Geoscience Reference
In-Depth Information
SEEPAGE
SLOPE
1
CONVEX
CREEP/SPLASH
SLOPE
2
3
0°
2°-4°
Modal slope angles
4
FALL FACE
(minimum angle 45°
normally over 65°)
INDICATES MOVEMENT IN
A DOWNVALLEY DIRECTION
ARROWS INDICATE DIRECTION &
RELATIVE INTENSITY OF MOVEMENT OF
WEATHERED ROCK 7 SOIL MATERIALS
BY DOMINANT GEOMORPHIC PROCESSES
TRANSPORTATIONAL MIDSLOPE
(frequently occuring
angles 26° - 35°)
5
COLLUVIAL
FOOTSLOPE
ALLUVIAL
TOESLOPE
6
CHANNEL
WALL
7
8
CHANNEL
BED
9
0°-4°
1
2
3
4
5
6
7
8
9
PREDOMINANT CONTEMPORARY GEOMORPHIC PROCESSES
Figure 10.1
The nine-unit hillslope form model of Dalrymple, Blong and Conacher (1968) as modified by Parsons (1988) showing
the different slope units, angles and dominant process mechanisms.
provides a further fundamental control in terms of vertical
crust movements (Chapters 1 and 2). In the simplest sense,
greater vertical movements generate steeper slopes and
thus faster erosion rates, but they also cause landscapes
to cross thresholds, so that other processes such as mass
movements can become important. More recent studies by
Willett (1999) have demonstrated that because of the feed-
backs between erosion and compensatory isostatic uplift,
the relative position of an arid zone to a mountain belt
is important in controlling large scale erosion rates and
landscape form. Thus, the location of drylands relative to
orogenic zones and the position of the latter in relation
to ocean currents and atmospheric circulation can lead to
significant changes in the patterns and rates of landscape
trol variability in evolution from the hillslope scale, e.g.
as a result of the distribution of joints on rock faces, to re-
gional scale as a result of faults and patterns of unloading
affecting the material strength of bedrock.
At smaller scales, a geological framework is important
because of the controls exerted by lithology on weather-
ing and erosion processes. Of course, there is a further
link here to tectonics, but also suggests that the past his-
tory of a continent can cause it to evolve in significantly
different ways. Lithological variability is also significant
over scales from kilometres to micrometres, with changes
in rock type, bedding and particle arrangement all be-
ing potentially important sources of variation in material
strength and thus ability to respond to the forces imposed
