Unravelling secrets of Deccan Trap

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How were the Western Ghats formed? And how are they related to Deccan Trap?

The Western Ghats, spanning a distance of nearly 1,500 km from Gujarat to Kerala, is one of the most dominant land forms of the Indian subcontinent. While their northern cousins, the Himalayas, may be more famous, the Western Ghats have an equally impressive story behind it.

So, do you know how the Western Ghats were formed and what their connection with the Deccan Trap is?

Way back in time…

For us to trace the origin of the Western Ghats we need to go back in time. In fact, way back to the time of the supercontinent Pangaea. The Greek word ‘Pangaea’ means ‘All the Earth’. All the continents as we know it today were fused together into one super big land mass. The southern portion of this super continent was called Gondwanaland. Gondwanaland is also known as Gondwana.

About 150 million years ago, Gondwana started breaking up into pieces. Keep in mind that we are talking about geology here, so the split was not a one day affair. This was something that would happen over millions of years, with the Earth’s plates moving at the incredible speed of 6cm a year.

Do you know what made up Gondwana? Gondwana included present day Africa, South America, Antarctica, Australia and India.

India begins its long journey North

The great Indian poet, Rabindranath Tagore, had penned the immortal lines of “Ekla Chalo re…”. Translated from Bengali, this literally means ‘Walk Alone’. India’s destiny from time immemorial has been to pave its own path and we seem to have picked up this trait when the Indian subcontinent broke away from Gondwana!

India’s slow drift away from Gondwana would find it parting way with Antarctica and Australia, and later with Madagascar and Seychelles. This journey would end with India crashing head-on to the Eurasian plate and pushing up the Tibetan plateau and the mighty Himalayas.

Did you know…
While we are at it, let this sink in properly – India and Antarctica were neighbors at one point. A 150 million years ago, both India and Antarctica were in the Southern Hemisphere. The Antarctic landmass was covered with vegetation instead of ice as it is today. And while dinosaurs would have moved across the landmasses, there surely weren’t any penguins hopping between India and Antarctica!

Geology behind mountains

Before we get to the formation of the Western Ghats, let us take a look at some of the common ways a mountain range is formed.

Cause	Description
Fault lines	Stress generated due to plate movement causes mountains to rise. Plates could collide with each other and the pressure generated at the collision zone leads to mountain formation. One of the plates can possibly go under and lift the other plate. Or alternatively parts of both plates could be forced up, especially if both plates have similar type of rock. E.g. Himalayas Mountains can also be formed when plates move apart from each other.
Volcanic Activity	Volcanic activities at the boundaries of the plates or around volcanic hotspots cause volcanic eruptions. These eruptions spew out rock from deep within Earth and lead to mountain formation. E.g. Mount Kilimanjaro. Such mountains are easily identified by their cones. Intense heat from hotspots under the plates can cause arching of the Earth’s crust. E.g. Western Ghats

Did you know…
A geological hotspot is an area of volcanic activity where the magma under the Earth’s crust is significantly hotter than the surrounding areas. Magma from these hotspots slowly flow up due to convection. This plume of magma from deep within Earth flowing up to the mantle is called a Mantle plume.

Watch this video to get a glimpse of mantle plume formation

Reunion after the breakup

Once India broke off from Gondwana, we were an island floating off in the Tethys sea. Giving us company in this northward journey were Madagascar and Seychelles. About 80 million years ago, Madagascar separated off India. Seychelles split off around 65 million years ago, leaving India to drift off alone in a north-easterly direction.

Did you know…
Once Madagascar separated from India, the flora and fauna on Madagascar remained trapped there forever. There was no land bridge from Madagascar to either the Indian subcontinent or to Africa. The unique lifeforms seen in Madagascar is the result of this isolation. It is estimated that nearly 90% of the life forms seen in Madagascar are unique to the island seen nowhere else in the world.

At around this time, Central India passed over the Reunion Island volcanic hotspot. As the plate moved over the hotspot, the intense heat from under the plate caused the Earth’s crust to bulge up. This arching of the curst is what led to the formation of the Western Ghats. The entire southern part of the Western Ghats are believed to have been formed entirely due to this phenomenon and the rocks here are extremely old, dating to about 2000 million years.

Deccan Trap

The Reunion hotspot was still not done with the Indian plate! What was to follow was at an even more epic scale – the formation of the Deccan Trap.

As the mantle plume from the hotspot rose up and came into contact with the crust, it spread out under the crust over a very large area. Since this magma is mostly Basalt rock, geologists call it ‘Basalt Magma’. The magma erupted out on to the surface through fissures flooding an area close to 1.5 million sq.km.. We call this magma flow as the Deccan trap.

Did you know…
Geologists use the term ‘Continental Flood Basalt’ for flooding of basalt magma at a ‘continental’ scale. Another term is ‘Large Igneous Provinces’. Whatever term you choose to use, we are talking about a serious amount of magma gushing out from the depths and spreading over an enormous area.

