Question

Describe the formation of mountains and their types.

Answer 1

Mountains are classified into three main types depending on the forces that have formed them. Three main types of mountains are

1. Fold Mountains : Fold mountains are the result of large-scale earth movements caused by stresses in the earth’s crust. Such stresses may be caused by weight of the overlying rocks, movements in the mantle, the expansion or contraction of some part of the earth, etc. These stresses subject the rocks to compressive forces, producing wrinkling or folding along the lines of weakness. This is shown in fig. The raising of folds makes the fold mountains.
   
2. Residual Mountains : Mountains which are subjected to weathering and erosion for a longtime, are lowered down and called residual or relict mountains.
   Denudation and erosion by natural agents like winds, water, snow etc., cause the mountains to be lowered but some resistant areas may remain and form residual mountains.
   They may also be formed on plateaus that are dissected by rivers. For example the hills and valleys in the Deccan plateau.
   Some examples of Residual mountains are Nilgiri, Parasnath and Rajmahal Hills in India and the Catskill range in the USA.
   
3. Block Mountains : Horst or a block mountain is an uplifted land mass situated between two adjacent faults. The central block is upthrown or land on the outer-sides of the faults is downthrown so that the central mass appears like a highland. Its surface is like a plateau, but it has steep edges. The Vosges mountains to the west of the Rhine Rift Valley and the Black Forest mountain to the east of the Rhine Rift Valley are good examples of Horsts.