Geology Reference
In-Depth Information
()
a
Form system
()
b
Flow or cascading
system
()
c
Process-form or
process-response
system
123
Cliff
Rockfall
Cliff
Covered
cliff face
at time 2
Talus
Talus
Lower
slope
Lower
slope
Time
3
2
1
Figure 1.8
A cliff and talus slope viewed as (a) a form system, (b) a flow or cascading system, and (c) a process-form or
process-response system. Details are given in the text.
shown in Figure 1.8a, which depicts a cliff with a
talus slope at its base. All that could be learnt from
this 'form system' is that the talus lies below the cliff;
no causal connections between the processes linking
the cliff and talus slope are inferred. Sophisticated
characterizations of hillslope and land-surface forms
may be made using digital terrain models.
the system processes. A hillslope may be viewed in
this way with slope form variables and slope process
variables interacting. In the cliff-and-talus example,
rock falling off the cliff builds up the talus store
(Figure 1.8c). However, as the talus store increases
in size, so it begins to bury the cliff face, reduc-
ing the area that supplies debris. In consequence,
the rate of talus growth diminishes and the sys-
tem changes at an ever-decreasing rate. The process
described is an example of negative feedback, which
is an important facet of many process-form systems
(Box 1.2).
2
Process systems.
Process systems
, which are also
called
cascading
or
flow systems
, are defined as
'interconnected pathways of transport of energy or
matter or both, together with such storages of energy
and matter as may be required' (Strahler 1980, 10).
An example is a hillslope represented as a store of
materials: weathering of bedrock and wind deposi-
tion add materials to the store, and erosion by wind
and fluvial erosion at the slope base removes mate-
rials from the store. The materials pass through the
system and in doing so link the morphological com-
ponents. In the case of the cliff and talus slope, it
could be assumed that rocks and debris fall from the
cliff and deliver energy and rock debris to the talus
below (Figure 1.8b).
Geomorphic systems as simple or complex
structures
Three main types of system are recognized under this
heading: simple systems, complex but disorganized
systems, and complex and organized systems.
1
Simple systems
. The first two of these types have
a long and illustrious history of study. Since at
least the seventeenth-century revolution in science,
astronomers have referred to a set of heavenly bod-
ies connected together and acting upon each other
according to certain laws as a system. The Solar
System is the Sun and its planets. The Uranian
3
Form and process systems.
Process-form systems
,
also styled
process-response systems
, are defined
as an energy-flow system linked to a form system in
such a way that system processes may alter the system
form and, in turn, the changed system form alters
