Laboratory Manual for Introductory Geology 4e

LEARNING
OBJECTIVES
■■
Understand how erosion and
deposition in arid regions
differ from those processes in
humid regions
■■
Recognize how these
differences make arid
landscapes unlike those of
humid environments
■■
Become familiar with landforms
and landscapes of arid regions
■■
Understand natural
desertification and the impact
of humans on this phenomenon
MATERIALS NEEDED
■■
Colored pencils
■■
Ruler (included in the Geo
Tools section at the back of
this manual) and graph paper
(provided at the end of this
chapter) for constructing
topographic profiles
16.1 Introduction
Arid regions are defined as those that receive less than 25 cm (10 in.) of rain per year,
which provides very little water for chemical and physical weathering or for stream
and groundwater erosion. Weathering, mass wasting, and wind and stream erosion
are the major factors in developing arid landscapes, but because these processes
are operating in very different proportions than in humid regions, their results are
strikingly different from those in temperate and tropical landscapes (FIG. 16.1).
Movies and television portray arid regions with camels resting at oases amid
mountainous sand dunes. Some arid regions, such as parts of the Sahara and Mojave
deserts, do look like that (minus camels in the Mojave). But some arid regions actually
have more rock than sand, whereas others, surprisingly, lie next to shorelines,
where there is no shortage of water—and even the North and South Poles rank
among the Earth’s most arid regions (FIG. 16.2).
With these factors in mind, compare the arid and humid landscapes in Exercise 16.1.
FIGURE 16.1 Arid landforms from the southwestern United States.
(a) Erosional remnants in Monument Valley, Arizona.
(b) Hoodoo panorama in Bryce Canyon, Utah.
(c) Delicate Arch in Arches National Park, Utah.
410 CHAPTER 16 PROCESSES AND LANDFORMS IN ARID ENVIRONMENTS