Geoscience Reference
In-Depth Information
A
Well developed pavement.
B
Plant mound with small animal burrows.
C
F
Plant scar.
Vegetated channel fed by pavement runoff.
Figure 9.12
Photographs of features corresponding to (A), (B), (C) and (F) in Figure 9.11.
The degree of animal activity and burrowing appears
to be higher on pavements with more vegetation and ex-
posed bare soil (Wood, Graham and Wells, 2005). In turn,
burrowing and bioturbation help to produce a mosaic of
different surface characteristics within a desert pavement.
In general, animals prefer to dig in friable soils under-
neath large plants and therefore pavements tend to lack
burrows (Figure 9.12). On a 580 000-year-old basalt flow
in the Cima Volcanic field, six distinctive surface mo-
saic types were identified, ranging from three classified
as desert pavement (surface clast coverage
and McDonald, 2006). Bioturbation by burrowing animals
produced plant scar mounds and depressions that are read-
ily visible on aerial imagery (Figure 9.11 and 9.12(c)).
Gravity-driven processes, often aided by animal move-
ment, affect the formation of pavement on slopes. In addi-
tion, hydraulic action influences the alignment or fabric of
clasts, which may be oriented with their long axes parallel
to the downslope direction (Abrahams
et al.
, 1990).
9.8.3
Regeneration of surfaces by rainfall
and runoff events
>
65 %) to
<
three that appeared as bare ground (
65 % clast cover-
age). One of the bare ground surface mosaics (GB2) con-
sisted of a 58 % cover of subangular carbonate-encrusted
medium to coarse gravel fragments that appeared to result
from excavations by burrowing mammals (Wood, Graham
and Wells, 2005). Burrows were absent on the pavement
mosaics.
The presence of plant scars on barren pavements in arid
parts of the American southwest suggests that vegetation
Pavements whose surfaces have been disturbed can
recover by rainfall and runoff events (Figure 9.6).
Wainwright, Parsons and Abrahams (1999) conducted a
study at Walnut Gulch, Arizona, in which surface stones
were mixed with the fine substrate to investigate the effect
of raindrop erosion processes on stone pavement regener-
ation. Significant accumulations of coarse particles were
