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Laboratory Manual for Introductory Geology 4e

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FIGURE 13.7 Evolution of stream valleys.

Initial steep valley walls

Channel

(a) Steep, V-shaped valley. Vertical erosion carves the channel and valley downward vertically

(large blue arrow), producing steep valley walls. Mass wasting (slump, creep, landslides, and

rockfalls) reduces slope steepness to the angle of repose (curved arrows) and widens the top of

the valley (dashed arrows).

Valley

Oxbow lake

Oxbow lake

Channel

(b) Broad, flat-bottomed valley. As the stream meanders, lateral erosion widens the valley

(arrows). Mass wasting reduces the slope of the valley walls, as in part (a). Oxbow lakes mark

the position of former meanders.

336 CHAPTER 13 LANDSCAPES FORMED BY STREAMS

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