Tectonism is the twisting, bending and breaking of the earth’s crust.

1. Tensional Forces

These are forces that cause stress on rocks and stretch the rocks apart.

1. Compressional Forces

These are forces that twist and bend rocks of the earth’s crust.

Tensional and Compressional forces cause folding and faulting of rocks of the earth’s crust.

A FAULT

A fault is made up of an up throw, which is the back that moves upward. The block that moves downward is called a down throw. The surface movement between the up throw and the down throw is called a fault plane.

TYPES OF FAULTS

Faults can be classified according to the way in which the rocks are displaced. There are three (3) main types of faults. These are:

• Normal fault
• Reversed fault
• Tear fault

1. Normal Fault

A normal fault is one in which the rock layer on one side of the fault moves downward and away from the up throw. This is due to tensional forces.

2. Reversed Fault

A reversed fault is one in which, the rocks of the up throw are pushed over those of the down throw. This is caused by Compressional forces at convergent plate margins.

3. Tear Fault

This is a type of fault in which, the fault is vertical, but the rock blocks move horizontally in opposite directions. This occurs when two plates by-pass each other.

Major Landforms of Faulting

Major features produced from faulting include

• Fault scarps also called Escarpments
• Horst (block mountains)
• Rift valleys

1. Escarpments (Fault Scarps)

An escarpment is a step rock wall that separates upland from lowland. It is formed when one rock blocks moves downward or upward creating lowland besides upland. It is also called a fault scarp. Example is the escarpment separating the Adamawa plateau and the Benue lowlands.

2. A Horst (Block Mountains)

A horst is an upland area with faults on both sides. It is also called a block mountain. It is formed either by tension or compression. A horst is formed when the outer blocks of the fault goes down and leaves the middle block standing. It can also be formed when the middle block is uplifted above the level of the outer block. The middle block is called a horst or a block mountain.

3. A Rift Valley

A rift valley is a narrow depression with steep sides and a flat floor. It extends over a long distance. It is formed when some of the middle blocks are forced downwards. The blocks at the sides remain at the same level or they are rained. Examples include:

19. East African Rift valley
19. Mbere Rift valley in Adamawa and
19. Tombel grabs in the South West.

1. Folding

Folding is twisting and bending of rocks along lines of weakness. It is usually caused by compressional forces.

1. Faulting

Faulting is the fracturing of rocks of the earth’s crust. It is caused by tensional forces.

1. FOLDING

This is the bending of rocks of the earth’s crust. This bending is called a fold. It is caused by lateral forces of compression. A fold is made up of an up fold which is the part that bends upward. The part that goes down is called a down fold or a syncline. The sides of a fold are called limbs.                                                                                                                                                                                                                

TYPES OF FOLDS

There are different types of folds. These folds are:

• Simple fold or Symmetrical fold
• Asymmetrical fold or over fold
• Recumbent fold
• Over thrust fold or Nappe

1. Simple fold or Symmetrical fold

In a simple fold the limbs are gentle and are at the same angle. This is because, Compressional forces are equal.

1. Asymmetrical fold or over fold

In this type of fold, one limb is steeper than the other. This is because the force of compression is greater on one side than the other. The fold develop into an over fold.

1. Recumbent fold

Here, one limb lies horizontally over the other due to continuous Compressional forces on the over fold.

1. Over thrust fold or Nappe

In this type of fold, the forces of Compression are very strong on one side. The limb fractures along a fault and the rocks on the unfold slices over the down fold. This up fold is called a Nappe.

MAJOR FEATURES OF FOLDING

Fold Mountain

Fold Mountains are ranged of folded sedimentary rocks which may be as high as 1300m. They are formed by Compressional forces. When two tectonic plates move towards each other, these plates could be an oceanic or continental plates meeting each other. Examples are the Andes, Himalalayes and Rocky mountains.

Stages in the Formation of Fold Mountains

• When two plates meet, for example an oceanic plate and a continental plate, the heavier oceanic plate goes under the lighter continental plate.
• Sedimentary beds in between the two plates begin to fold due to the force of compression.
• An force of compression continuous the sedimentary rocks are highly uplifted forming fold mountains.

1. FAULTING

Faulting is the fracturing of the earth’s crust and the displacement of the rock layers on both sides of the fracture.

A fracture on a fault is a break in the earth crust. Faulting is caused by either tensional or Compressional forces.