Geomorphology is the branch of geography that study about the physical features of the earth surface .According to Sparks, W. B. geomorphology is the “Essentially it is the study of the evolution of landforms, especially landforms produced by erosion.” And Strahler, A. N. mentioned that it is ,“The systematic study of landforms and their origin is known as geomorphology.”
According to Small - “In its strictest sense geomorphology, the science of landform study is concerned with the study of the form of the earth.” He rules out mountains and continents as a subject of geomorphic studies. He says that “the form and origin of mountain systems… are studied more by geologists than geomorphologists.” He goes on to say that “Problems concerning the shape and distribution of the continental land-masses are at present being investigated by physicist…”
Here there is a difference between the opinions regarding the subject matter of geomorphology. According to Strahler all landforms fall under the field of geomorphology, while Sparks suggests inclusion only of those landforms that are formed by agents of erosion on the surface of the earth. Not only this, but whether geomorphology should study features formed on the continents, or should include those in the sub-marine region is also debated.The widest field of coverage appears in the following statement:
“..Not only are the landforms of the continents and their margins of concern, but also the morphology of the sea floor. In addition, the close look at the moon, Mars and other planets provided by spacecraft has created an extraterrestrial aspect to geomorphology”. This makes it clear that definitions of geomorphology embody a great variety of the subject matter within the discipline.
Secondly, the approaches to studying and the perspectives to look at these landforms also vary from scholar to scholar, but there is more or less a consensus among all of them to:
- interpret the origin and evolution, and analyse
landscapes and landforms.
Here we may have a look at some such opinions: “The geomorphologist may concern himself with question of structure, process and stage.”
“Geomorphology is the scientific study of landscapes and the processes that shape them.” – Arthur L. Bloom.
We must, however realize that no definition is final and perfect. According to Kaplan, cited by Harvey “Every term directs a beam of light onto the screen of experience, but whatever we wish to illuminate, something else must be left in its shadow.”
The definitions of geomorphology given in dictionaries/ encyclopedias are wider and all- encompassing; they incorporate most of the scattered views of the scholars. For instance, Geomorphology is “The science that treats the general configuration of the earth’s surface; especially the study of classification, description, nature, origin, and development of landforms and their relationship to underlying structures and the history of geological changes as recorded by surface features”, says the Dictionary of Geology.
Methods of Investigation in Geomorphic Studies
After understanding that geomorphology deals with landforms and landscapes, it remains to be seen how to study them in a scientific and reliable manner. There are several methods adopted by geomorphologists. The most widely used methods are:
- Deduction, and
- Lab experiments.
In general terms observation is understood as - “An act of recording and noting a fact or an occurrence.” However, technically observation follows a standardized procedure
As can be seen in figure 1.1, observation starts with collection of a large amount of data. The second step aims at retaining some and discarding the rest of the information collected, that is to say, only the information relevant for a set objective of study is focused on. The selected facts are then arranged in a logical order so that the statements made are comprehensible as a
It can be said that observation is the oldest method of studying landforms. It was used even before the science of geomorphology was born. For instance Herodotus observed the silting by Nile and concluded that the fertile fields of Egypt were formed by this process. Aristotle similarly observed shallowing of the Black Sea was a result of silting by the rivers falling into it.
Observation method has three models:
- Definition model of observation– The facts and information collected by an observer are codified as a shorthand term for a larger term or feature, such as
A delta “is a landform that is formed at the mouth of a river where that river flows into an ocean, sea, estuary, lake, reservoir, flat arid area or another river”. Here we may safely presume that the student started with the objective of defining ‘delta’. He/she first collected a lot of information from different sections of several river courses; the samples chosen covered a range of streams falling into oceans, seas, estuaries, lakes, reservoirs, another river or a flat surface in an arid region. As the concerned feature is absent everywhere other than the mouth of the rivers the definition was formulated after careful selection and rejection of the rest of the collected information.
- ”Measurement model of observation– In this the observed information is calibrated either by numerals or a descriptive scale of ‘more’ ‘less’ and ‘intermediate’ et cetera. Measurement is “an easy way to structure observation.
This may be seen in the following example:
“Densities between 1.3 and 1.8 g/cm³” are identified as debris flow, while “densities only slightly greater than 1.0 g/cm³” are identified as muddy rivers.
Here the thick slurry of water and rock debris in the above two cases may look similar to an observer and need to be distinguished. The numerical values assigned to measure the nature of the two moving masses are based on a wide range of observations. The values can now be used universally to identify similar cases. Quantified measurement of landscape forms has given birth to the sub-branch of geomorphology, called morphometry. The importance of measurement model can be seen in Lord Kelvin’s statement cited by Harvey, “when you can measure what you are speaking about, and express it in numbers, you know something about it , but you can not measure it, when you can not express it in numbers, your knowledge is of a meager and unsatisfactory kind.”
- Classification model of observation– In this model the large amount of information collected is grouped under different classes to make it easy to manipulate and comprehend.
The most well-known example of this model is Richard E. Murphy’s classification of world landforms . Without such grouping, it goes without saying, handling the innumerable landforms would be immensely problematic.
