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Dr.Sayed Zaheen Alam
Nature and Development of Geomorphology
Dr.Sayed Zaheen Alam, Assistant Professor, Department of Geography, Dyal Singh College, University of Delhi, New Delhi.
You may have been interested in Geomorphology, but without knowing it. Probably you have seen the mountains like Himalayas or the Juhu beach in Mumbai. In these places you may have noticed that some processes are changing the landscape although with varying intensity. Like for example in India if you visit from Kanyakumari to Kashmir or Jaisalmer to Arunanchal Pradesh you will find remarkable variation in the relief features.
Figure: Diversity in the Relief
This may tempt you to question why it is like this? i.e., why there is diversity in the relief features of the earth’s surface? In the present module we are going to take you on a journey of science of landscape that is known as Geomorphology, but before that let us see the place of geomorphology in Geography. We know that ‘Physical Geography’ is the base of geography ‘it unifies several branches of natural sciences for the purpose of understanding the relationship of man to his environment’ (Strahler). We can also consider geomorphology as the base of physical geography. We know that geography is concerned to provide accurate, orderly rational description of the variable character of the earth’s surface. The focus of geomorphology is also the‘surface of the earth’.Therefore we can say that it is one of the most important branche of geography under the banner of physical geography.
In the present module we are going to cover about following aspects of geomorphology:
1. Definition of Geomorphology
2. Organization of the Subject Matter
3. Relationship of Geomorphology with other Subjects
4. Historical Development
4.1 Modern Geomorphology and the Age of Hutton and Lyell in Europe
4.2. Founders of Modern Geomorphology in America
5. Recent Trends in Geomorphology
6. Geomorphology: SWOC analysis
1. Definition of Geomorphology
A geomorphologist attempts to formulate answers to following questions: What is a landform? What makes one landform unique from another? How are different landforms associated with each other? Are they arranged in sequential order? How do landforms evolve? How they may evolve in the future? Likewise what is the significance of geormorphic knowledge for human society?
The word Geomorphology is derived from three Greek words i.e., Ge (the Earth), Morphe or Morphi (forms) and Logos (discourse):
Therefore geomorphology represents ‘a discourse on Earth Forms’. In order to understand the meaning of Geomorphology let us ponder over some basic definitions given by the well known geomorphologists.
According to Worcester (1949), the “Geomorphology is the interpretative description of the relief features of the Earth”. The term relief covers the physiography of an area such as differences in altitude size and shape of the valley, forms and steepness of different slopes. Therefore geomrphologistsare basically concerned with relief features of the Earth.
According to Bloom (1992) the geomorphology deals with “the systematic description and analysis of landscapes and the processes that changed them”. Bloom added an important aspect in the definition of Geomorphology i.e., ‘Processes’ responsible for changing the landscapes. It should be noted that the nature and intensity of different processes vary from region to region. These different erosional agents often produce an orderly sequence of landform on the surface of the Earth. The task of the geomorphologist is to scientifically explore and systematically arrange the landforms in these orderly sequences. That is why perhaps Thornbury (1993) said Geomorphology “is the science of Landforms it also includes submarine landforms”. Let ussee why it is considered as the science of Landforms? We know aim of the science is to explain what happens in the world. A famous philosopher of Science Hempel suggested that scientific explanations typically have the logical structure of an argument, i.e. a set of premises followed by a conclusion. He further said that if the explanation were spelled out in full detail, the law would enter the picture (S.Okasha 2002). Therefore in general we can say that science beliefs in observation, reasoning (like inductive and deductive), empirical testing, empirical measurements, generalizations, systematic study of any phenomenon and the formulation of laws. All these attributes are also present in geomorphology in one or the other forms. For example, Principle of Uniformitarianism (Hutton 1785) is a great underlying principle of modern Geomorphology and Geology. Similarly field observation and measurement is also a part of Geomorphology. For Example,H. F. Reid of Johns Hopkins University conducted a field study following the great 1906 San Francisco earthquake. On the basis of field observation he proposed ‘Elastic Rebound Theory’. Likewise,American geomorphologist W.M Davispresented a general theory of landform development that is popularly known as ‘Cycle of Erosion’. His cycle of erosion was based on careful field observations. Therefore by nature geomorphology is concerned with science of landforms.
