Earth’s surface is not stable but is constantly changing. None of the landforms found on the earth’s surface are forever. There are various geomorphic processes working on the landforms. These processes were working in the past and also working presently, though with varying degrees and intensity.
The earth’s crust is influenced by internal and external forces, which may affect the earth on a major and minor scale. Internal forces may include upliftment, contraction, expansion, disruption, distortion and outpouring. External forces would include forces of denudation like weathering and erosion.
The description of the landforms cannot be explained only through these forces since these changes are so slow that they go unnoticed. But we can observe and notice these changes when these changes are sudden, like volcanic eruptions, landslides and earthquakes. The present landforms are a manifestation of the complex and intricate interaction of earth’s material facing resistance on the one hand from tectonically- and climatically-derived forces.
Earth Movements
As we know, the earth’s crust is constantly affected by internal forces. The main causes of such internal forces can be the radioactivity originating within the deep interiors of the earth’s crust or substratum and the resultant convection currents caused by it. These convection currents cause the crust to move, which further causes sudden and rapid movements like earthquakes or extremely slow movements like mountain building and continental building, which may take millions of years.
These movements can cause upliftment, warping, turning, twisting, tilting, fracturing, subsidence and distortion of crust, and some may even cause squeezing of the rocks, which would give rise to high mountain ranges.
Type of Earth Movements
There are broadly two kinds of forces that cause the earth’s movements. They are as follows:
Exogenetic / Exogenic / Epigene Forces
Exogenetic is mostly destructive forces, which through various processes, would try to change the various relief features on the earth’s surface by smoothening, carving and moulding these features.
Endogenetic / Endogenic / Hypogene Forces
(In Greek, ‘endo’ means within and ‘genera’-origin) Endogenetic forces can give rise to various structural features on the earth’s surface related to upliftment and subsidence, folding, faulting, fracturing and volcanic eruption. All the landforms and relief features found on the earth are formed from the earth’s materials. Landforms are formed because various geomorphic processes operate on and beneath the earth’s surface at a differential rate. The exogenetic processes derive their energy from Earth’s internal (endogenetic), which gives mobility to the Earth’s crust (tectonism) and from climate, which takes further help from the sun, which is its driving force.
Endogenetic movements can be of two types-
- (i) Diastrophic and
- (ii) Sudden movements
In Greek, ‘diastropos’ means turned, twisted and distorted. Diastrophic forces are the ones that generally originate from deep beneath the earth’s surface and act as a vertical force, and work against exogenetic forces like gradational processes. They disrupt the process of reducing the earth to the sea level by forming various landform features on it.
Diastrophic forces can be classified into three categories–
- (i) Tectonic
- (ii) Isostatic
- (iii) Eustatic
Within diastrophic forces, Tectonic (In Greek, ‘tekton’ means builder) is the most commonly used word as it has wide connotations. Tectonic movements can be Epeirogenic Movements and Orogenic Movements. These energy forces which emanate from within the earth’s crust include nop-isostatic or crustal warping within the mantle (which is called epeirogenesis), earthquakes, folding (which is mountain building or orogenesis), faulting, metamorphism due to heat flow and vulcanism.
Endogenetic processes receive less importance in geomorphological studies. But these forces are increasingly gaining importance and appreciation because of the effects of such movements in certain areas of the world, such as the circum-Pacific belt and areas of the young-fold Mountain. They are expressed and studied for the earthquake activity and vulcanicity in the said areas and their important influences on such areas.
In areas where the endogenetic influences are more powerful, the changes brought by the exogenetic processes can be altered. Gilbert had defined epeirogeny as the process of continental building, and in parallel to this, he had defined orogeny as the process of mountain formation. These two sets of processes differ enormously in space and time scales.
In many regions of the earth where the vertical crustal movements are very slow and are measured in millimetres per year (1 mm/yr = 1 m/1000 yrs. = 1 km/million yrs.) have persisted throughout late Cenozoic time, the rate of cumulative uplift has outpaced erosional lowering. Such tectonic geomorphology is associated with the construction of the landscapes. These are regions of erosional landscapes in which the tectonic origins are still obvious.
Fig. shows a chart which explains the division of the major earth movements.
Read More in Geomorphology
- Earth Movements: Meaning and Types
- Epeirogenic Earth Movements
- Orogenic Earth Movements
- Cymatogenic Earth Movements
- Concept of Stress and Strain in Rocks
- Folds in Geography
- Fault in Geography
- Mountain Building Process
- Morphogenetic Regions
- Isostasy: Concept of Airy, Pratt, Hayford & Bowie and Jolly
- Continental Drift Theory of Alfred Lothar Wegener (1912)
- Plate Tectonics: Assumptions, Evidences, Plate Boundaries and Features Formed
- Volcanoes: Process, Products, Types, Landforms and Distribution
- Earthquakes: Processes, Causes and Measurement
- Plate Tectonics and Earthquakes
- Composition and Structure of Earth’s Interior
- Artificial Sources to Study Earth’s Interior
- Natural Sources to Study Earth’s Interior
- Internal Structure of Earth
- Chemical Composition and Layering of Earth
- Weathering: Definition and Types
- Mass Wasting: Concept, Factors and Types
- Models of Slope Development: Davis, Penck, King, Wood and Strahler
- Davis Model of Cycle of Erosion
- Penck’s Model of Slope Development
- King’s Model of Slope Development
- Alan Wood’s Model of Slope Evolution
- Strahler’s Model of Slope Development
- Development of Slope
- Elements of Slope
- Interruptions to Normal Cycle of Erosion
- Channel Morphology and Classification
- Drainage System and Drainage Pattern
- River Capture or Stream Capture
- Stream Channel Pattern
- Fluvial Processes and Landforms: Erosional & Depositional
- Delta: Definition, Formation and Types
- Aeolian Processes and Landforms: Erosional & Depositional
- Desertification: Definition, Problem and Prevention
- Glacier: Definition, Types and Glaciated Areas
- Glacial Landforms: Erosional and Depositional
- Periglacial: Meaning, Processes and Landforms
- Karst Landforms: Erosional and Depositional
- Karst Cycle of Erosion
- Coastal Processes: Waves, Tides, Currents and Winds
- Coastal Landforms: Erosional and Depositional
- Rocks: Types, Formation and Rock Cycle
- Igneous Rocks: Meaning, Types and Formation
- Sedimentary Rocks: Meaning, Types and Formation
- Metamorphic Rocks: Types, Formation and Metamorphism
- Morphometric Analysis of River Basins
- Soil Erosion: Meaning, Types and Factors
- Urban Geomorphology: Concept and Significance
- Hydrogeomorphology: Concept, Fundamentals and Applications
- Economic Geomorphology: Concept and Significance
- Geomorphic Hazard- Earthquake: Concept, Causes and Measurement
- Geomorphic Hazard- Tsunami: Meaning and Causes
- Geomorphic Hazard- Landslides: Concept, Types and Causes
- Geomorphic Hazard- Avalanches: Definition, Types and Factors
- Integrated Coastal Zone Management: Concept, Objectives, Principles and Issues
- Watershed: Definition, Delineation and Characteristics
- Watershed Management: Objective, Practice and Monitoring
- Applied Geomorphology: Concept and Applications