Page 40 - Fundamentals of Geomorphology

WHAT IS GEOMORPHOLOGY? 23

a thin layer of water, surface tensions will cause enor-
Models
mous problems, and it will be impossible to simulate
tidal range and currents. Equally, material scaled down
to represent sand in the real system would be so tiny
Hardware Conceptual Mathematical
that most of it would float. These problems of scaling
are usually surmountable, to a certain extent at least, and
Scale Analogue Probabilistic Deterministic scale models are used to mimic the behaviour of a variety
of geomorphic systems. For example, scale models have
Increasing abstraction assisted studies of the dynamics of rivers and river systems
using waterproof troughs and flumes.
Figure 1.12 Types of model in geomorphology. Analogue models are more abstract scale models.The
Source: After Huggett (1993, 4) most commonly used analogue models are maps and
remotely sensed images. On a map, the surface features of
a landscape are reduced in scale and represented by sym-
case,ahardware modelrepresentsthesystem(seeMosley bols:riversbylines,reliefbycontours,andspotheightsby
and Zimpfer 1978). There are two chief kinds of hard- points, for instance. Remotely sensed images represent,
ware model: scale models and analogue models. Scale at a reduced scale, certain properties of the landscape
(or iconic) models are miniature, or sometimes gigan- systems. Maps and remotely sensed images are, except
tic, copies of systems. They differ from the systems they where a series of them be available for different times,
represent only in size. Relief models, fashioned out of static analogue models. Dynamic analogue models may
a suitable material such as plaster of Paris, have been also be built.They are hardware models in which the sys-
used to represent topography as a three-dimensional sur- tem size is changed, and in which the materials used are
face. Scale models need not be static: models made using analogous to, but not the same as, the natural materials of
materials identical to those found in Nature, but with the system.The analogous materials simulate the dynam-
the dimensions of the system scaled down, can be used ics of the real system. In a laboratory, the clay kaolin can
to simulate dynamic behaviour. In practice, scale models be used in place of ice to model the behaviour of a val-
of this kind imitate a portion of the real world so closely ley glacier. Under carefully controlled conditions, many
that they are, in effect, ‘controlled’ natural systems. An features of valley glaciers, including crevasses and step
example is Stanley A. Schumm’s (1956) use of the bad- faults, develop in the clay. Difficulties arise in this kind
lands at Perth Amboy, New Jersey, to study the evolution of analogue model, not the least of which is the prob-
of slopes and drainage basins.The great advantage of this lem of finding a material that has mechanical properties
type of scale model, in which the geometry and dynam- comparable to the material in the natural system.
ics of the model and system are virtually identical, is that Conceptual models are initial attempts to clarify
the investigator wields a high degree of control over the loose thoughts about the structure and function of a
simplified experimental conditions. Other scale models geomorphic system. They often form the basis for the
use natural materials, but the geometry of the model is construction of mathematical models. Mathematical
dissimilar to the geometry of the system it imitates – models translate the ideas encapsulated in a conceptual
the investigator scales down the size of the system. The model into the formal, symbolic logic of mathematics.
process of reducing the size of a system creates a num- The language of mathematics offers a powerful tool of
ber of awkward problems associated with scaling. For investigation limited only by the creativity of the human
instance, a model of the Severn Estuary made at a scale mind.Ofallmodesofargument,mathematicsisthemost
of 1 : 10,000 can easily preserve geometrical and topo- rigorous. Nonetheless, the act of quantification, of trans-
graphical relationships. However, when adding water, an lating ideas and observations into symbols and numbers,
actual depth of water of, say, 7 m is represented in the is in itself nothing unless validated by explanation and
model by a layer of water less than 0.7 mm deep. In such prediction. The art and science of using mathematics