediment that the land surface becomes lower
lag deposit
an accumulation of coarser sediment left behind when fine-grained sediment blows away
dunes
accumulation of sand into elongate mounds
cliff retreat
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
mesas
a plateau of rock slowly evolves into a cluster of isolated flat-topped hills, smaller versions are called buttes
chimneys
height greatly exceeds their top surface area
