Geomorphology: Earth Landforms

Geomorphology is the study of
landforms and landscapes, including
the description, classifiation, origin,
development, and history of planetar
surfaces. During the early part of
this century, the study of regional-
scale geomorphology was termed
"physiography"(Salisbury, 1907).
Unfortunately, physiography also
became synonymouswith physical
geography, and the concept became
embroiled in controversy
surrounding the appropriate
concerns of that discipline. Some
geomorphologists held to a
geological basis for physiography
and emphasized a concept of
physiographic regions (Fenneman,
1938), A conflicting trend among
geographers was to equate
physiography with "pure
morphology," divorced of its
geological heritage. In the period
following World War II, the
emergence of process, climatic, and
quantitative studies led to a
preference by many Earth scientists
for the term "geomorphology" in
order to suggest an analytical
approach to landscapes rather than
a descriptive one.

In the second half of the twentieth
century, the study of regional-scale
geomorphology -the original
physiography- was generally
neglected. Russell (1958) attributed
the decline of physiography to its
elaborate terminology and to its
detachment from evidence acquired
by other disciplines, chiefly geology.
Although the concept of
physiographic regions endured
among geologists (Thornbury, 1965;
Hunt, 1967), geographers became
much more interested in the details
of man/land interactions and in the
applications of modeling and
systems analysis (Chorley and
Kennedy, 1971) to geomorphology.
In the exploration of planetary
surfaces by various space missions,
the perspective of regional
geomorphology has been the
required starting point for scientific
inquiry. Global studies of Mars
(Mutch et al., 1976), the Moon
(McCauley and Wilhelms, 1971),
Mercury (Strom, 1984), and Venus
(Masursky et al., 1980) resulted in
the identification of "surface
units"or physiographic provinces.
The Colorado Plateau (Plate I-1) is
an excellent example of a terrestrial
physiographic province. Plate I-1
illustrates the use of a large-scale
perspective to focus on this naturally
defined region.

The term "mega-geomorphology" was
introduced in March 1981 at the 21st
anniversary meeting of the British
Geomorpholgy Research Group. The
proceedings of that meeting
(Gardner and Scoging, 1983) reveal
that the concept was not well
defined. It clearly involves a return
by geomorphologists to the study of
phenomena on large spatial scales,
ranging from regions to continents to
planets. It also involves large time
scales. Nevertheless, mega-
geomorphology is merely a
convenient term, unencumbered by
past philosophical trappings, that
emphasizes planetary surface studies
at large scales.
The interrelation of temporal and
spatial scales in geomorphology is
illustrated by the tentative
classification shown in Table 1-1 . Of
course, such a hierarchial ordering
of geomorphic features is far from
satisfying. As stated by Sparks
(1971), classifications are arbitrary
constructions designed to facilitate
the discussionof diverse phenomena
at the risk of some distortion of the
truth. The scheme merely illustrates
what was well known to the great
geomorphologists at the last turn of
the century. The large first order
features, continents and ocean
basins, persist and evolve over long
time scales. Small high-order
features are transient. Fundamental
units appear at different orders. The
old concept of physiographic regions
was used to designate second- order
forms, such as entire mountain
ranges or coastal plains. Massive
entities within a physiographic
region might constitute a third-order
form, such as a domal uplift. The
details of the classification are
unimportant as the analysis moves
on to exploring the explanation of
phenomena.