Question 1

Most dunes are symmetrical.

Accepted Answer

Most dunes are actually asymmetrical, with a gentler slope on the windward side and a steeper slope on the leeward side. This is due to the constant reshaping of the dune by the wind, which constantly adds sand to the windward side and removes it from the leeward side. However, some dunes may appear symmetrical if they are not very large or if the wind patterns that created them were relatively steady.

Question 2

Desert streams usually receive their moisture from wetter, mountainous lands on their borders.

Accepted Answer

Desert streams are often fed by rainfall or snowmelt from mountains and highlands surrounding the desert area. These upstream sources provide vital water resources for the otherwise dry and arid desert ecosystems.

Question 3

Windblown sand is an effective agent of erosion.

Accepted Answer

Windblown sand is a type of aeolian erosion, which is defined as erosion caused by wind.

Question 4

Deserts never occur along coastlines.

Accepted Answer

Deserts can occur along coastlines, specifically in regions where there is a strong coastal upwelling that leads to cold water temperatures and dry air. One example is the Atacama Desert in South America, which is situated along the Pacific coastline.

Question 5

Migrating dunes can overrun buildings and highways.

Accepted Answer

Migrating dunes, also known as sand dunes, can move at a rate of several meters per year and can overrun buildings and highways if not properly managed.

Question 6

Loess is:
A) silt that has been transported and deposited by wind.
B) a type of glacial moraine.
C) a dried-out river bed.
D) a fossil dune.

Accepted Answer

Loess is a type of sediment consisting of mostly silt that has been transported and deposited by wind. It is typically found in areas where the wind can easily pick up and move sediment, such as near deserts or on the edges of glaciers. Loess is known for its ability to retain water, making it a valuable soil for agriculture in some areas.

Question 7

The Atacama Desert along the west coast of South America is so dry that, on the average, portions of Peru and Chile receive no rainfall for a decade or more.

Accepted Answer

The statement is true. The Atacama Desert is one of the driest places on Earth and some areas have gone without rainfall for over 400 years.

Question 8

Desertification in the Sahel in the late 1960s and early 1970s probably happened because of:
A) movement of the African continent.
B) tectonic uplift.
C) volcanic activity.
D) human mismanagement.

Accepted Answer

Studies suggest that desertification in the Sahel was caused by human mismanagement, such as overgrazing, deforestation, and unsustainable agricultural practices, rather than natural causes like tectonic uplift or volcanic activity.

Question 9

A bajada is an erosional surface.

Accepted Answer

A bajada is not an erosional surface, but rather a sloping plain formed by the coalescence of alluvial fans.

Question 10

The sand on the slip face of a dune is loose compared to the windward face.

Accepted Answer

The windward face of a dune is the side facing the wind and is often steep and compacted due to the constant pounding of wind, while the slip face is the side facing away from the wind and is often looser due to the wind carrying sand particles away. Therefore, the sand on the slip face of a dune is indeed loose compared to the windward face.

Question 11

Because sand grains are relatively heavy, wind rarely lifts sand more than 1 meter above the ground and carries it only short distances.

Accepted Answer

Sand grains are indeed relatively heavy, which limits their suspension by wind to usually no more than about 1 meter above the ground. Wind-blown sand typically moves by saltation, bouncing along the ground, rather than being carried aloft over long distances.

Question 12

The day after a flash flood, a desert wash may contain only a tiny trickle, and within 24 hours, it may be completely dry again.

Accepted Answer

Flash floods are common in deserts due to the lack of vegetation to absorb water. However, the water quickly dissipates or evaporates, leaving the wash dry once again.

Question 13

Rainfall patterns and deserts have no direct relationship to tectonic activity.

Accepted Answer

Tectonic activity can affect rainfall patterns by creating or altering topography, which can in turn impact the amount and distribution of precipitation. Additionally, tectonic activity can lead to the creation of mountains and other landforms that can provide the necessary conditions for desert formation.

Question 14

Many of the world's largest deserts lie at about 30° north and south of the equator.

Accepted Answer

This statement is true. Examples of deserts that lie at about 30° north and south of the equator include the Sahara, Arabian, Mojave, Sonoran, and Atacama deserts.

Question 15

In fossil dunes:
A) numerous fossils form limestone.
B) numerous fossils have been obliterated by wind action.
C) the dipping beds are the layering of the dune's windward face.
D) the dipping beds are the layering of the dune's slip face.

Accepted Answer

The dipping beds in fossil dunes represent the layering of the dune's slip face, which is the steep, leeward side of the dune where sand accumulates and slides down, creating distinct layers over time.

Question 16

When a barchan dune migrates, the edges move more slowly because there is more sand to transport.

Accepted Answer

The edges of a barchan dune move more quickly than the center because there is less sand at the edges, making them lighter and more easily moved by the wind.

Question 17

When moisture-laden air flows over a mountain range, it cools and loses its ability to hold moisture.

Accepted Answer

This is because as the air rises over the mountain range, it expands and cools. As it cools, the relative humidity increases and if the temperature drops below the dew point, the moisture in the air condenses and forms clouds. This is why mountains often have higher precipitation than surrounding areas.

Question 18

The effects of abrasion by windblown sand and silt:
A) form blowouts.
B) are responsible for the delicate caps on high desert pinnacles.
C) are concentrated close to the ground.
D) form playa lakes.

Accepted Answer

Abrasion by windblown sand and silt is most effective close to the ground because the particles carried by the wind tend to be concentrated at lower elevations due to gravity and the nature of wind flow near the surface.

Question 19

Much of the rich loess of the central plains of the United States is the result of the Pleistocene Ice Age.

Accepted Answer

During the Pleistocene Ice Age, glaciers formed and melted several times, depositing huge amounts of sediment and creating the rich loess soil of the central plains of the United States.

Question 20

Wind erodes sand:
A) from both sides of a dune.
B) from the leeward side of a dune, and deposits it on the windward side.
C) from the windward side of a dune, and deposits it on the sheltered leeward side.
D) only from the top of a dune.

Accepted Answer

Wind erodes sand from the windward side of a dune, where the wind hits the dune directly, and deposits it on the leeward side, which is sheltered from the wind. This process causes the dune to slowly move over time.

Quiz 14: Deserts and Wind