World Geography Part 8 – Types of Fault

Important Geographical Phenomenon

  1. As we know that there are several factors behind folded structure, in the same way tensional and compressional forces causes displacement of rock along a plane.
  2. The force may be vertical or horizontal and sometime it may be in both ways.
  3. These crustal fractures depend on the strength of rock and intensity of tensional force.
  4. Fractures are divided into two parts
    • Faults
    • Joints

Faults

  1. A fault is a fracture is a fracture in the crustal rocks, due to tensional movement caused by the endogenetic forces, wherein the rocks are displaced along a plane, known as fault plane.
  2. The movement responsible for the formation of a fault may operate in vertical or horizontal or any direction.

Types of fault

fault-types

Normal fault

  1. These are formed due to displacement of both the rocks blocks in opposite directions,
  2. Due to fracture consequent upon greatest stress, the fault plane is usually between 45 degree and the vertical.

Reverse faults

  1. These are formed due to the movement of both the fractured rock blocks towards each other.
  2. The fault plane, in a reverse direction is usually inclined at an angle between 40 degree and the horizontal (0degree).

Lateral or strike faults

  1. These are formed when the rocks blocks are displaced horizontally along the fault plane due to horizontal movement.
  2. When displacement of rock occurs to the left, they are called left – lateral or sinistral fault.
  3. When displacement of rock occur to the right , they are called right – lateral fault or dextral fault.

 

Step faults

  1. When a series of faults occur in any area in such a way, that the slopes of all the fault planes of all the faults are in same direction.

Exogenetic forces

  • The Exogenetic forces or processes also called denudational processes or destructional
  • They are continuously engaged in the destruction of the relief features created by the endogenetic forces.
  • The exogenic processes derive their energy from atmosphere determined by the ultimate energy from the sun and also the gradients created by tectonic factors.
  • Gravitational force acts upon all earth materials having a sloping surface and tend to produce movement of matter in down slope direction.
  • Force applied per unit area is called stress.
  • Stress is produced in a solid by pushing or pulling. This induces deformation.
  • Forces acting along the faces of earth materials are shear stresses (separating forces).
  • It is this stress that breaks rocks and other earth materials.
  • The shear stresses result in angular displacement or slippage.
  • The gravitational stress earth materials become subjected to molecular stresses
  • Molecular stresses may be caused by a number of factors amongst which temperature changes, crystallisation and melting are the most common
  • Chemical processes normally lead to loosening of bonds between grains, dissolving of soluble minerals or cementing materials
  • The basic reason that leads to weathering, mass movements, erosion and deposition is development of stresses in the body of the earth materials.
  • As there are different climatic regions on the earth’s surface the exogenic geomorphic processes vary from region to region.
  • Temperature and precipitation are the two important climatic elements that control various processes
  • All the exogenic geomorphic processes are covered under a general term, denudation
  • The word ‘denude’ means to strip off or to uncover. Weathering, mass wasting/movements, erosion and transportation are included in denudation.
  • Within different climatic regions there may be local variations of the effects of different climatic elements.
  • Due to altitudinal differences, aspect variations and the variation in the amount of insolation (amount of sun rays) received by north and south facing slopes as compared to east and west facing slopes.
  • Differences in wind velocities and directions, amount and kind of precipitation, its intensity, the relation between precipitation and evaporation, daily range of temperature, freezing and thawing frequency, depth of frost penetration, the geomorphic processes vary within any climatic region.
  • Climatic factors being equal, the intensity of action of exogenic geomorphic processes depends upon type and structure of rocks.
  • The term structure includes such aspects of rocks as folds, faults, orientation and inclination of beds.
  • Presence or absence of joints, bedding planes, hardness or softness of constituent minerals, chemical susceptibility of mineral constituents.
  • Different types of rocks with differences in their structure offer varying resistances to various geomorphic processes
  • Under varying climatic conditions, particular rocks may exhibit different degrees of resistance to geomorphic processes and hence they operate at differential rates.
  • The effects of most of the exogenic geomorphic processes are small and slow and may be imperceptible in a short time span.

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