Did You Know?
The term Geomorphology in modern sense was probably used by Keith in the year1894.
2. Organization of the Subject Matter
In the modern world the raisen d’etre of any discipline is its subject matter and its usefulnessfor the society. The Subject matter of Geomorphology incorporates Structure, Process, systematic analysis and evolution of Landforms. Let us discuss in detail about the subject matter of geomorphology.
(a) The first thing a geomorphologits wants to know is about the terrain i.e.,what is the structure?
The term structure denotes an arrangement of interrelated elements in a material object or system. In geomorphology it means (i) Lithology of the rock such as porosity, relative permeability, folding and faulting; (ii) Stratigraphic arrangement of the rock; (iii) Constitution or composition of the rock and(iv) Variation in the relief features of the continents and Ocean basins.The nature and character ofstructures are mainly determined by endogenic or internal forces. We shall study in detail about these forces in other modules of present paper.
(b) The second term or concept i.e.,process in geomorphology is mainly related to external or exogenic forces. These forces contribute to shape a landscape. They are also called destructional processes or denudational processes. A brief list of these endogenic and exogenic processes are as follows:
It is important to note that geomorphic processes vary in intensity from one region to another. These variations are mainly attributedto differences in climate, vegetation, and altitude. The rate of these forces vary from a few centimeters per thousand years for surface weathering of ancient monuments to 50 meters/second or more for an avalanche (Bloom).
(c) In the systematic analysis of landforms, agemorphologist seeks to classify landforms on the basis of scale of relief features, genesis and evolution of landforms. It should be noted that one of the fundamental principles of geomorphology states that “as the different erosional agents act upon the earth’s surface there is produced an orderly sequence of landforms. Therefore we can classify landformson in one of the following categories:
(i) Generic Classification of Landforms: Description of entire group or class of landforms i.e., Mountain Plateau and Plains. For example Himalayan mountain ranges, Tibetan Plateau and the Northern plains in India
(ii) Genetic Classification of Landforms: It means classification of landforms by dominant set of geomorphic processes. For example, Tectonic landforms, fluvial landforms, Karst landforms, Aeolian landforms, Coastal landforms and Glacial landforms.
(iii) We can also classify the landforms on the basis of their scale and lifespan
For example the present graph shows the systematic arrangement of landforms on the basis of their scale and lifespan. On ‘X’ axis the areal coverage of landform is shown in square kilometers and on ‘Y’ axis average lifespan of each landform is shown in years. For example average lifespan of “pool” that is a small landform found in the floodplain has a lifespan of around 10 years on the other hand on top of the graph the ‘major drainage basins’ having almost entire group of landforms (mainly shaped by river activity) has a lifespan of more than 10 million years. The graph also reveals that the areal coverage of former less is than 0.25 square kilometer and thecoverage of later is more than 1 million square kilometers.
iv) If we take only scale as the basis for the classification of landforms, we can rearrange the earth’s landforms into three different orders: for example, Relief Feature of First order, it includes Continental Platforms and Ocean Basins. Similarly on next level of hierarchy II order landforms are grouped. The relief features of the second order are superimposed on First order category of landforms. For example, Plains, Plateau and Mountains. The last order i.e.,III order relief features are superimposed on II order relief features such as Valleys, Canyons and Dunes.
3. Relationship of Geomorphology with other Subjects
Contemporary geographers classify geomorphology (as a branch of geography) under the Earth Science Group.
