Basic Concepts of Geomorphology | Geology Optional Notes for UPSC PDF Download

Geomorphology

Geomorphology deals with characteristics of the Earth’s surface and all geological processes that try to change it over a period of time. Geomorphology is based on some fundamental concepts, which have developed over a long period of time. These concepts not only provide basic fundamental components of geomorphology but also provide a glimpse of the breadth and scope of the subject. These concepts deal with the underlying principles of landform and landscape characterisation, controlling factors, development and evolution, and constraints (both spatial and temporal) on geomorphic evolution. Due to its importance, geomorphological data has applications in various aspects of development, planning, and environmental management.

Definition

• Geomorphology (Greek words- geo meaning Earth, morphē meaning forms and logus meaning description) is considered as description of surface morphology of the Earth.
• Physiography embodies in its study the landform description, covering only the basic notions of variations of the Earth’s surface based on differences in relief.
• Physical geography deals with the description of surface variations and landforms primarily from the point of view of their applicability for use by humans.
• Geomorphology includes the study of landforms, their development, responsible processes and their evolution with time.
• Various definitions given by geologists include interpretations such as "interpretative description of the relief features of the Earth", "analysis of the origin and evolution of Earth features", and "the science of landforms including the submarine topography".

Landform and Landscape

• Landform is the fundamental geomorphic unit in the landscape of an area.
• Landscape is the sum total of all the landforms occurring in an area.
• Examples include fluvial landscape comprising fluvial landforms like channels, floodplains, and bars; coastal landscape consisting of coastal landforms like beaches, mudflats, and lagoons; glacial landscape made up of glacial landforms, etc.
• Geomorphological studies can be carried out on various scales from local to regional to continental, and planetary scales.

Landscape Evolution

• Landforms and landscapes evolve over variable time scales from tens of years to thousands or millions of years.
• Reconstructing the formation, modification, and development of landscape over geological time is termed as landscape evolution or geomorphic evolution.

Scope

• The scope of geomorphology encompasses the study of landforms and landscapes, geological processes, evolution, and dynamics of geomorphic changes at spatial as well as temporal scales.
• The ultimate aim of geomorphology is to reconstruct landscape evolution through geologic time.
• Parts of geomorphology overlap with several other branches of geology including sedimentology, stratigraphy, structural geology, petrology, hydrology, tectonics, marine sciences, and geoarchaeology.
• The diversity of data enhances the utility and application of geomorphology in a variety of fields.
• Geomorphology has the widest scope amongst all other branches of geology, which also means that it has application in a wide variety of fields.

Development of Geomorphological Concepts

• In the previous section, various definitions of geomorphology were introduced. Now, we delve into the development of geomorphological concepts. The knowledge of the Earth’s surface has evolved throughout human existence, with significant advancements occurring particularly in the last few hundred years. This development partially overlaps with the principles of stratigraphy, notably Charles Lyell's principle 'Present is the key to the past'. 
• The principles of stratigraphy, including order of superposition, uniformitarianism, and biostratigraphic zonation, greatly influenced our understanding of landscapes and the foundational concepts of geomorphology. Further development occurred with the introduction of the Davisian cycle of erosion and increasing knowledge of geological processes, including surface processes.

