Chapter 16: Dunes

Which one of the following is an evaporite mineral?

gypsum

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.

Which of the following accurately describes the Basin and Range region of the western United States?

a region with alternating mountains and basins that have been produced by normal faulting Submit

A(n) __________ is a cone-shaped deposit of sediment that is deposited when a stream exits the mouth of a canyon.

alluvial fan

What is a playa commonly occupied by?

an ephemeral lake

Barchanoid dunes are an intermediate form of __________.

barchan and transverse dunes

Wind erosion can cause __________, which can create shallow depressions called __________.

deflation; blowouts

In the second model, wind energy diminishes between large grains of the surficial layer, leading to what?

deposition of fine-grained sediments between large grains

What type of rocks would you expect to find in a playa lake depositional environment?

evaporites and claystone

Star dunes exhibit __________.

many ridges radiating from a central point

Desert regions occur __________, and always have a(n) __________ climate zone adjacent to them.

on every continent; steppe

How do pieces of rock move under the influence of wind?

rolling, sliding, bouncing, suspension

What is the term for the rolling and bouncing of sand grains during transport?

saltation

Other than the landforms you learned about in the video, what is another landform present in the Basin and Range Province?

sand dunes

What property of a piece of material will most directly determine how it is carried by wind?

size

Cross-bedded sandstone shows inclined beds in a downward direction. What part of the ancient dune do these features represent?

slip face

Which way would wind travel in the region between 30 and 60 degrees latitude if Earth stopped rotating?Which way would wind travel in the region between 30 and 60 degrees latitude if Earth stopped rotating?

south in the Southern Hemisphere and north in the Northern Hemisphere

Which of the following is a difference between barchan and parabolic dunes?

A barchan exhibits a concave slip face, while a parabolic dune shows a convex slip face.

Label each dune with the correct arrows for wind direction. You may use labels more than once.

Barchan- Northeast Transverse- Northeast Barchanoid- Northeast Longitudinal: 2 arrows Northeast Parabolic- Northeast Star- 3 to the middle

Which of the following is true about sand dunes?

Dunes move over time.

Why does air tend to rise in equatorial regions?

Equatorial regions receive more direct sunlight than other areas.

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

The image below is an illustration of a different cross-bedded sandstone. Each layer (A-G) has a prevailing wind direction of either right or left in the sandstone outcrop illustrated below. Indicate the sequential history of the prevailing wind direction beginning with the oldest layer and ending with the youngest layer.

G: Right, F: Right, E: Right, D: Left, C: Left, B: Right, A: Left

Deserts that lie outside of the subtropics and mid-latitude belts are most likely the result of __________.

the presence of a rainshadow

Choose the correct dune type of the left dune field in the image. Use the Google Earth view of the Gigapan image to zoom into this dune field. Note that dunes are directly adjacent to shadows. This image is illuminated from the south by the sun, so shadows are above the dune crests.

transverse

What does saltating mean?

Sand grains are lifted by the wind, leap a short distance, and then fall back to the ground.

When air __________, it is compressed and warmed.

sinks

Complete the following sentences about the defining characteristics of Earth's dry regions. Match the words in the left column to the appropriate blanks in the sentences on the right. Make certain each sentence is comlete before submitting your answer. Note that some terms will remain unused.

1. Also known as steppe, [semiarid] climates are a type of dry climate that contain more water than arid climates. 2. Thick [soil] is not found in deserts because there are fewer plants than in more [humid] climates. 3. A high rate of [evaporation] is often characteristic of a climate with high temperatures and low humidity. 4. A desert has a drier climate than a [steppe].

The Trade Winds are one type of prevailing wind pattern. How many other types of prevailing winds are there among earth's global wind patterns?

2

What is the primary difference between the two desert pavement hypotheses?

Model 1 is based on a sediment volume decrease through time (erosion), while Model 2 is based on an increase in sediment volume through time (deposition).

Cross beds are a preserved record of what?

The deposition of sand on the leeward side of a dune.

Label each dune with its name.

(top to bottom) Left side: Barchan Longitudinal Middle: Transverse parabolic Right: Barchanoid Star

Which dunes are formed under varying wind directions, but are dominantly parallel to the average direction?

longitudinal

Precipitation occurs on the __________ of the mountain range, while the __________ is dry.

windward side; leeward side

Label the accompanying diagram with the environmental conditions that occur when a rain shadow forms. Pay special attention to the color-coded labels and to the descriptions referring to the east and west sides of the mountain range. Drag the appropriate labels to their respective targets. Note that some labels will remain unused.

Coastal Range- Wet climate Top middle box- Condensation forms clouds and rain Right side- dry climate

Why does wind between the equator and 30 degrees south come out of the southeast?