The present figure demonstrates that several other branches of knowledge are directly and indirectly linked with geomorphology. These allied disciplines are having a kind of mutual relationship with geomorphology. For example, according to Spark(1960)‘the main contribution of geomorphology to geology is in unraveling of geographical successions, for example when deposits are thin and scattered such conditions being most characteristic of Pliocene and Pleistocene periods in certain areas’. Similarly geomorphologists must have good working knowledge of geology since without knowing lithology of rock geomorphologist cannot fully understand the formation and character of landform. One of the fundamental principles of geomorphology also states that “Geological structure is a dominant control factor in the evolution of land forms and is reflected in them”. Likewise meteorology provides information related with effect of climatic elements on the rate and nature of geomorphic processes. In turn geomorphology contributes to meteorology by disclosing effect of morphology on climatic variables. For example, the rainfall during the Monsoon season in India is largely affected by the orographic effect of Himalayas. On the other hand it is equally true that “an appreciation of world climates is necessary to a proper understanding of the varying importance of the different geomorphic processes.” (Thornbury, 1993)
- Historical Development
According to Summerfield (1991) the way geomorphologists approach the study of landforms at present time can only be seen in proper context if we appreciate how central concepts of geomorphology have been developed. We can trace the development of Geomorphological ideas into well marked four periods of history i.e., (i) Ancient Period and Medieval period; (ii) Modern Geomorphology and the Age of Hutton and Lyell in Europe (iii) Founders of Modern Geomorphology in America and; (iv) the recent trends
The early writings related with landforms can be traced to the times of early Greek, Roman, Arab and Chinese thinkers. For example,the father of History Herodotus (484-425 B.C.) once said “Egypt is the gift of the River (Nile)”. Therefore, he attributed the formation of Nile river delta to the accumulation of river born silt (Kale and Gupta, 2001). The Aristotle (384-322 B.C.) as pioneer of inductive reasoning talked about ‘origin of springs’. The Arab civilization during the medieval period also contributed to the development of geomorphology. Abdullah Ibn Sina sometimes known in the West by Latin name, Avicenna introduced the concept of “differential erosion”. He used this term to describe formation of valleys and the altitude of mountains. According to Thornbury (1993) “a work by a group of unknown Arabic scholars known as ‘The Discourses of the Brothers of Purity’ (941-982 A.D.)” discussed about erosion and transportation by streams and wind, weathering and even embryonic idea of pneneplanation. Thereafter during the renaissance Leonardo da Vinci(1452-1519) discussed about the formation of valleys by river erosion and presence of marine fossil shells in mountain. The Frenchman Buffon (1707-1788) also discussed erosive power of stream till sea level.
4.1 Modern Geomorphology and the Age of Hutton and Lyell in Europe
A paper presented by Hutton in the year 1785 before the ‘Royal Society of Edinburgh’ changed the discourse of the history of Earth’s formation. Hutton proposed that landsurface is evolved by slow, unremitting erosive power of moving water (Summerfield).He also challenged the religious viewpoint of a particular faith about the formation of the Earth. Hutton is best known for his two statements:(i) The present is the key to the past and , (ii) No vestige of a beginning no prospect of an end. Thus he established the principle or doctrine of Uniformitarianism. His idea about the ‘Theory of Earth’or formation of earth was more popularised by John Playfair (1748-1819) and Sir Charles Leyell (1797-1875). Leyelllater became the great follower of uniformitarianism in Europe.His book ‘Principles of Geology’ was based on Hutton’s principle of Uniformitarianism.
The discovery of Pleistocene Ice Age by Louis Agassiz (1807-1873) in Europe and the genetic classification of landscape by Arthur Penk (1894)also created sufficient knowledge base for the development of physographic geology in Europe. Later Alfred Lothar Wegener in 1912 – a 32 year old lecturer in meteorology and astronomy in Germany propounded the Continental Drift theory.
Figure: Alfred Lothar Wegener (1880-1930), Propounded Continental Drift theory.
Figure: Pangaea Surrounded by Panthalassa during Upper Carboniferous Period.
