Mountain building process, internal structure of the earth

Mountain Building Process

The mountain formation refers to the geological processes that involve the building process of the mountains lying on the earth. These processes are associated with the large-scale movement of the tectonics plate of the earth. Thus, the formation of the mountain ranges occurs by means of the movements as opposed to the vertical ones. The plate tectonics, folding, faulting, volcanic activity, igneous intrusion and the metamorphism are all related to the orogenic process of the mountain building. The understanding of the specific landscape features in terms of the underlying tectonic processes is called tectonic geomorphology, and the study of the geologically young or the ongoing process of the mountain formation is known as neotectonics.

Volcanic Mountains

The movement of the tectonic plate creates volcanoes along the plate boundaries which erupt and form the mountains. The volcano arc system is the series of the volcanoes that form near the subduction zone where the crust of the sinking oceanic plate melts.

Most of the volcanoes occur in the band encircling the Pacific Ocean (the Pacific Ring of fire), the Mediterranean across Asia to join the Pacific band in the Indonesian Archipelago. The most important types of the volcanic mountains are the “stratovolcanoes” (Vesuvius, Kilimanjaro and Mount Fuji) and the shield volcanoes (Mauna Loa on Hawaii, a hotspot volcano).

Here. the shield volcano has the gently sloping cone due to the low viscosity of the emitted material mostly basalt. The Mauna Loa is also gently sloped whereas the composite volcano has a more steeply rising cone due to which the emitted materials are more violent and less frequent than the shield volcanoes.

Fold Mountains

When the plates collide and lie one upon other, the plates tend to get fold forming the mountains. Most of the continental mountain ranges are associated with the thrusting or the folding. For example, Jura and the Jagers Mountain.

Block Mountains

The block mountains are formed when the fault mountains are raised or tilted. The higher blocks are known as hosts and the troughs are known as the grabens. When the strong enough tensional forces cause a plate to split apart, it will cause the center block drop down relative to the flanking blocks.

The Sierra Nevada Range, where delamination created the block 650km long and 80km wide that consists of the many individual portions tipped gently west, with east facing slips rising abruptly to produce the highest mountain front in the continental United States.

Internal Structure of the Earth

The internal part of the earth is broadly divided into three parts; the crust, mantle and the core on the basis of the seismic investigation that is separated by the two sharp breaks usually known as the discontinuities.

1. Crust

The crust is the uppermost layer of the earth with the average thickness of 33km. It consists of the verifying layer from (10-40) km in thickness. The lower boundary of the crust is marked as the Mohorovicic discontinuity. The rigidity of the earth increases with the depth of the earth’s crust. It consists of the two layers ; upper sail and the lower sima.

• Sial :

It is also known as the upper continental crust. It consists of all types of the rocks i.e sedimentary, metamorphic, igneous and the granite composition. This layer is rich in silica and alumina. The Conrad discontinuity separates sial and sima.

• Sima :

Sima is also known as the lower continental crust. This layer is rich in silica and magnesium.

2. Mantle

Mantle is the second layer and also the major interior part of the earth which is the source region of most of the earth internal energy. It can be also known as the thick solid zone that surrounds the earth’s core. From the Mohorovicic discontinuity to the depth of 410km, there is a gradual decrease in the seismic velocity which is known as the Gutenberg layer. Here, most of the mantle is on solid rock but under this rigid zone, the last zone called asthenosphere is found. Mantle is also divided into two parts;

Upper Mantle and the lower mantle

• Upper mantle

This is the layer where the rock has less strength and brittleness which break by faulting when unequal stress is too long. Its layer extends from 200-700 km and the temperature lies between 900 to 1600 degree Fahrenheit.

• Lower Mantle

This layer is at the temperature very close to its melting point. It extends from 60-200 km. It is also known as the plastic layer or the soft layer and its temperature are near about the core as 7000-degree Fahrenheit.

3. Core

It is the innermost smooth and the dense portion of the earth where the temperature at the center of the core is 4500 degrees Fahrenheit and density are 135gm/cc. The molten liquid which moves in an electric conductor that generates the earth’s magnetic field. Due to the rotation of the earth, thermal conventional current, the liquid molten part of the earth moves. The inner core has the radius 1255km. The mass and volume of the core is 32% and 16% of the earth respectively. The P-wave velocity decreases sharply and S-wave transmit. It extends from the 2900 km to the center of the earth. It consists of the three parts: Outer core, Middle core and the Inner core.

Earth Materials and the Processes

The rocks present on the earth are igneous, sedimentary and the metamorphic rocks. These rocks and the soil are the common earth materials. The processes which help in the development of the earth surface are termed as the earth processes. The processes are mainly due to the interactions of the internal forces, living creature and the geological agents like wind, water etc. The earth processes play the dominant role as constructive and destructive nature in shaping the earth’s structure.

Types of the Earth’s Processes

Endogenous Processes

The processes which originate with the earth’s crust are the endogenous or hypogene processes. The forces responsible for the endogenous process originate at such processes are the earthquake, volcanism, tectonism, and metamorphism. The features produced by these processes are modified by exogenous processes.

Earthquake

It is the form of energy of the wave motion transmitted through the surface layer of the earth ranging from the faint tremor to the wild motion capable of shaking buildings and causing fissures to open up in the ground. The earthquakes mostly occur due to the underground dislocation of the rock.

Tectonic movement (Diastrophism)

In the course of the geological history of the earth’s formation, the earth’s crust have been crumpled into the fold, lying over one another and broken up into mountains, ridges, ocean, troughs and the other land forms. The tectonic process is of the two types: orogeny (the mountain building process) and epiorogeny (the regional upliftment of the landforms without any deformation).

Metamorphism

The metamorphism process involves the transformation of the pre-existing rocks into the new types of rocks through the action of the temperature, pressure and chemically active fluids obtained through chemical reactions. The special feature of the metamorphic process is that the changes are isochemical and the process takes place in the solid phase.

Volcanism

It is the phenomenon in which the matter is transformed from the interior part of the earth and erupted onto the surface. The rocks and the materials under the earth’s surface reach the surface of the mountain. Hence, the process of the effusion of the magnetic material on the surface of the earth thus forming various structure is known as volcanism.

References

Keller, E.A. Environmental Geology. Columbus, Ohio: Charles E. Miller Publishing Company, Bell and Howell Company, 1985.

Mahapatra, G.B. Textbook of Physical Geology. Shahadra,Delhi-110032: CBS Publishers and Distributers Pvt.Ltd., 1992.