What is Geomorphology?
The word geomorphology derives from three Greek words: gew (the Earth), morfh (form), and logo~ (discourse). Geomorphology is therefore ‘a discourse on Earth forms’. The term was coined sometime in the 1870s and 1880s to describe the morphology of the Earth’s surface , was originally defined as ‘the genetic study of topographic forms’ and was used in popular parlance by 1896.
Today, geomorphology is the study of Earth’s physical land-surface features, its land forms – rivers, hills, plains, beaches, sand dunes, and myriad others. Some also include the submarine landfors and other terrestrial type planets and satellites in the solar system.
Geomorphology investigates landforms and the processes that fashion them. Form, process, and the interrelationships between them are central to understanding the origin and develop – ment of landforms.
In geomorphology, form or morphology has three facets –
- constitution (chemical and physical properties described by material property variables),
- configuration (size and form described by geometry variables),
- and mass flow (rates of flow described by such massflow variables as discharge, precipitation rate, and evaporation rate)
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 discoursed 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 mountains, the surface of the Earth must have risen and fallen. Herodotus (c. 484–420) thought that the lower part of Egypt was a former marine bay, reputedly 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) conjectured 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 suggested 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 produced 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) recognized evidence of stream erosion. He argued that rivers and floods resulting from the bursting of barrier lakes excavated the valleys of the Arno, Val di Chaina, and Ombrosa in Italy, 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 sediment produced in the process builds floodplains before being carried to the sea. He also pointed to the efficacy 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.