Page 22 - Fundamentals of Geomorphology

WHAT IS GEOMORPHOLOGY? 5

Box 1.1

THE ORIGIN OF GEOMORPHOLOGY

Ancient Greek and Roman philosophers wondered hollowing out softer rocks. During the Renaissance,
how mountains and other surface features in the many scholars debated Earth history. Leonardo da
natural landscape had formed. Aristotle, Herodotus, Vinci (1452–1519) believed that changes in the levels
Seneca, Strabo, Xenophanes, and many others dis- of land and sea explained the presence of fossil marine
coursed on topics such as the origin of river valleys shells in mountains. He also opined that valleys were
and deltas, and the presence of seashells in mountains. cut by streams and that streams carried material from
Xenophanes of Colophon (c. 580–480 BC) speculated one place and deposited it elsewhere. In the eighteenth
that, as seashells are found on the tops of moun- century, Giovanni Targioni-Tozzetti (1712–84) recog-
tains, the surface of the Earth must have risen and nized evidence of stream erosion. He argued that the
fallen. Herodotus (c. 484–420 BC) thought that the valleys of the Arno, Val di Chaina, and Ombrosa in
lower part of Egypt was a former marine bay, reput- Italy were excavated by rivers and floods resulting from
edly saying ‘Egypt is the gift of the river’, referring the bursting of barrier lakes, and suggested that the
to the year-by-year accumulation of river-borne silt in irregular courses of streams relate to the differences
the Nile delta region. Aristotle (384–322 BC) conjec- in the rocks in which they cut, a process now called
tured that land and sea change places, with areas that differential erosion. Jean-Étienne Guettard (1715–86)
are now dry land once being sea and areas that are argued that streams destroy mountains and the sedi-
now sea once being dry land. Strabo (64/63 BC–AD ment produced in the process builds floodplains before
23?) observed that the land rises and falls, and sug- being carried to the sea. He also pointed to the effi-
gested that the size of a river delta depends on the cacy of marine erosion, noting the rapid destruction
nature of its catchment, the largest deltas being found of chalk cliffs in northern France by the sea, and the
where the catchment areas are large and the surface fact that the mountains of the Auvergne were extinct
rocks within it are weak. Lucius Annaeus Seneca (4 BC– volcanoes. Horace-Bénédict de Saussure (1740–99)
AD 65) appears to have appreciated that rivers possess contended that valleys were produced by the streams
the power to erode their valleys. About a millennium that flow within them, and that glaciers may erode
later, the illustrious Arab scholar ibn-Sina, also known rocks. From these early ideas on the origin of landforms
as Avicenna (980–1037), who translated Aristotle, arose modern geomorphology. (See Chorley et al. 1964
propounded the view that some mountains are pro- and Kennedy 2005 for details on the development of
duced by differential erosion, running water and wind the subject.)

and are affected by, human activities. Applied geomor- parts of the world, some landforms survive from millions
phologists explore this rich area of enquiry, which is and hundreds of millions of years ago. Geomorphology,
largely an extension of process geomorphology. Many then, has an important historical dimension, which is the
landforms have a long history, and their present form domain of the historical geomorphologists. In short,
does not always relate to the current processes acting modern geomorphologists study three chief aspects of
upon them.The nature and rate of geomorphic processes landforms – form, process, and history. The first two
change with time, and some landforms were produced are sometimes termed functional geomorphology, the
under different environmental conditions, surviving last historical geomorphology (Chorley 1978). Process
today as relict features. In high latitudes, many land- studies have enjoyed hegemony for some three or four
forms are relicts from the Quaternary glaciations; but, in decades. Historical studies were sidelined by process