This theory was based on sound scientific evidences which ultimately gave birth to the plate tectonic theory.Todayplate tectonic theory is of a great significance in understanding of the global distribution of earthquakes, volcanoes and identification of disaster prone areas. We will also study this theory in detail in a separate module of the present paper.
4.2 Founders of Modern Geomorphology in America
The period between 1875 and 1900 are considered as “the heroic age in American geomorphology” (Thornbury, 1993). The champions of this period were Major J.W.Powell (1834-1902), G.Gilbert (1843-1918) and the C.E. Dutton (1841-1912).
Powell is known for the concept of ‘base level’ i.e., a level below which the dry lands cannot be eroded. The present laws of landscape development are built around Gilbert’s dynamic equilibrium mechanism. Gilbert also attempted to develop quantitative approachin geomorphology. The purpose of his quantitative approach was to explainthe relationship between stream load, volume and velocity of water vis a vis gradient factor. Dutton applied the concept of ‘base level’ to analyse the ‘Great Denudation’ in Colorado Plateaus area in United Sates of America. W.M. Davis (1850-1934) associated with Harvard University quickly grasped the idea of ‘base level’ given by Powell, great denudation discovered by Dutton and the quantitative approach proposed by Gilbert. On the basis of their ideas Davis proposed the ‘cycle of erosion’. He described the evolution oflandforms in terms of structure, process and time.
It should be noted that W.M. Davis theory was extremely popular in geomorphology for a long time, but it was ultimately superseded by new datasets and the development of plate tectonic theory (Goudie and Viles, 2010). We shall study geomorphic cycle and plate tectonic theory in separate modules of present paper.
5. Recent Trends in Geomorphology
The present day geomorphologists are largely influenced by two important revolutions occurred in the discipline of Geography i.e., ‘Quantitative revolution’ and the ‘Process revolution’. The former introduced explicit emphasis on the use of scientific methods and later developed the greater understanding of the processes responsible for the creation of variable character of the earth surface.
The measurement, monitoring, analysis and modelling of the formative processes have become integral part of present day geomorphology. For example, Differential GPS (or DGPS) is now commonly used by geomorphologists to identify precise location of topographical features. This prices measurement is also extremely useful for the changes happening in the glacier areas especially to monitor climate change. It is equally helpful for the identification of hazards related with landslides and slope failures. The Ground based Light Detection and Ranging (LIDAR) is another instrument to identify precise location of third order landforms especially in inaccessible areas of the earth. The modern day sensitive instruments can even track the relative movement of different plates, glaciers as well as lava flow in a volcanic region.
The high resolution satellite imageries, Computer aided Cartography, Electronic Distance Measurement (EDM), Global Positioning System (GPS) and GIS softwares haveimmensely contributed to the development of a new specialized branch of geomorphology i.e., Geomorphometry.
Now within a fraction of a second gemorphologists can compute topographic elements through Digital Elevation Models (DEMs) and Digital Terrain Models (DTMs).
The freely available Google Earth satellite imageries have given new tool to explore the inaccessible parts of the world. Now a volcanologist can virtually explore an active volcano through the near real time satellite imageries. For example the present imagery is showing an areal view of a crater at the summit of Mt St. Helens (USA).This image has been taken by satellite.
Figure: Areal view of a crater at the summit of Mt St. Helens (USA). Image credit: ©Google earth 2015).
