Ch. 19 Deserts and Wind Geo
Most dry lands exist between ________ degrees latitude on either side of the equator.
20 and 30
About what percentage of Earth's land area is covered by dry regions such as deserts and steppes?
30 %
What is the definition of an ephemeral stream?
An intermittent stream that only has water after specific episodes of rain
Which desert location in the United States consists of alternating mountain ranges and flat-bottomed valleys as a result of fault block mountains?
Basin and Range Province
Which of the following is characteristic of a desert stream?
Desert streams lack expansive tributary systems.
How does the rate of rock weathering in dry climates compare with the rate in humid regions?
Dry climates have much lower rates of chemical weathering and mechanical weathering than humid climates.
Why is it impossible to define the boundary between humid climates and dry climates by a single precipitation amount?
Dryness is not only related to annual precipitation totals, but is also a function of evaporation.
A true desert is defined by how hot it is.
False
Complete the sentences below about desert erosion processes. Match the words in the left column to the appropriate blanks in the sentences on the right.
Fine-grained surface sediments are eroded by wind during deflation. Wind can cause sand grains that are too heavy to remain suspended in the air to bounce or roll along the ground - a process called saltation. All forms of erosion remove materials from the landscape surface. Deposition of sediment occurs when the wind carrying the sediments stops or slows such that it can no longer hold them. Rocks are abraded when they are scratched by sediment particles moved by wind.
The cross bedding in a preserved layer of sandstone dips (tilts downward) to the East. What can be inferred about the wind direction at the time of deposition?
From West to East
There are many names for ephemeral desert streams that remain empty for most of the year. Which of the following is not another name for an ephemeral desert stream?
Playa
Which of the following can contain large quantities of evaporite minerals such as borate and halite?
Playa
Cross beds are a preserved record of what?
The deposition of sand on the leeward side of a dune.
Why doesn't interior drainage, such as the drainage that develops in deserts, flow out of the desert?
The water evaporates before the stream can exit the desert region.
Why is it so difficult for wind to pick up clay-sized particles?
The wind has a near-zero velocity closest to the surface and can't pick them up.
Sandstorms should be more accurately referred to as siltstorms because most sediment carried by wind for long distances is actually silt-sized.
True
The process of expanding deserts is known as desertification.
True
How is loess related to glaciers?
When glaciers retreat, their meltwater contains loess, which can be picked up by winds and distributed elsewhere.
Why do desert dunes migrate?
Wind erodes material on the windward side of the dune and deposits it on the leeward side of the dune.
What is an ephemeral stream?
an intermittent stream that carries water only in response to specific episodes of rainfall
What size sediment can be transported by wind? CHOOSE ALL THAT APPLY.
clay silt sand
What are cross beds?
inclined layers in sediment or sedimentary rocks that reveal the direction of wave or wind transport
Deposits of silt carried by blowing winds are referred to as ________.
loess
A steep-sided, flat-topped desert hill is known as a(n) ________.
mesa
A rainshadow desert forms ______.
on the leeward side of a mountain
Of the following options, which is the most common type of chemical weathering in a desert?
oxidation
Deserts form in the subtropical regions as a result of ________.
subsiding air masses
The lower limits of a blowout are controlled by ______.
the local water table
What is dust?
the particles carried in suspension by wind
A(n) ________ is a smooth, polished rock that has been abraded by the wind.
ventifact
What is the most important erosional agent in deserts?
water
From a climatological perspective, a region is a desert if ________.
yearly precipitation is less than evaporation
Match the desert landform with the correct definition.
Inselberg - bedrock knob sticking up through sediment-filled basin. Bajada - apron of sediment along the mountain front. Fault-block mountains - caused by extensional tectonics, and the underlying reason for Basin and Range topography. Alluvial fan - cone of debris at the mouth of a canyon leaving the mountains. Late stage basin and range desert - considerably flatter areas with only the occasional rocky hill.
How do pieces of rock move under the influence of wind?
rolling, sliding, bouncing, suspension
What property of a piece of material will most directly determine how it is carried by wind?
size
