The Himalayas: the home of snow, the cordillera with the Earth’s highest peaks, including the highest Mount Everest, and with ten of the fourteen 8k+ metre peaks. The source of three serene rivers-Ganges, Indus, and the Brahmaputra. The magnanimity of these mountains is beyond words.
Becoming a mountain is not a quick and easy task. Who can say that these supreme, gigantic, deserted and calm mountains were once a deep sea full of vibrant life?
“Great heights come from great depths”.
1. The vibrant sea before the Himalayas:
The earth initiated its visible land with a single supercontinent known as Pangaea, 250 million years ago. The Pangaea went through its bifurcation, with the northern Angaraland and southern Gondwanaland forming a geosyncline-Tethys sea, a long and narrow natural trough. Rivers from both continents submerge themselves in the Tethys with huge sediments. The continents then fragmented into different lands.
2. The Science of tectonics.
Plate tectonics describes that the earth’s lithosphere is broken into several plates floating on the asthenosphere’s ductile magma layer (2nd layer of interior earth). Plates move horizontally over the asthenosphere as hard units. The Simatic oceanic plates are relatively thinner than the sialic continental plates. The movement of these lithospheric plates causes the formation of various landforms and is the principal cause of all earth movements. These crustal plates get pushed by the convection currents in the mantle, and these currents are generated by thermal gradients.
3. Convection currents.
Convection currents are formed due to radioactive elements causing thermal differences in the mantle. Wherever rising branches of these currents meet, oceanic ridges are formed on the seafloor due to the divergence of the lithospheric plates (tectonic plates), and wherever the falling branches meet, trenches are formed due to the convergence of the lithospheric plates (tectonic plates).
4. Convergence of plates.
The edge of convergence of tectonic plates is known as convergent boundaries or destructive boundaries. In such a kind of interaction, two lithospheric plates collide against each other.
The zone of collision may go through crumpling and folding, and folded mountains may erect (orogenic collision). The Himalayan Boundary Fault is one such example. When one of the plates is an oceanic plate, it gets embedded in the lighter asthenosphere of the continental plate, and, as a result, trenches are formed at the zone of subduction. At the convergent edge, a part of the plate is destroyed, hence the name Destructive Edge. The subducted part gets heated up and is thrown out, forming volcanic continental arc systems such as the trans-Himalayas.
5. Movement of Indian plate.
It will be surprising to know that India was a large island a few million years ago. India was a part of southern Gondwanaland which wanted to collide with northern Angaaraland. India started her northward journey towards Eurasia about 200 million years ago when Pangaea broke. The geosynclines of the Tethys Sea separate the Indian plate from the Eurasian plate. The Tibetan block was a part of the Asiatic landmass.
Building of the Himalayas.
Himalaya is nothing but a byproduct of plate collisions. India collided with Asia about 40-50 million years ago. By this time, huge sediments deposit formed in the geosynclines of the Tethys by rivers of both continents. By the time the Indian plate is heading close towards the Asian plate, these deposits start to squeeze and fold. The fact that the summit of Mount Everest is consists of marine limestone strengthens the acceptability of this process.
When this oceanic crust is partly folded and then subducted, the moment of collision of the 2 continental plates comes. These are the Indian plate and the Eurasian plate. Very high mountains are associated with the convergence of two continental plates. In such a convergence, high forces cause compression of the plate margins and hence the sediments from both the plates are squeezed and folded to give rise to the Fold Mountains.
The relatively denser plate slights beneath the lighter plate, uplifting the lighter plate, giving such mountains great heights. The height of the Himalayas is still increasing. As the continental plate can’t subduct deep inside the mantle, it didn’t melt and, therefore, the crust is very thick. Hence, such mountains are volcano freeze zones but can have regular earthquakes. We should be aware of the fact that the Indian plate is still going beneath the Eurasian plate. When the energy surpasses a particular level, it is released, which causes earthquakes. The continent-continental collision gives rise to mountains that are located deep inside the continent, unlike the coastal mountains such as the Andes and Rockies. As the collision is very powerful, earthquakes and landslides are very common in this region.
➢ PHASES OF FORMATION
The Himalayas are made up of at least three ranges that run more or less parallel to one another, rather than a single range. As a result, the Himalayas evolved in three phases after emerging from the Himalayan Geosyncline, i.e. the Tethys Sea.
• The first phase began about 50-40 million years ago when the Great Himalayas were formed. The Great Himalayas have formed roughly 30 million years ago. Mount Everest, K2, Nanga Parbat are part of this.
• The Middle Himalayas have formed about 25 to 30 million years ago, in the second phase.
• The Shiwaliks emerged during the last stages of the Himalayan orogeny, roughly two million to twenty million years ago. Tibetan plateau also holds Some Shiwalik hills’ fossil deposits. It suggests that the climate of the Tibet plateau in the past was comparable to that of the Shiwalik hills.
According to recent studies, the Himalayan region has experienced a crustal shortening of around 500 kilometres due to the convergence of the Indian and Asian plates. The seafloor spreading over the Indian Ocean’s oceanic ridge has compensated for this shortening.
➢ Evidence for the Rise of the Himalayas
• Today’s satellites use high-precision atomic clocks that can measure even a small height of one centimetre with accuracy. The heights of various locations determined by satellites suggest that the Himalayas increase by a few centimetres every year. The current Himalayan height increases at 5-10 cm per year.
• Due to uplift, the lakes in Tibet dry up (lose water) and keep the gravel races much higher than the current water level. This could only be possible in the event of uplift in the region.
- The frequent tectonic activity (occurrence of earthquakes) in the Himalayan area shows that the Indian plate is moving further north and sinking into the Eurasian plate.
- This means that the Himalayas are still rising through compression and have not yet reached isostatic equilibrium.
- Himalayan rivers are in their youthful stages and have rejuvenated recently. This shows that the Himalayan landmass is increasing and the rivers have remained in a youthful state for a long time.
The life of the land.
Life is just a unique moment between birth and death; either it is us, human beings, or the gigantic continents.
A single Pangaea fragmented into several small parts and then the collision between India and Eurasia adjoined the two lands, forming a larger continent.
The theories of geology suggest that there were similar processes of combining and breaking continents even before Pangaea. The continents are joining again and will become a great continent and the process will start afresh.
Tectonics will continue. Mountains will form and erode. But to achieve great heights like the Himalayas, you have to dive into the great depths of Tethys.
For further reading- https://en.wikipedia.org/wiki/Himalayas
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