Geology Reference
In-Depth Information
Box 1.1
THE ORIGIN OF GEOMORPHOLOGY
Ancient Greek and Roman philosophers wondered
how mountains and other surface features in the
natural landscape had formed. Aristotle, Herodotus,
Seneca, Strabo, Xenophanes, and many others dis-
coursed on topics such as the origin of river valleys
and deltas, and the presence of seashells in mountains.
Xenophanes of Colophon (
c.
580-480
BC
) speculated
that, as seashells are found on the tops of moun-
tains, the surface of the Earth must have risen and
fallen. Herodotus (
c.
484-420
BC
) thought that the
lower part of Egypt was a former marine bay, reput-
edly saying 'Egypt is the gift of the river', referring
to the year-by-year accumulation of river-borne silt in
the Nile delta region. Aristotle (384-322
BC
) conjec-
tured that land and sea change places, with areas that
are now dry land once being sea and areas that are
now sea once being dry land. Strabo (64/63
BC
-
AD
23?) observed that the land rises and falls, and sug-
gested that the size of a river delta depends on the
nature of its catchment, the largest deltas being found
where the catchment areas are large and the surface
rocks within it are weak. Lucius Annaeus Seneca (4
BC
-
AD
65) appears to have appreciated that rivers possess
the power to erode their valleys. About a millennium
later, the illustrious Arab scholar ibn-Sina, also known
as Avicenna (980-1037), who translated Aristotle,
propounded the view that some mountains are pro-
duced by differential erosion, running water and wind
hollowing out softer rocks. During the Renaissance,
many scholars debated Earth history. Leonardo da
Vinci (1452-1519) believed that changes in the levels
of land and sea explained the presence of fossil marine
shells in mountains. He also opined that valleys were
cut by streams and that streams carried material from
one place and deposited it elsewhere. In the eighteenth
century, Giovanni Targioni-Tozzetti (1712-84) recog-
nized evidence of stream erosion. He argued that the
valleys of the Arno, Val di Chaina, and Ombrosa in
Italy were excavated by rivers and floods resulting from
the bursting of barrier lakes, and suggested that the
irregular courses of streams relate to the differences
in the rocks in which they cut, a process now called
differential erosion. Jean-Étienne Guettard (1715-86)
argued that streams destroy mountains and the sedi-
ment produced in the process builds floodplains before
being carried to the sea. He also pointed to the effi-
cacy of marine erosion, noting the rapid destruction
of chalk cliffs in northern France by the sea, and the
fact that the mountains of the Auvergne were extinct
volcanoes. Horace-Bénédict de Saussure (1740-99)
contended that valleys were produced by the streams
that flow within them, and that glaciers may erode
rocks. From these early ideas on the origin of landforms
arose modern geomorphology. (See Chorley
et al
. 1964
and Kennedy 2005 for details on the development of
the subject.)
and are affected by, human activities. Applied geomor-
phologists explore this rich area of enquiry, which is
largely an extension of process geomorphology. Many
landforms have a long history, and their present form
does not always relate to the current processes acting
upon them. The nature and rate of geomorphic processes
change with time, and some landforms were produced
under different environmental conditions, surviving
today as relict features. In high latitudes, many land-
forms are relicts from the Quaternary glaciations; but, in
parts of the world, some landforms survive from millions
and hundreds of millions of years ago. Geomorphology,
then, has an important historical dimension, which is the
domain of the
historical geomorphologists
. In short,
modern geomorphologists study three chief aspects of
landforms -
form
,
process
, and
history
. The first two
are sometimes termed functional geomorphology, the
last historical geomorphology (Chorley 1978). Process
studies have enjoyed hegemony for some three or four
decades. Historical studies were sidelined by process
