In a tank filled with glucose syrup and rigged to mimic continental movements, geologist Santanu Bose has unriddled the rise of the Himalaya and identified a pivotal event that would stop its rise.
Bose, who teaches at Calcutta’s Presidency University, and his collaborators in Europe and China have through table-top experiments bolstered the evidence for tectonic mechanisms driving India’s northward slide, a subject of speculation among geologists for years.
Scientists have known for decades that India split from a supercontinent, named Pangea, about 130 million years ago to move northward to eventually collide with Eurasia about 55 million years ago, the continental convergence giving rise to the 2,400km-long Himalaya.
The India-Eurasian convergence has continued since then and proceeds now at about 4cm per year translating into the ongoing rise of the Himalaya — currently measured at an average of about 1cm per year.
“India’s northward travel after the collision has been a puzzle,” Bose, a professor of geology, told The Telegraph. “Conventional plate tectonics theory suggests that a collision between two continental plates should stop the driving force for plate motion. What then is the source of energy for the ongoing India-Eurasia convergence and the rise of the Himalaya? That is the puzzle.”
Two years ago, geologist Andrew Parsons at the University of Oxford and his colleagues used geological tomography to propose that the Indo-Australian oceanic plate is sinking into the Sunda trench, a narrow and deep Indian Ocean region along the Andaman and Nicobar islands that curves eastward along Sumatra and Java. This so-called subduction process is driving India’s northward movement post-collision.
Their analysis indicated that since the onset of the collision, the Indian continental slab had migrated 1,000km northward through the mantle, driven by subduction of the neighbouring Indo-Australian oceanic plate. “Our study shows that the sinking behaviour of one slab can influence that of another slab in the same network,” Parsons and his colleagues said, reporting their work in the Geophysical Research Letters.
Now, Bose and his collaborators have shown that the pulling force generated by the sinking of the Indo-Australian plate along the Sunda trench continues to pull India northward into Eurasia.
Bose designed the experiments at Monash University while on an Australiangovernment research fellowship, working with geologist Wouter Schellart, an expertin the reconstruction of tectonic processes in a laboratory.
They set up an acrylic tank filled with glucose syrup in which they placed viscous silicone slabs that simulated the continental and oceanic plates, while the syrup simulated the Earth’s upper mantle upon which the plates rest.
In their experiments, they initiated subduction by gently pushing a slab representing the oceanic plate into the syrup to mimic the subduction.
They chose materials — glucose syrup and silicone slabs — whose densities with respect to each other would be similar to the densities of the continental and oceanic plates and the upper mantle.
They watched how India behaved with and without subduction. Without the subduction in the Sunda trench, India’s northward movement would have stopped over 30 million years ago, their study has suggested.
“The Sunda trench is the source of the energy that keeps the collision going and explains why the Himalaya continues to rise today,” Bose said.
Their study has suggested that if the Indo-Australian oceanic plate breaks up — fractures — in the future into two plates, India’s northward push into Eurasia would cease and the rise of the mountains would eventually stop.
Last updated on 01 May 2023
