Geoscience Reference
In-Depth Information
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wet
dry
Figure 16.5
The morphology of valleys within the Colorado
Plateau developed by groundwater seepage erosion: (a) the
amphitheatre valley head of Bowns Canyon with well-developed
alcoves, (b) the amphitheatre valley head of Explorer Canyon
showing the zone of seepage emergence (photographs courtesy
of Julie Laity).
(c)
Figure 16.6
Variability in the morphology of valley heads
produced by groundwater seepage erosion: (a) amphitheatre-
headed valley produced by seepage erosion in rocks with a high
angle of internal friction, (b) valley head formed by seepage
erosion in rocks that either have a lower angle of internal
friction or are more susceptible to mass-wasting, (c) valley
heads where seepage erosion makes only a minor contribution
to valley morphology (after Dunne, 1990).
feature of groundwater outflow networks may not be
present (Figure 16.6) if erosion by surface flow and hill-
slope processes exceeds erosion by groundwater seepage
(Sakura, Mochizuki and Kawasaki, 1987). This will partly
depend upon local climatic characteristics but will also
be greatly affected by the angle of internal resistance of
the material within which the valley has developed. Val-
leys such as those with near-vertical canyon walls in the
Colorado Plateau (developed predominantly by seepage
