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Dec 6, 2023
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Chapter 13 Deserts Assignment
1.
Describe the general distribution of Earth’s dry lands and explain why deserts form in the subtropics.
The general distribution of earth's dry lands is 30% of Earth's land area. Deserts form because dry
climates in the subtropics are associated with the global distribution of air pressure and winds
2.
Why do middle-latitude dry regions exist? What role do mountains play?
Middle-latitude dry regions exist because they occur mostly because of the rainshadow effect, in which
moist air moving inland from oceans is intercepted by mountains.
3.
How does the rate of rock weathering in dry climates compare to the rate in humid regions?
Dry climates have much lower rates of chemical weathering and mechanical weathering than humid
climates.
4.
What are yardangs and ventifacts? How do they form?
A yardang is a streamlined, wind-sculpted landform that is oriented parallel to the prevailing wind, while
a ventifact is a polished, pitted, sharp-edged stone that formed as a result of wind-driven abrasion.
5.
What is an ephemeral stream? What is their role in shaping a desert landscape?
Deserts have ephemeral streams, which means they carry water only in response to specific episodes of
rainfall.
Because desert vegetative cover is sparse, runoff is largely unhindered and consequently
rapid, often creating flash floods along valley floors.
6.
List and briefly distinguish among basic dune types.
-Barchan dunes are crescent-shaped with their tips pointing downwind. Barchanoid dunes are somewhat
of a blend between transverse dunes and barchan dunes.
-Longitudinal dunes are long ridges formed by the wind blowing obliquely at the dune on either side.
Transverse dunes are long ridges separated by troughs oriented at right angles to the prevailing wind.
-Parabolic dunes form where vegetation partially covers the sand, with their crescent tips pointing
upwind. Star dunes have complex forms caused by variable wind directions.
7.
Describe the features and characteristics associated with each stage in the evolution of a
mountainous desert.
The early stage includes playa lakes from intermittent rainfalls and alluvial fans at the mouths of
canyons; the middle stage includes bajadas that have formed when alluvial fans coalesced together and
playas that resulted from the evaporation of water from playa lakes; the late stage includes inselbergs,
which are towers of bedrock that are the eroded remainders of the mountains that once existed.
8.
Contrast how wind transports sand with how wind transports dust.
Wind moves sand along the surface as a saltating bedload whereas dust becomes suspended in the wind
and is carried away from the region by prevailing winds, particularly during wind storms when high dust
concentrations in the air can create near "white-out" conditions.
9.
How do sand dunes migrate?
Sand moves up the gentler side of the dune by saltation and accumulates just beyond the crest of the
dune. As more sand collects, the slope steepens, and some of the sand slides down the slip face of the
dune.
10.
What is desertification? What parts of the globe are most impacted by desertification?
Desertification is the process by which semi-arid land on the edges of existing deserts become desert
and it's the persistent degradation of dryland ecosystems by human activities and by climate change. The
most impacted continents Africa and Asia where countries such as Zambia and Zimbabwe and the sub-
Himalayan Indian and north eastern china are at high risk of desertification.
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