Why Are There No Volcanoes in South Asia?

Why are earthquakes prevalent in south Asia, but almost no volcanoes?

18 earthquakes have hit Delhi NCR (National Capital Region) of India in the three months preceding today (9th of July, 2020). Few more have hit the states of Gujarat in the west and Mizoram in the east in the same duration, in addition to the two Cyclones which struck India and Bangladesh.

Over the millenniums, the Indian subcontinent has witnessed a whole barrage of natural disasters except one- volcanic eruption. It is not a mere coincidence that the subcontinent, despite being categorically rich and diverse in the physiography, from the frosty Himalayas in the north to lush green Nilgiris in the south, there is absolutely no volcanic activity. except for Barren Island in the Andamans, India.

South Asia is defined as the geographical area encompassing Afghanistan, Bangladesh, Bhutan, India, Maldives, Nepal, Pakistan, and Sri Lanka.

The union territory of Ladakh is the frontier of Indian Himalayas in the north and boasts of the highest motorable road in the world | ‘Leh’ ~ Image by Anuj Bansal on Unsplash

Are we floating over magma?

We need to understand a bit of geography to understand the reason behind the frequent earthquakes but the absolute absence of volcanism in south Asia. The earth can be portrayed as a thin crust floating over a solid mantle, which encapsulates a core of iron and nickel. As per the most widely accepted theory of Plate Tectonics, the present-day continental landmasses, as well as the oceans, are in fact ‘plates’ (portions of crust) floating over asthenosphere (the molten part of the upper mantle which contains the ‘magma chamber’). These plates are either converging towards or diverging from or sliding past each other. The plates can either be Continental or Oceanic, depending on the feature above the crust. For instance, the largest ocean of the world is situated over an oceanic plate- the Pacific plate. Present-day South Asia, including India, is a part of the continental Indo- Australian plate.

However, the physical geography of the world was quite different 225 million years ago, when India was a large landmass (synonymous with the present-day peninsular area of India), floating off the Australian coast, separated from the Eurasian mainland by a body of water- ‘Tethys Sea’. About 200 million years ago, the landmass started its 6,000-kilometre journey northward, towards a major plate- the Eurasian plate. About 40 million years ago, the denser Indian landmass collided with and plunged below the Eurasian plate, and the resultant compression, metamorphosis and folding of sediments led to the formation of the Himalayas.

The Himalayas are one of the youngest mountain ranges of the world and bearer of the highest point on earth ~ Mount Everest | Image by Martin Jernberg on Unsplash

The Indian and Eurasian plates are still converging at the rate of about 5 cm every year and consequently, the Himalayas are still rising by a few cm every year as evidenced from satellite mounted high precision atomic clocks and desiccation of lakes in Tibet. Desiccation: Whenever a region is uplifted, the lakes in the region lose water and level of granular terrace changes.

The Ring of Fire

Across the world, almost all the earthquakes and volcanoes are located in the zones where an oceanic and a continental plate collide and converge. In such an event, the denser oceanic plate subducts by 5 to 30 kilometres below the lighter continental plate and the ‘magma’ makes it’s way above through the weak subduction zone formed. For illustration, the Pacific plate upon converging with the North American plate in the east and Eurasian plate in the west, forms a 40,000 km long horseshoe-shaped ring around the Pacific- the Ring of Fire, which houses 75% of the world’s volcanoes and 90% of the earthquakes.

The regions marked in red constitute the Pacific Ring of Fire, which houses the most violent, large and active Volcanoes and Earthquake sensitive zones of the Earth | Illustration by Digitally Learn

The classic case of Himalayan convergence

In case of formation of present-day South Asia, the collision involved two continental plates and not an oceanic plate. In such cases, due to folding and faulting, even those seismic activity is retained which leads to frequent earthquakes but the zone of subduction is as deep as 50 to 70 kilometres. The magma from the asthenosphere cannot penetrate such a thick continental crust and hence it stays in the crust, as a result of which there are no volcanoes in India and the entire of South Asia.

Mt. Fujiyama, located on the Ring of Fire, is the highest mountain of Japan and one of the highest active volcanoes in the world | Image by Leon He on Unsplash

“By discovering nature, you discover yourself”~ Maxime Lagacé