WHAT IS GEOMORPHOLOGY? - Fundamentals of Geomorphology - page 27

denudation without waves cutting their base the longest,
while those to the east are progressively younger
(Figure 1.13). Slope profiles along Port Hudson bluff,
on the Mississippi River in Louisiana, southern USA,
reveal a chronosequence (Brunsden and Kesel 1973). The
Mississippi River was undercutting the entire bluff seg-
ment in 1722. Since then, the channel has shifted about
3 km downstream with a concomitant cessation of under-
cutting. The changing conditions at the slope bases have
reduced the mean slope angle from 40 ◦ to 22 ◦ .

of this idea is that the older and bigger a landform, the
less accurate will be predictions and postdictions about
it based upon present conditions. It also shows that an
understanding of landforms requires a variable mix of
process geomorphology and historical geomorphology,
and that the two subjects should work together rather
than stand in polar opposition.

UNIFORMITY AND
NON-UNIFORMITY: A NOTE
ON METHODOLOGY

The question of scale

A big problem faced by geomorphologists is that, as the
size of geomorphic systems increases, the explanations of
their behaviour may change. Take the case of a fluvial
system. The form and function of a larger-scale drainage
network require a different explanation from a smaller-
scale meandering river within the network, and an even
smaller-scale point bar along the meander requires a dif-
ferent explanation again. The process could carry on
down through bedforms on the point bar, to the position
and nature of individual sediment grains within the bed-
forms (cf. Schumm 1985a; 1991, 49). A similar problem
applies to the time dimension. Geomorphic systems may
be studied in action today. Such studies are short-term,
lasting for a few years or decades. Yet geomorphic systems
have a history that goes back centuries, millennia, or
millions of years. Using the results of short-term studies
to predict how geomorphic systems will change over long
periods is difficult. Stanley A. Schumm (1985, 1991)
tried to resolve the scale problem , and in doing so estab-
lished some links between process and historical studies.
He argued that, as the size and age of a landform increase,
so present conditions can explain fewer of its properties
and geomorphologists must infer more about its past.
Figure 1.14 summarizes his idea. Evidently, such small-
scale landforms and processes as sediment movement and
river bedforms may be understood with recent historical
information. River channel morphology may have a con-
siderable historical component, as when rivers flow on
alluvial plain surfaces that events during the Pleistocene
determined. Large-scale landforms, such as structurally
controlled drainage networks and mountain ranges, are
explained mainly by historical information. A corollary

Process and historical geomorphologists alike face a
problem with their methodological base. In practising
their trade, all scientists, including geomorphologists,
follow rules. Scientific practitioners established these
rules, or guidelines. They advise scientists how to go
about the business of making scientific enquiries. In
other words, they are guidelines concerned with scientific
methodology or procedures. The foremost guideline -
the uniformity of law - is the premise from which
all scientists work. It is the presupposition that natu-
ral laws are invariant in time and space. In simple terms,
this means that, throughout Earth history, the laws of
physics, chemistry, and biology have always been the
same. Water has always flowed downhill, carbon diox-
ide has always been a greenhouse gas, and most living
things have always depended upon carbon, hydrogen,
and oxygen. Three other guidelines are relevant to geo-
morphology. Unlike the uniformity of law, which is a
universally accepted basis for scientific investigation, they
are substantial claims or suppositions about how the
Earth works and are open to interpretation. First, the
principle of simplicity or, as it is commonly called in
geomorphology, the uniformity of process states that
no extra, fanciful, or unknown causes should be invoked
if available processes will do the job. It is the supposition
of actualism , the belief that past events are the out-
come of processes seen in operation today. However, the
dogma of actualism is being challenged, and its flip-side -
non-actualism - is gaining ground. Some geologists and
geomorphologists are coming round to the view that the
circumstances under which processes acted in the past
were very different from those experienced today, and