Since we are talking about classification, we can further see how classification is helpful in the study of landforms.
An exercise in classification may be defined as “A systematic arrangement into groups or categories in accordance with established criteria.”
In geomorphology different systems of classification are put to use; genetic classification is one of them. Genetic classification is absolutely different from the above example of Murphy’s landform classification, which is a generic classification. A generic classification aims at providing “a single statement of collection of common characteristics shared by objects which otherwise differ.” In the above example it is clear that all the mountains are put under one class of land forms, but they may differ as some are folded mountains while others may be volcanic in nature. The same is applicable to the other landforms in the list.
Genetic classification on the other hand is based on the birth of landforms (that is, processes responsible for its formation and characteristics resulting from such formative processes). The genetic classification, therefore, is process based. It classifies landforms according to their characteristics, which in turn are determined by the agent/agents (process/ processes) that influenced the evolution of the land feature. This classification has categories like fluvial, glacial, aeolian, periglacial and karst landforms, to name some. Besides, if the formation of a land feature is due to internal forces we have the categories of volcanic, folded, and faulted features. However, Hartshorne cautions against taking it as too simple a system of classification. “A system of classification could be constructed in which these various processes determine the major and minor subdivisions, but again we would have the unanswerable question of which processes are major, which are minor.”
In spite of a great difference among them all, the above three models of observation method serve the same purpose, that is, either:
- they help in searching reality for a hypothesis, or
- they help in searching reality to test a hypothesis.
Deduction is defined as - “the deriving of a conclusion by reasoning; specifically: inference in which the conclusion about particulars follows necessarily from general or universal premises.”
Several examples of landform studies that used deduction can be cited. L. C. King’s conclusions about the South African landscape are termed “extreme deductions” by Arthur Bloom. King believed that the Drakensberg scarp has retreated 250 km inland from the coast over a period of several million years. This explanation of the present scarp in question is based on observations made elsewhere and studies of several such scarps and the processes working on them. No one has actually witnessed the Drakensberg scarp standing along the shore or actually migrating inland. The most important use of the deductive method for geomorphologic studies is visualizing evolution of a landscape through time; one can imagine both how it must have looked several years ago and its probable future configuration. The general rate of steep valley walls’ retreat is calculated as 0.5 to 5.0 mm/yr by Saunders and Young. This serves as a basis for calculating the future course of modification of any such steep valley wall on the principle of deductive logic.
Unless a brief account of induction is given, discussion on deduction would remain incomplete; these are like the two sides of a coin. “Geomorphologists, like all scientists, constantly use both inductive and deductive reasoning in solving problems, usually without consciously considering the distinction.”
Induction is defined as “Inference of a generalized conclusion from particular instances. In a science like Physical Geography, inductive reasoning would involve the development of a theory to explain previously collected facts or observed phenomenon.”
Both these approaches to studying land features have shortcomings and need cautious use. If the general principle suffers from imperfection then any conclusion drawn about a specific feature on its basis would be wrong. Alistair F. Pitty remarks that because W. M. Davis’s geomorphic cycle was based on generalizations derived from only morphological evidence, with complete disregard for geological history of a region, it led to “inevitable obsolescence” of his theory for studying the south-west United States. At the time of formulation of Davisian theory the true geologic nature of the basin and range topography of this region was not known and hence could not be factored in by the cyclic erosion perspective of Davis.
Another problem with the methodologies that use present land features to visualise the past is that we cannot be certain how climate may have changed in a region. We know that the processes that influenced a region in the past may have been absolutely different from what we have at present. Here the fact that two different processes lead to similar features, that is, the phenomenon of “equifinality”, plays a crucial role in drawing a conclusion about a landform (similar forms produced by different forces are also known as ‘homology’ or ‘convergence’). A landscape full of U-shaped troughs interspersed with knife-edged ridges, for example, may be created by glaciation or by tectonic activities followed by modification by tropical agents and processes. In Fig.1.3 in case A there is a glaciated trough with seemingly no impact of faulting, while in case B the feature has been formed by down faulting of the central block and modified by weathering-mass wasting. The two, however, have the same appearance. Any deductive statement like ‘all trough-shaped valleys with steep walls and a catenary cross profile are formed by Alpine glaciers, hence the landform B in Fig.1.3 is a glaciated valley’, would be misleading.
Scope of the Geomorphology :
Geo-morphology is the study of the processes that form land-forms/landscapes.
Interestingly different scholars have described the scope of geomorphology differently. This is because they all define geomorphology in a different light. These definitions set the parameters for the nature of landform studies by geomorphologists. The dichotomy between the two great scholars, W. M. Davis and Walter Penck, elucidates this point further. Davisian system of studying landforms is “forward looking” while Penck advocated a “backward looking” approach to analyse landforms. Davis, who represents The American School, proposed a well defined system of morphological units: a sequential arrangement of these helps to understand evolution of landforms. Walter Penck, who represents the German School, on the other hand believed that landforms are a product of the competition between the crustal movements and the exogenic forces; landforms according to him should serve as a tool to understand the endogenic movements and the geologic history of the region. A synthesis of several views leads us to conclude that geomorphic studies deal with:
- Description of land forms
- Analysis of processes working on them, and
- Applied utility of the knowledge about landforms.