Cooled air moves north toward the equator and is deflected toward the west by the Coriolis effect.

In the first model, what happens as the layer of coarse material develops at the surface?

It blocks the fine-grained sediment below from the wind, which prevents the possibility of further deflation.

Not all deserts are the same. Refer to the map below, and sort the desert features by the type of desert in which they are most common. Drag the appropriate items to their respective bins.

Subtropical desert: 1) Location is due to global atmospheric patterns. 2) Form due to persistent high atmospheric pressure. Middle latitude desert: 3) Located far from major moisture sources like oceans. 4) Characterized primarily by minimal precipitation. Uncommon desert features: 5)Precipitation never occurs. 6) Plants do not grow.

In which direction would winds move at the poles if Earth rotated in the opposite direction?

Wind from the north pole would move to the southeast, and the wind from the south pole would move to the northeast.

Deflation leads to the formation of desert pavement by __________.

carrying fine sediments away and leaving a layer of larger particles at the surface

Which of the following describes favorable conditions for transverse dune formation?

areas with steady prevailing winds and abundant sand Submit

What are cross beds?

inclined layers in sediment or sedimentary rocks that reveal the direction of wave or wind transport

An isolated, heavily eroded hill or mountain that rises abruptly from a plain is a(n) __________.

inselberg

The __________ of a dune is characterized by a decrease in energy and sand avalanches, which occur due to oversteepening.

leeward side Submit

What term is used to describe the effect on air movement produced by Earth's rotation?

the Coriolis effect

What is dust?

the particles carried in suspension by wind

Which of the following statements are true? Refer again to Google Earth and the image of dune types below when selecting the correct statements from the list below.

-Erosional landforms in deserts tend to be formed more by water more than wind. -Dunes migrate as sand on the slip face reaches and exceeds the angle of repose.

Study the map below, and determine which statements about the map are true.

-If 2012 is a guide, then the center of the country is more prone to dry conditions than most of the coastal areas. -About half the states in the continental United States experienced drier-than-normal conditions.

Complete the sentences below that describe the relationships between climate change causes and effects.

1. Increased in the rate of [evaporation] due to climate change can lead to drought. 2. Although there was low precipitation during the 1930s Dust Bowl, it was the [farming methods], rather than low precipitation, that caused the extreme drought. 3. Changes in the land, such as [deforestation] through "slash and burn" practices and wildfires following overgrazing, cause the ground to dry and lead to drought. 4. Decreased rate of [precipitation] due to climate change can lead to drought. 5. Changes in the land surface, such as more [asphalt], can increase heat absorption, which can increase the rate of evaporation.

Complete the sentences below that describe the process of dune movement. Match the words in the left column to the appropriate blanks in the sentences on the right. Note that some terms will remain unused.

1. Wind bounces and rolls sand along the ground, a process called [saltation]. 2. Sediment carried by the wind will drop to the ground when the wind's [velocity] decreases. 3. The force of the [wind] pushes particles up the [windward] slope of the dune as it moves. 4. The force of [gravity] allows particles to slide down the [leeward] slope of a dune as it moves.

At what latitudes do the large-scale, convection cells bring dry air downward toward the Earth's surface?

between 20-30° north and south

Select the statements that are true about wind erosion.

-An important erosion-related role of wind in a desert is abrasion of rock surfaces. -Sediment deposited by wind in deserts can mostly be found in the form of sand dunes and loess deposits. -Wind is most effective as an erosional agent in dry places. Submit

What types of dunes would form in these scenarios?

1. What type of sand dune is shaped like a crescent and has horns that point towards the direction the wind blows? [barchan] 2. What type of sand dune resembles a sea of sand with "waves" oriented perpendicular to the wind direction? [transverse] 3. What type of sand dune occurs as very long, parallel ridges of sand with the narrow width aligned along the prevailing wind direction and is also called seif dunes? [longitudinal] 4. What type of sand dune contains two horns that point in the direction from which the wind is blowing? [parabolic] 5. What type of sand dune could be produced in a sandy desert with winds sometimes blowing from the northeast, sometimes from the west, and sometimes from the southeast? [star]

What is the natural angle of repose for sand?

34 degrees

Sort the following impacts based on whether they are expected in wet or dry climates or are a feature of other effects related to climate change.

Impacts due to lower precipitation: -decreased crop yields -increased risk of forest fire -Impacts due to higher precipitation increase potential for landslides -increased avalanche damage Impacts due to other effects of climate change: -increased risk of heat stroke -better farming at high latitudes

What is cross bedding?

Layers deposited on a dune slip face that are inclined in the direction of wind transport.

What is the air that sinks at latitudes of 30 degrees north and south like?

This air is cool and dry.