Himalayas are one of the loftiest and rugged mountain systems of the world. Along the Northern borders of India, they stretch in west-east direction from Indus to Brahmaputra.

• 225 million years ago (Mya) India was a large island situated off the Australian coast in a vast ocean. It was separated from Asia by the Tethys Sea. India started a northward drift towards Asia due to tectonic plate movement at the time when super-continent Pangea began to break up about 200 Mya.
• 80 Mya India was 6,400 km south of the Asian continent but moving towards it at a rate of between 9 and 16 cm per year. At this time Tethys Sea floor would have been subducting northwards beneath Asia and the plate margin would have been a Convergent oceanic-continental one just like the Andes today.
• Most of the thick sediments on the Indian margin of the ocean were scraped off and accreted onto the Eurasian continent in what is known as an accretionary wedge. These scraped-off sediments are what now form the Himalayan mountain range.
• From about 50-40 Mya the rate of northward drift of the Indian continental plate slowed to around 4-6 cm per year. This slowdown is interpreted to mark the beginning of the collision between the Eurasian and Indian continental plates, the closing of the former Tethys Sea, and the initiation of Himalayan uplift.
• The Eurasian plate was partly crumpled and buckled up above the Indian plate but due to their low density/high buoyancy neither continental plate could be subducted. This caused the continental crust to thicken due to folding and faulting by compressional forces pushing up the Himalaya and the Tibetan Plateau. The thickening of the continental crust marked the end of volcanic activity in the region as any magma moving upwards would solidify before it could reach the surface.
• It is important to note that the Himalayas do not comprise a single range but a series of at three ranges running more or less parallel to one another. They are supposed to have emerged in three different phases following one after the other. After the Great Himalayas were formed, the second phase took place about 25-30 Mya when the Middle Himalayas were formed. The Shiwaliks were formed in the last phase of the Himalayan orogeny.
• The Himalayas are still rising by more than 1 cm per year as India continues to move northwards into Asia, which explains the occurrence of shallow focus earthquakes in the region today. However, the forces of weathering and erosion are lowering the Himalayas at about the same rate. This shows that Himalayas are still in the process of formation. That's why Himalayas are considered young and restless.