Fundamental Concepts

• The Principle of Uniformitarianism: This principle, slightly modified by Thornbury from Hutton's original idea, asserts that the same physical processes and laws that operate today have operated throughout geological times, albeit not always with the same intensity. It underlies the uniformity of geomorphic processes through geological time, which operate with different intensities at different times.
• Role of Geologic Structure: This concept highlights the dominant role of geological structures in the evolution of landscapes. Geological structures such as fault zones, folds, and joints affect the variability and susceptibility of rocks to geomorphic processes, leading to the development of landforms and landscapes correlated with these structures.
• Distinctive Imprints of Geomorphic Processes: Different geomorphic agents produce their own characteristic assemblage of landforms. Each geomorphic process results in the formation of distinct landforms, allowing for the identification and characterization of these processes based on their unique characteristics.
• Orderly Sequence of Landforms: As erosional agents act upon the Earth's surface, they produce an orderly sequence of landforms with distinctive characteristics at different stages of development. This concept emphasizes the role of erosion in shaping landscapes over time, leading to a sequential development of landforms.
• Complexity in Geomorphic Evolution: Geomorphic evolution is often complex, with multiple factors such as climate, tectonics, and sea-level changes interacting to influence landscape development. Understanding geomorphic evolution may be challenging due to the interplay of these factors.
• Age of Earth's Topography: Most of the Earth's topography is no older than the Pleistocene epoch, with little of it older than the Tertiary period. This concept has implications for understanding the age of landscapes, suggesting that the majority of the Earth's surface has been continuously modified by geomorphic processes.
• Importance of Pleistocene Influences: The Pleistocene epoch played a significant role in shaping present-day landscapes through its extreme climatic changes. Understanding the geological and climatic changes during this period is essential for correctly interpreting landscape evolution.
• Role of World Climate: Different climatic zones on Earth are characterized by distinct geomorphic processes, leading to the formation of different landform assemblages. A thorough understanding of world climate and related geomorphic processes is crucial for interpreting past landscapes.
• Historical Extension in Geomorphology: Geomorphic studies should extend back in geological time to delineate landscape evolution fully. This involves interpreting the past geological history of landforms and landscapes to understand their development over time.
• Differential Rates of Geomorphic Processes: The Earth's surface possesses relief due to differential rates at which geomorphic processes operate. Variations in erosion rates lead to the formation of varied relief features, with some areas experiencing faster erosion than others.

Uniformitarianism and Catastrophism

• Uniformitarianism: This theory posits that the processes operating on the Earth's surface have been consistent throughout geological time. It emphasizes the uniformity of processes in the present and the past, aiding in estimating geological time and dismissing notions of a young Earth.
• Catastrophism: In contrast, catastrophism suggests that the Earth has been shaped primarily by abrupt, short-lived, and worldwide events. This theory, proposed by Georges Cuvier, attributes geological changes to catastrophic events, such as floods, rather than uniform processes.

Scale in Geomorphology

• Spatial and Temporal Scales: Geomorphological studies vary in spatial extent and temporal duration. Spatial scales range from microscale investigations of specific river channels to planetary-scale studies of extraterrestrial surfaces. Temporal scales encompass short-term events like floodplain deposition to long-term processes spanning millions of years.

Concept of Geomorphic Cycle

Let's explore the concept of geomorphic cycle, which explains the evolution of landscapes over time. This theory, also known as the cycle of erosion or Davisian theory of landscape evolution, was first proposed by William Morris Davis in the late nineteenth century. The geomorphic cycle describes landscape evolution through a series of stages, ultimately culminating in the formation of a peneplain, which is a low-relief, almost flat landscape.

• Introduction: The geomorphic cycle encompasses the major stages of youth, maturity, and old age in landscape evolution. It assumes the initiation and persistence of tectonic uplift throughout the cycle, along with uniform lithology.
• Stages of the Cycle: The cycle comprises six stages, starting with a low-relief peneplain and progressing through youth, maturity, and old age, ultimately returning to a peneplain.
• Role of Tectonic Uplift: Tectonic uplift initiates erosion of the landscape, with rivers as main agents. The landscape modification typically begins in river valleys.

Stages of the Geomorphic Cycle

• Early Youth: In this stage, rivers erode their valleys downward, creating broad and flat uplands with deep river valleys.
• Late Youth: Vertical erosion continues, accompanied by some lateral erosion of valleys. The landscape features predominantly valley slopes.
• Maturity: Continued tectonic uplift and erosion lead to highly erosional landscapes, with broad valley floors and subdued relief.
• Late Maturity: Prolonged erosion results in low relief and almost flat peneplains, devoid of high elevations.
• Renewed Uplift: Following the old stage, renewed tectonic uplift can initiate a new geomorphic cycle, leading to the production of a polycyclic landscape.

Advantages of the Geomorphic Cycle Concept

• Recognition of Geologic Time: The concept acknowledges the importance of geologic time in landscape evolution, with cycles potentially lasting tens of millions of years.
• Sequential Framework: It provides a sequential framework with well-defined stages—youth, mature, and old—to reconstruct the progressive changes in landscape.
• Significance of Tectonics: The cycle recognizes the significance of tectonics as a causative factor for large-scale erosion, particularly in active tectonic regions.

This concept is valuable in understanding long-term landscape evolution and has practical applications in regions located in active tectonic zones.