Laboratory Manual for Introductory Geology 4e

FIGURE 16.10 Characteristics and evolution of a transverse dune.
Wind
(a) Transverse dunes at Stovepipe
Wells in Death Valley. Small ripples
may form on the dune surface.
Windward
side
Slip face
Dune
Surface ripples
Slip face
Cross-bed
surface
Main bedding
surface
(b) Movement of sand grains in a
transverse dune. Sand is moved from
the upwind dune face to the slip face,
causing the dune to migrate downwind.
EXERCISE 16.4
Interpreting the History of the Nebraska Sand Hills
Name:
Course:
Section:
Date:
The Nebraska Sand Hills are the remnant of a vast mid-continent sea of sand that existed beyond the Pleistocene ice front
approximately 30,000 years ago. More humid conditions today permit grasses, trees, and shrubs to stabilize the dunes so
that they no longer move across the countryside like those in Death Valley or the Sahara, but the hills preserve evidence
of the more arid conditions under which they formed. Examine the topographic overview of the Nebraska Sand Hills
(FIG. 16.11) and answer the following questions:
(a) What evidence is there that this region is still relatively arid?
(b) Describe the general topographic grain of the area, including the size and shape of the ridges and valleys present.
(continued )
16.4 WIND AND SAND DUNES
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