Tectonic theory - solution to one big puzzle(2)

Tectonic plate theory explains reasons for the formation of mountains, eruption of volcanoes and occurrence of earthquakes. It explains the evolution of the layers of the earth as well. This theory was formulated in the 1960s.

It is important to know about the layers of the earth to understand this theory.

Picture: Google images

The earth’s layers are divided into three based on their chemical composition.

1. Crust
2. Mantle
3. Core

Based on the physical / mechanical composition, it is divided into 5.

1. Lithosphere
2. Asthenosphere
3. Mesosphere
4. Outer core
5. Inner core

Lithosphere is the layer of the earth we live. It consists of crust and the outer mantle. It rests on and slides over a layer of partially molten rock known as the Asthenosphere.

According to this theory, Lithosphere can be divided into 7 very large ocean and continental sized plates, 6 or 7 medium sized regional plates and many smaller ones. These plates are constantly moving relative to each other with a speed of 5 - 10 cm per year.

These plates interact along the boundaries. Boundaries are divided into 3 types based on their movement relative to one another.

1. Convergent boundaries: Formed when 2 plates move towards one another.
2. Transform boundaries: Formed when 2 plates slide past one another.
3. Divergent boundaries: Formed when 2 boundaries move away from one another.

Earthquakes, volcanoes and mountains are a result of the movement of tectonic plates along the boundary.

Volcanic eruption

The collision of convergent boundaries results in the formation of subduction zones. Subduction is a process in which the lighter crust moves under the heavier crust and is forced by gravity into the mantle. As the plate reaches deeper into the mantle, an increase in pressure along with an increased temperature causes the crust to melt forming magma. The magma erupts out of the surface to form volcanoes. Ring of fire in the Pacific Ocean is one such example.

Mountain formation (Google image)

Mountains are formed by the interaction of convergent boundaries. At the boundaries the rocks are lifted up and folded to form mountains. Example: Himalayas.

Sea floor spreading (Google image)

At divergent boundaries, tectonic plates move apart. When oceanic plates move apart, it results in seafloor spreading wherein a crack appears on the ocean floor. Hot magma oozes out of the mantle and fills in the crack forming mid-ocean ridges. Magma also spreads out forming new ocean floors and oceanic crust.

Rift valley (Google image)

Drifting of continental plates lead to the formation of valley-like rifts. As the crust widens valleys and volcanoes are formed. Early in the rift formation, streams and rivers flow into the low valley forming lakes. Continual widening of the crust along the boundary resulting in its thinning may lead to breaking off of a piece of the continent forming a new tectonic plate. Water from the surrounding oceans rush in to form new sea basin in the rift zone.

The movement of tectonic plates along the transform boundary results in a crack or fracture called fault on the earth’s crust. The movement of tectonic plates along this boundary can be viewed as a latch-unlatch process. As the plates grind past each other, jagged edges hold on to each other(latch). The release of jagged edges(unlatch) due to plate motion results in earthquakes.

References: https://www.learner.org/interactives/dynamicearth/otherboundaries/

https://www.britannica.com/science/plate-tectonics/Plate-tectonics-and-the-geologic-past#ref261588