Question – Explaining in detail the origin of Himalayas, explain why it is often called young and turbulent mountains. – 29 November 2021
Answer – The Earth’s surface, the lithosphere, is made up of small continental plates. It constantly rests on a partially molten rocky layer, the asthenosphere, and keeps sliding over it. Its special feature is that there is a lot of pressure on its edges, and this is the place where natural accidents like earthquakes and volcanic eruptions keep happening. At the sites where two plates collide, such a pressure is created that it causes huge folds on the surface, from which high mountain ranges are formed.
Origin of Himalayas – The Himalaya Mountains are one of the highest and most inaccessible mountain systems in the world. Along the northern borders of India, these mountain ranges extend in a west-east direction from the Indus to the Brahmaputra. 225 million years ago, India was a vast island, located off the Australian coast in a vast ocean. The Tethys Sea separated it from Asia. Later, about 200 million years ago, when the great continent Pangea started disintegrating, due to tectonic plate movement, India began to move northwards towards Asia.
About 80 million years ago, India was located 6,400 km south of the Asian continent, but it was moving towards it at the rate of 9-16 cm per year. At the same time, the bottom of the Tethys Sea began to subduct northward under the continent of Asia, and this plate boundary became an oceanic-continental convergent boundary similar to the present-day Andes mountain range.
Later, a thick layer of sediment at the Indian boundary of the sea was displaced and deposited on the Eurasian continent, known as an accretionary wedge. The effect of compressive forces on this deposited depression has led to the formation of the present Himalayan mountain range.
About 40–50 million years ago, the rate of northward displacement of the Indian continental plate slowed to 4–6 cm per year. This slow movement has been explained as the beginning of the collision between the Eurasian and Indian continental plates, the filling of the eastern Tethys Sea, and the beginning of the uplift of the Himalayas.
The Eurasian plate partially folded over the Indian plate, but due to the low density/high buoyancy, neither continental plate could be subducted. This led to the uplift of the Himalayas and the Tibetan Plateau by increasing the thickness of the continental crust as a result of folding and faulting due to compressive forces. The thickening of the continental crust marked the end of volcanic activity in this region, as vertically moving magma solidifies before reaching the surface.
However it is important to note that the Himalayas did not form as a single mountain range, but evolved into three mountain ranges spread almost parallel. They are believed to have emerged in three distinct phases, one after the other. After the formation of the Great Himalayas, in the second phase, about 25-30 million years ago, the Central Himalayas were formed. Shivalik was formed in the last phase of Himalayan mountain formation.
The Himalayas are currently rising at a rate of more than 1 cm per year as the Indian peninsula continues to move north, which explains the shallow epicenter earthquakes currently in the region. However, the process of erosion of the Himalayas by weathering and erosional forces is also taking place at almost the same rate. It is clear from this that the Himalayas are still in the process of formation. This is the reason why the Himalayas are considered young and turbulent.