The three aspects have several components and a brief introduction to them may prepare the reader for the discussions in the following chapters.
Description of landforms – Description of landforms is the oldest subject matter of geomorphology; the earliest descriptive accounts are credited to geologists and geographers, there being no existence of geomorphology at that time. Accounts of landforms are available from the period when the discipline was not even defined. For example account of Japan and Siam by Varenius (1647) was prepared to help merchants engaged in trade in these regions. Later descriptions using qualitative and quantitative techniques introduced accuracy into the descriptions. Edmund Halley (1693) was one of the pioneers who prepared records of geographical distribution of physical features. He prepared records of geographical distribution of physical features. This was a period when scientists formed a part of the teams setting out on voyages. There was a demand for more accurate knowledge in stead of just a descriptive account. The description of this period focused at proving theories, for example, the exploration of a stretch of 1725 miles of the South American river Orinoco (1800) by the team of Humboldt and his companion Bonpland was not for the sake of mere collection of details but to prove the theory that river basins are separated by continuous mountain chains. We find this purpose of description reflected in the statement of Carl Ritter (1779-1859), an ardent admirer of Humboldt. The purpose is “to get away from mere description to law of things described; to reach not a mere enumeration of facts and figures, but the connection of place to place, and the laws that bind together local and general phenomena of the earth’s surface”.
The scope of studying landforms, therefore, witnessed a gradual change; needless to say it evolved as other fields of knowledge transformed and grew, especially the scientific techniques.
Understanding processes of landform evolution – It can be said that historically speaking there is a gradual evolution while academically there is a merger of the two scopes of studying landforms. It may be said that the process geomorphology took firm ground with the works of Ferdinand von Richthofen (1833-1905). He believed that description cannot be an ‘end’ by itself, but a ‘means’ to an end. An analysis and synthesis of details embodied in a descriptive account must lead to either formulation or testing of a hypothesis. Cause-effect relationship between earth environment and features formed in different areas was the scope of all studies that belong to this period. Richthofen was the first to notice that the source of the fine material deposited on Gobi region was brought by wind from far off areas. He also concluded that the rock platform in this region was a result of erosion by waves. He reached these conclusions although the two agents, wind and waves, worked upon the Gobi surface many years ago.
At present this emphasis on processes has led to development of a sub-field in geomorphology, viz., ‘Process geomorphology’; it has several sub-branches – fluvial geomorphology, karst geomorphology, coastal geomorphology and glacial geomorphology et cetera. A thorough knowledge of these processes helps us to understand the life cycle of a landform. Sometimes the features show characteristics that do not match with their current environment, indicating climatic or other geologic transformations the area must have witnessed. A student of geomorphology would be equipped to appreciate the striation marks in Deccan region of India in a correct perspective only if he has studied glacial process.
W. M Davis (Fluvial process), Ralph Alger Bagnold (Aeolian process), Robert P. Sharp (mass wasting processes) are some important process specialists’ names that the reader may come across while studying geomorphology.
Application of Geomorphic knowledge
Practical aspect of geomorphology or use of geomorphic knowledge to find answers to problems faced in a variety of fields is considered a valuable component of geomorphic studies. Important books (Principles of Geomorphology- Thornbury and Geomorphology – Chorley et al) devote sufficient space and attention to this aspect of geomorphology. The growing importance of this aspect of geomorphology has led to accumulation of such a vast and varied treasure of knowledge that this sub-field is acquiring shape of a full fledged independent science. The importance of geomorphology in managing and preventing environmental hazards, sustainable development of eco-systems, prevention of land degradation, selection of best sites for housing/dam construction etc, and locating mineral rich spots, for example is immense.
As we have seen at the out set scholars have their own understanding of what is meant by geomorphology. The consequence of this disagreement is reflected in the scope of the subject as delineated by different persons.
Wooldridge (quoted in Pitty) emphasizes exclusion of processes from the scope of geomorphology, because he thinks studying processes is the forte of physical geologists. Others like Bloom have dwelt on processes at length in their discourse of landform evolution (Bloom’s book –‘ Geomorphology: A Systematic Analysis of Late Cenozoic Landforms’). The classical example in support of processes is, of course, W. M. Davis, who proposed the invaluable formula of ‘trio’ to understand landform evolution – Structure, Process and Stage.
These differences in opinion may be confusing for a beginner but it is quite clear that these are a product of the multidisciplinary nature of geomorphology. It seems one is free to define the scope of geomorphic study as demanded by the immediate problem, the query, the model, or the level of study one is concerned with. Also the scope of study would be guided by the sub-field of geomorphology one belongs to, for example, whether the concerned landform study is done under process geomorphology, or tectonic geomorphology, or quantitative geomorphology, or megageomorphology. This variety may be seen as a healthy sign, as any growing discipline would manifest this feature.