Last class revision (5:14 PM)

Earth's movement (5:30 PM)

• Various forces from the earth's interior as well as outside the earth's surface cause physical stress and chemical actions on the earth's material bringing about changes in the configuration of the surface of the earth called a geomorphic process.
• The geomorphic process results from two types of forces, endogenetic and exogenetic.
• Endogenetic forces:
• These are the forces acting from the earth's interior, the source of energy is radioactivity and primordial heat.
• They result in large-scale upliftment or subsidence or folding and faulting.
• They are responsible for the formation of major structural units of the earth's surface.
• Exogenetic forces:
• These are the forces acting on the earth's surface from above the surface.
• The sources of energy are sunlight and gravity.
• Wind, water, and glaciers are the different agents of exogenetic movements.
• These forces result in minor topographical features such as valleys and caves. 

Endogentic movements (6:11 PM)

• They are classified into dystrophic and catastrophic movements.
• Catastrophic movements (Sudden movements):
• These are unpredictable movements of shorter duration.
• These movements can be observed.
• Examples are earthquakes, volcanic eruptions, etc.
• Diastrophic movements:
• Some movements move, elevate, and buildup up the portions of the earth's crust.
• These movements operate very slowly and led to the formation of primary landforms.
• They are of 3 types: tectonic, isostatic, and eustatic.
• Tectonic movement:
• The Word tectonic means to build.
• These are continent and mountain-building movements affecting the earth's surface.
• They are of 2 types Epirogenic and orogenic.
• Epirogenic movements:
• These are vertical movements caused by radial forces.
• These are characterized by large-scale upliftment/ emergency and subsidence/submergence of land areas.
• They are very slow and widespread.
• These movements led to the continental building.
• An example is the gradual upliftment of the Deccan plateau and the slow subsidence of the northern coast of the Gulf of Mexico.
• Orogenic movement:
• These are mountain-building movements caused by tangential forces.
• They involve intense folding and faulting of narrow belts.
• The tangential forces are of 2 types, Compressional resulting in folding, and tensional resulting in faulting.
• Folding:
• When the compressional forces the earth's rocks to push or squeeze against each other.
• It results in the formation of folds 
• Folds are structures in which the layers are bent or distorted without the loss of continuity.
• Faulting is when tensional forces pull the rocks apart, it results in the formation of faults.
• Faults are the fractures, through which primary surfaces are broken and displaced, with the loss of continuity.
• Type of faults:
• The up-folds are called anticlines and the Downfolds are called synclines.
• A fold will have two sides called limbs.
• Symmetrical Fold:
• If the limbs of a fold are inclined at the same angle, it is called a Symmetrical fold.
• Asymmetric Fold:
• If one of the limbs is inclined more than the other, it is called an Asymmetrical fold.
• Overfold:
• It is a fold where the strata in one limb have been folded beyond the vertical axis.
• Recumbent Fold:
  It is a fold lying down resulting from the continuation of pressure on one of the limbs. 
• Nappe:
• It is formed when the pressure exerted upon a Recumbent Fold is sufficiently great to cause it to be torn from its roots and thrust forward. 
• Nappes are well-developed in the Himalayas.
• Types of Faults:
• Normal Fault:
• When one of the blocks moves downward relative to the other due to tensional forces it is called a Normal fault or Dip Slip Fault.
• Reverse Fault: 
• When one block moves up about the other one due to compressional forces it is called a Reverse Fault or Thrust Fault.
• Strike-Slip Fault:
• Where both the blocks move across each other involving no vertical movements it is called  Strike-slip or Transform Fault.
• In a fault, the upthrust block is called a Horst and the down-dropped block is called a Graben.

The difference between the fold and the fault mountains(8.03 PM):

• Fold mountains:	Fault/block mountains:
  It is because of the folding process.	Due to the Faulting process
  Only compressional force	Both compressional and tension force
  They are greater in  length	They are greater in width.
  For example Himalayas and Alps	For example Vindhyas and Blackforest

The topic for the next class: Isostatic movement and Eustatic movement.