So what’s so deadly about mantle plumes and flood basalts – the volcanic eruptions and magma flow lasts for MILLIONS of years. Compared to this, the typical volcanic eruption that we are used to seeing on TV lasts for just a few days or weeks, that too sporadically. The Deccan Trap is thought to have been partly responsible for the extinction of the dinosaurs.

With a thick layer of basalt on the Deccan plateau, the entire region was at an elevation compared to its surroundings. Over time, rain and rivers carved their way through the edges of the plateau, leaving behind deep canyons and gorges and mountain chains. This is the northern part of the Western Ghats as we know it today.

How far have we travelled

You can see how far we have drifted away from the Reunion hotspot. The Reunion hotspot is so called because it is (currently) under the Reunion Islands. The red zone over India is the Deccan Trap, map representation only indicative and not to scale.

Effect of Erosion

The current form of the Western Ghats has been impacted significantly by erosion. The western slopes of the mountain are steep, the rivers originating here are fast flowing owing to the steep slopes. Waterfalls are abundant along these rivers, Jog falls in Karnataka being a good example. These rivers drain into the Arabian Sea, but no deltas are formed since there is not enough land to form one.

Western Ghats are the ‘Great Escarpment of India’

The eastern slopes are more gradual, rivers originating here are slow flowing. There are very few waterfalls along this route, and these rivers punch through the lower altitude Eastern Ghats before draining into the Bay of Bengal in deltas.

Did you know…
How thick is the basalt layer in the Deccan Trap? Quite thick actually, in many places up to 2km thick. How high is 2km – 2km is more than 2 times the height of Burj Khalifa, the tallest building in the world! You can now ponder how much of lava would have flown out to create such a thick layer over a million sq.km..

Great Escarpment

The Western Ghat is known as the great ‘Escarpment of India’. Escarpment means steep slope. The northern part of the Ghats, being the edge of the elevated Deccan plateau, has a cliff like edge on its western side.

South-East bias

Do you know that the Indian plate is actually tilted to the East? As the crust arched up on the west coast, the Indian plate tilted eastward. That is the reason why most of the peninsular rivers flow eastward and drain into the Bay of Bengal. Examples include Krishna, Godavari and Kaveri.

Not just that, the Deccan plateau is tilted southward too! Geologists believe that this is because of the nature of the rock in the southern Western Ghats. The rocks found in the southern ranges are older and heavier than the ones in the northern part and this causes the tilt.

Palakkad to Madagascar

If you thought that the geological history of the Western Ghats was baffling, wait, there is more to come! Cutting through the Western Ghats is a 30km wide opening in the mountain – the Palakkad Gap in Kerala. This gap has the Nilgiri range on one side and the Anamalai range on the other.

So what’s special about this gap? Geologists believe that the Palakkad Gap is where, hold your breath, India and Madagascar split away. Remember that Madagascar was with India while we were travelling northward. When passing over the Marion hotspot, the plates split and drifted apart. As per this article in the Geological Society of India, the Ranotsara Gap in Madagascar apparently fits exactly into the Palakkad Gap giving geologists a vital clue about their connection! ‘Blistering Barnacles’ as Captain Haddock would have said!mana

Predating the Himalayas

The formation of the Western Ghats and the Deccan Trap had all completed much before the Indian landmass had crashed into Eurasia and formed the Himalayas. Geologically the Western Ghats are much older than the Himalayas.

Want to know how the Himalayas were formed – read an earlier post on that topic here

Summing it up

The entire Western Ghats from Gujarat to the southern tip of India is clearly visible in this NASA photograph. Can you make out the key geological features here?

• The northern Western Ghats (Gujarat through Maharashtra up to Goa) hugs the Arabian Sea. This is the great escarpment of India.
• Central and southern Western Ghats are further inland from the sea shore. This is the area of the Konkan and Malabar coast. Erosion and sedimentation are considered a primary cause of this.
• You can also make out that the Deccan plateau is bounded on the West by the Ghats. It is believed that with erosion and breaking of rocks along natural fault lines, the Ghats have moved eastwards to where we see them now.
• The Palakkad Gap splits the southern part of the Western Ghats, you can make it out as a V-shape protruding away from the mountains.

Postscript

Geologists are constantly learning more about continental drift and continent formation. The last word on this topic has not yet been spoken. We can only hope that their studies will help shed more light in this intriguing field.

Did you know…
The formation of the Eastern Ghats has an equally, if not more, interesting story behind it. We will discuss that another time, but if you are curious take a look again at this picture to see what was on India’s east coast when we split from Gondwanaland. Did that piece of land influence the formation of the Eastern Ghat?

Further Reading & Viewing

While Geology tends to sound a bit baffling initially due to the complex terms involved, there are quite a few good videos explaining the basic concepts.

Geologist Dr.Suvrat Kher has a very good video on the lava flow that created the Deccan Trap, I would highly recommend you watch this video.

A very detailed and thorough blog on the formation of the Western Ghats can be found here.

Ever heard of Shiva impact crater and the theory behind this crater and the extinction of the Dinosaurs – read more about that here and here.

Food for thought

So what do you think about the whole Western Ghat formation story? Do you think geology is more than collecting rock samples, maybe a great career option? Share your thoughts in the Comments section below.