Geoscience Reference
In-Depth Information
Figure 10.13
Desert caprocks overlying more erodible sandstone substrates.
10.3.1.4 Aeolian scour pits
Such features may range in size from a few to many metres
in diameter and depth and tend to be formed by circulat-
ing vortices of wind, which entrain individual sand parti-
cles and deposit them as sand dunes further downslope or
within the scour pit base. Loope
et al
. (2008) suggest that
fluvial action cannot be responsible for the formation of
these features as sufficient catchment areas are not present
to provide enough energy for water erosion processes to
entrain sediment. These features occur in bedrock that is
highly exposed to the dominant wind direction and where
the wind blows consistently throughout the year.
10.3.1.5 Treads and risers/aeolian ripples
In similar localities to the scour pits described above, rock
slopes are dominated by small-scale ripple features that
cover many of the Navajo sandstone slick-rock slopes in
the study area (Loope, Rowe and Joeckel, 2001). These
features are in part controlled by the binding action of mi-
crobial layers in the surface rock, rather than the strata or
bedding of the rock, in interaction with the consistent abra-
sion by the wind. Figure 10.15 shows the characteristic
form of these aeolian erosional features and the extent to
which they cover entire faces of exposed bedrock slopes.
It is argued by Loope
et al
. (2008) that such ripples are
Caprock
Caprock
face
Substrate
face
Substrate
Substrate
ramp
Talus
flatiron
B
A
C
D
Talus embankment
Figure 10.14
Model of compound scarp development: A, generalized form of compound scarp composed of caprock face and
substrate ramp; B, erosion of caprock brow and substrate ramp, with downward cliff expansion into substrate; C, failure of
substrate face and collapse of unsupported caprock, producing talus embankment on substrate ramp; D, erosion of caprock brow,
talus embankment and substrate ramp; erosion of talus embankment produces talus flatirons; downward cliff extension into
