give reason for each of the following:
1. why asthenosphere though underneath the crust is in a semi molten state.
2. Exogenic forces are also called destructive forces.
3. Residual mountains are also called mountains of denudation.
Answers
Explanation:
(1) Because lava is present below the crust layer.
(2) Exogenic Processes or Denudation
The processes which occur on earth’s surface due to the influence of exogenic forces are called as exogenic processes or exogenic geomorphic processes.
Weathering, mass wasting, erosion, and deposition are the main exogenic processes.
All the exogenic processes are covered under a general term- denudation, which means strip off or uncover.
The elements of nature capable of doing these exogenic processes are termed as geomorphic agents (or exogenic geomorphic agents). E.g. the wind, water, waves etc.
Note: A process is a force applied on earth materials affecting the same. An agent is a mobile medium (like running water, moving ice, winds, waves etc) which removes, transport and deposits earth materials.
Geomorphic processes and geomorphic agents especially exogenic, unless stated separately, are one and the same.
Gravity and gradients are the two things which make these agents mobile.
All the movements either within the earth or on the surface of the earth occur due to gradients– from higher levels to lower levels, from high pressure to low pressure etc.
The exogenic forces derive their energy from atmosphere determined by the ultimate energy from the sun and also the gradient created by tectonic factors. We have already discussed in previous articles that slopes on earth surface are mainly created by tectonic factors or earth movements due to endogenic forces.
We know that force applied per unit area is called as stress. Stress is produced in a solid by pushing or pulling.
The gravitational force acts upon all earth materials having sloping surface and tends to produce movement of matter in the down-slope direction. This creates stress and induces deformation to the particles.
(3) RESIDUAL Mountains Are formed From already existing
mountains which are lowered or reduced by agents of
denudation such as Running water, ice and wind, Residual
mountains are therefore the remains of already existing
mountains. Some hard, and the very resistant parts of the
existing mountains remain after the lowering of the upper
part. This remaining part is called Residual Mountains which
are also Mountains of Denudation. the Aravalli Mountain
and the Parasnath mountain of Bihar belong to this type.