Concept of Stress and Strain in Rocks

Understanding the concept of stress and strain is mandatory to comprehend different types of crustal deformations. For a layman, stress may denote an activity related to pushing and pulling. Similarly, strain is considered as deformation in the form of bending, breaking, and stretching. But technically, both terms have a deeper meaning. Let us understand the meaning of stress and strain in the context of geomorphology.

We know that force (F) is a definable vector quantity that changes or tends to produce a change in the body’s motion (Billings, 2016). Since the force is defined by its magnitude and direction (vector quantity), it may be expressed by an arrow. In structural geology, a force applied to material that tends to change the material’s dimension is called stress.

The Figure shows that in mathematics, the Stress is represented by the σ meaning sigma, defined as the force (F) per unit area (A), or σ = F/A. Therefore, we can consider stress as the intensity of force or a measure of how intense a force is. The effect of stress on rocks or any other material is called strain. Therefore, the strain represents deformation caused by stress. The deformation can be in the form of dilation and distortion:

• Dilation: The figure shows that the Strain resulted in a volume change called dilation.

• Distortion: On the other hand, the figure shows that the distortion denotes a change in form, volume, or both.

There are three types of stress, i.e.,

1. Tensional,
2. Compressional, and
3. Shear.

Tensional Stress:

It is clear from plate tectonics that tensional stress is produced along the divergent plate boundary. The following diagram can show it. The diagram shows that a rectangular rock body is under tension when subjected to external forces that tend to pull it apart. It is a stretching stress that can potentially increase a material’s volume.

Compressional Stress:

The Plate tectonic theory reveals that convergent boundaries create compressional stress. The figure shows that a rectangular rock body is said to be under compression when it is subjected to external forces that tend to compress it. Therefore, compression tends to decrease the volume of the material but under certain conditions or up to a certain limit.

Shear Stress:

In the case of transform plate boundaries, shear stress is produced. The figures show that shear stress changes the shape of the rock material.

Strength of Rocks

It is also important to note that rupturing, distortion of rocks or deformation also depends on the strength of the rock. The laboratory test reveals that rocks respond to compression, shear, and tensile strength. Accordingly, we classify the rock material as brittle and ductile.

In this regard, it is important to note that rocks may break under less pressure conditions at the surface under intense tensional or compressional stress.

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2. Epeirogenic Earth Movements
3. Orogenic Earth Movements
4. Cymatogenic Earth Movements
5. Concept of Stress and Strain in Rocks
6. Folds in Geography
7. Fault in Geography
8. Mountain Building Process
9. Morphogenetic Regions
10. Isostasy: Concept of Airy, Pratt, Hayford & Bowie and Jolly
11. Continental Drift Theory of Alfred Lothar Wegener (1912)
12. Plate Tectonics: Assumptions, Evidences, Plate Boundaries and Features Formed
13. Volcanoes: Process, Products, Types, Landforms and Distribution
14. Earthquakes: Processes, Causes and Measurement
15. Plate Tectonics and Earthquakes
16. Composition and Structure of Earth’s Interior
17. Artificial Sources to Study Earth’s Interior
18. Natural Sources to Study Earth’s Interior
19. Internal Structure of Earth
20. Chemical Composition and Layering of Earth
21. Weathering: Definition and Types
22. Mass Wasting: Concept, Factors and Types
23. Models of Slope Development: Davis, Penck, King, Wood and Strahler
24. Davis Model of Cycle of Erosion
25. Penck’s Model of Slope Development
26. King’s Model of Slope Development
27. Alan Wood’s Model of Slope Evolution
28. Strahler’s Model of Slope Development
29. Development of Slope
30. Elements of Slope
31. Interruptions to Normal Cycle of Erosion
32. Channel Morphology and Classification
33. Drainage System and Drainage Pattern
34. River Capture or Stream Capture
35. Stream Channel Pattern
36. Fluvial Processes and Landforms: Erosional & Depositional
37. Delta: Definition, Formation and Types
38. Aeolian Processes and Landforms: Erosional & Depositional
39. Desertification: Definition, Problem and Prevention
40. Glacier: Definition, Types and Glaciated Areas
41. Glacial Landforms: Erosional and Depositional
42. Periglacial: Meaning, Processes and Landforms
43. Karst Landforms: Erosional and Depositional
44. Karst Cycle of Erosion
45. Coastal Processes: Waves, Tides, Currents and Winds
46. Coastal Landforms: Erosional and Depositional
47. Rocks: Types, Formation and Rock Cycle
48. Igneous Rocks: Meaning, Types and Formation
49. Sedimentary Rocks: Meaning, Types and Formation
50. Metamorphic Rocks: Types, Formation and Metamorphism
51. Morphometric Analysis of River Basins
52. Soil Erosion: Meaning, Types and Factors
53. Urban Geomorphology: Concept and Significance
54. Hydrogeomorphology: Concept, Fundamentals and Applications
55. Economic Geomorphology: Concept and Significance
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57. Geomorphic Hazard- Tsunami: Meaning and Causes
58. Geomorphic Hazard- Landslides: Concept, Types and Causes
59. Geomorphic Hazard- Avalanches: Definition, Types and Factors
60. Integrated Coastal Zone Management: Concept, Objectives, Principles and Issues
61. Watershed: Definition, Delineation and Characteristics
62. Watershed Management: Objective, Practice and Monitoring
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