A wealth of data on the quantities of sediments found in the deep sea basins of the planet earth by ‘Integrated Ocean drilling project’ has lured several young researchers to go deep into the field of geomorphology or specifically oceanography. The drilling projects have also contributed to applied geomorphology. For example identification of oil exploration sites require application of geomorphic knowledge. The use of geomorphic knowledge to find answers to the problems faced by human beings is called ‘applied geomorphology’. For example geomorphicknowledge is prerequisitefor managing and preventing natural hazards, land resource planning, Environmental Impact Assessment, site suitability analysis for House, Industry and dams.It is more advantageous that we know, for instance, something of the discharge and sediment load of streams, than they are ‘young’ or ‘mature’, as Davis described them (Bryant, 1992). We will also attempt to discuss applied geomorphology in separate module of this paper. At present with the advent of the internet and improved access to many sources, the research literature in geomorphology has increased rapidly. In 2013 alone, the Journal of Geomorphology published 369 research papers, most of a highly technical nature (Gregory and Lewin, 2014).
6. The State of Geomorphology: SWOC analysis:
Let us see the state of geomorphology through SWOC analysis i.e., Strength, Weaknesses, opportunities and challenges:
Geomorphology: Strength and Opportunities
Geomorphology is enriched with well developed fundamental concepts. There is no dearth of books related to geomorphology.
(b) Geomorphology is scientific in nature. The techniques like EDM, GPS and GIS, Numerical Analysis and Laboratory analysis of rocks and sediments, and several instruments used in filed investigations makes scientific identity of the discipline.
(c) Several developments in the field of science and technology has opened many specialized branches of geomorphology such as, remote-sensing geomorphology, experimental geomorphology, extraterrestrial (planetary) geomorphology, engineering geomorphology and anthropogenic-geomorphology. One can also become an expert in these branches. For example,
Fluvial Geomorphologist,Karst Geomorphologists, Coastal Geomorphologists, Biogeomorphologist, Tropical Geomorphologist, Mountain Geomorphologist. The applied geomorphology also offers many job opportunities in specialized fields. For example,expert in disaster management, EIA expert and Environmental Specialist.
Geomorphology: Weaknesses and Challenges
Geomorphology requires a rigorous understanding of the fundamentals concepts of the discipline. It is basically a heterogeneous science; therefore it requires expertise in various filed of sciences. The instruments required for geomorphometric analysis are very costly. Therefore, the field work is very expensive. Thisbranch of physical geography hasalso not captured the interest of general public except in case of random news events related to volcanic eruptions and earthquakes. Recent massive 7.9 magnitude shallow focus Nepalearthquake on 25, April, 2015 at 11.48 AM (IST) hasshocked the world. It claimed the life of more than 9,000 people in our neighboring country Nepal, which is one of the worst in Nepal’s history. Nepal is still coping with the aftermath of the earthquake. Therefore geomorphic literacy is extremely important not only to understand the phenomena but also for disaster. We will also study in detail about the earthquakes and geomorphic hazards in different modules of present paper.
Thank you
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References
- Okasha,S., 2002:Philosophy of Science A very Short Introduction, Oxford University Press, New York. pp-41
- Spark, B.W.,1960:Geomorphology, Longman, New York, pp-4
- Summerfield, M.A:1991: Global Geomorphology an Introduction to the Study of Landforms, Longman, New York, pp 3-4
- Kale, V.S., and Gupta, A., 2001:Introduction to Geomorphology, Orient Longman, pp 1-13
- Thornbury, W.D., 1993:Principles of Geomorphology, Second Edition, Wiley Eastern Limited, New Delhi, pp-1-33
- Bloom, A.L.,1991: Geomorphology a Systematic Analysis of Late Cenozoic Landforms, Second Edition, PHI, New Delhi, pp-1-16
- Gregory, K.J. and Lewin, J., 2014:The Basics of Geomorphology, Sage, California, pp-2
- Goudie, A and Viles, H., 2010:Landscapes and Geomorphology A Very Short Introduction, Oxford University Press, New York.
- Bryant, R.H., 1992:Physical Geography, Rupa and Co, Delhi.
- Szabo, J, David, L and Loczy, D., 2006:AnthropogenicGeomorphology A Guide to Man-Made Landforms, Springer, New York
- Huggett, R.J., 2007: Fundamentals of Geomorphology, Second Edition,Routledge, New York, pp 3-29