Geology Reference
In-Depth Information
Propagating Topography at Range Scale
Steady-State Landscape:
Bedrock Uplift = Erosion
A
A
Ba
cooling rates
(proxies for erosion)
river incision &
hillslope erosion
42.5°
map
view
G Y
rapid
West
East
rapid
74°
74.5°
75°
75.5°
intermediate
B
Steady
Morphology
Zone
intermediate
Transition
Zone
Surface
U
plift Zon
e
Decay?
5
50
slow
40
slow
n
30
B
Steady-State:
Threshold Slopes
20
propaga
tio
n
10
initiation
of uplift
1
Ma
>
Ma
Ma
eroded
material
0
0
0
50
100
150
Distance East (km)
rapid
Fig. 10.27
Topographic steady state in the
thrust-bounded Kyrgyz Range.
A. Map view of catchment boundaries and major faults
on the northern and eastern flank of the Kyrgyz Range
in northern Kyrgyzstan. Note the decrease in catchment
size in the propagation direction (toward the east).
B. Along-strike changes in slope, mean elevation, and
maximum elevation in the western Kyrgyz Range. The
timing of the initiation of uplift is derived from apatite
fission-track ages in relief transects (Bullen
et al
., 2003;
Sobel
et al
., 2006). The eastern tip of the range displays
increases in slope, mean elevation, and peak heights,
whereas these characteristics remain steady in the
central range, where a topographic steady state is
deduced. Modified after Sobel
et al
. (2006).
intermediate
bedrock
angle of
repose
slow
Steady-State:
Slopes Below Threshold
C
rapid
intermediate
topographic signatures can be envisioned to
define the relationship between slopes, rock uplift,
and denudation rates (Fig. 10.28). In the first
scenario, slopes vary in some proportion to the
rock uplift rate, under the assumption that the flux
of material from hillslopes can be summarized as
a diffusive process that is strongly related to slope
angle (Penck, 1953). Alternatively, if most of the
hillslope sediment flux is delivered by landslides,
then most slopes would lie close to the threshold
angle for failure (Fig. 10.28) and, hence, would
have similar slopes even among areas with
differing rock uplift rates. In both cases, the rate of
river incision could balance the rock uplift rate.
Some studies seem to bridge between these
slow
Fig. 10.28
Different ways to attain a topographic
steady state.
A. If variations in cooling rates or rock uplift
correlate spatially with variations in denudation or
incision, a steady-state topography is commonly
inferred. B. If slopes everywhere are at threshold
angles for stability, then hillslope angles will be
independent of the erosion rate (assuming uniform
rock strength), and denudation will be solely a
function of the rate of local base-level lowering.
C. If slopes are proportional to the denudation
rate, then spatial variations in slope would correlate
with variations in rock uplift.
