Page 44 - Fundamentals of Geomorphology

WHAT IS GEOMORPHOLOGY? 27

denudation without waves cutting their base the longest, of this idea is that the older and bigger a landform, the
while those to the east are progressively younger less accurate will be predictions and postdictions about
(Figure 1.13). Slope profiles along Port Hudson bluff, it based upon present conditions. It also shows that an
on the Mississippi River in Louisiana, southern USA, understanding of landforms requires a variable mix of
reveal a chronosequence (Brunsden and Kesel 1973).The process geomorphology and historical geomorphology,
Mississippi River was undercutting the entire bluff seg- and that the two subjects should work together rather
ment in 1722. Since then, the channel has shifted about than stand in polar opposition.
3kmdownstreamwithaconcomitantcessationofunder-
cutting. The changing conditions at the slope bases have
reduced the mean slope angle from 40 to 22 . UNIFORMITY AND
◦
◦
NON-UNIFORMITY: A NOTE
ON METHODOLOGY
The question of scale
A big problem faced by geomorphologists is that, as the Process and historical geomorphologists alike face a
size of geomorphic systems increases, the explanations of problem with their methodological base. In practising
their behaviour may change. Take the case of a fluvial their trade, all scientists, including geomorphologists,
system. The form and function of a larger-scale drainage follow rules. Scientific practitioners established these
network require a different explanation from a smaller- rules, or guidelines. They advise scientists how to go
scale meandering river within the network, and an even about the business of making scientific enquiries. In
smaller-scale point bar along the meander requires a dif- other words, they are guidelines concerned with scientific
ferent explanation again. The process could carry on methodology or procedures. The foremost guideline –
down through bedforms on the point bar, to the position the uniformity of law – is the premise from which
and nature of individual sediment grains within the bed- all scientists work. It is the presupposition that natu-
forms (cf. Schumm 1985a; 1991, 49). A similar problem ral laws are invariant in time and space. In simple terms,
applies to the time dimension. Geomorphic systems may this means that, throughout Earth history, the laws of
be studied in action today. Such studies are short-term, physics, chemistry, and biology have always been the
lasting for a few years or decades. Yet geomorphic systems same. Water has always flowed downhill, carbon diox-
have a history that goes back centuries, millennia, or ide has always been a greenhouse gas, and most living
millions of years. Using the results of short-term studies things have always depended upon carbon, hydrogen,
to predict how geomorphic systems will change over long and oxygen. Three other guidelines are relevant to geo-
periods is difficult. Stanley A. Schumm (1985, 1991) morphology. Unlike the uniformity of law, which is a
tried to resolve the scale problem, and in doing so estab- universally accepted basis for scientific investigation, they
lished some links between process and historical studies. are substantial claims or suppositions about how the
He argued that, as the size and age of a landform increase, Earth works and are open to interpretation. First, the
so present conditions can explain fewer of its properties principle of simplicity or, as it is commonly called in
and geomorphologists must infer more about its past. geomorphology, the uniformity of process states that
Figure 1.14 summarizes his idea. Evidently, such small- no extra, fanciful, or unknown causes should be invoked
scale landforms and processes as sediment movement and if available processes will do the job. It is the supposition
river bedforms may be understood with recent historical of actualism, the belief that past events are the out-
information. River channel morphology may have a con- come of processes seen in operation today. However, the
siderable historical component, as when rivers flow on dogma of actualism is being challenged, and its flip-side –
alluvial plain surfaces that events during the Pleistocene non-actualism – is gaining ground. Some geologists and
determined. Large-scale landforms, such as structurally geomorphologists are coming round to the view that the
controlled drainage networks and mountain ranges, are circumstances under which processes acted in the past
explained mainly by historical information. A corollary were very different from those experienced today, and