Digging deep to fathom how oceans are formed

I grew up in the coastal state of Kerala and have spent a large part of my life close to the sea. This probably triggered in me a desire to study how ocean basins are formed. Hence, after completing my Masters in Marine Geophysics, I enrolled for a PhD with the IITB-Monash Research Academy. My project is titled, ‘A thermo-mechanical study of the southern Red Sea – Afar triple junction region: implications on the rift evolution’.

The IITB-Monash Research Academy is a collaboration between India and Australia that endeavours to strengthen scientific relationships between the two countries. Graduate research scholars like me study for a dually-badged PhD from both IIT Bombay and Monash University, spending time at both institutions to enrich our research experience.

The earth has a radius of about 6,371 km. Interestingly, the crust — or the uppermost thin layer on which we live — is just 30-70 km thick beneath continents and 5-10 km thick beneath oceans. This thin peel of the earth and its underlying layer (called the upper mantle) — together named as lithosphere — move, evolve, and lead to almost all the significant geological processes on the earth’s surface such as volcanic eruptions and earthquakes. The lithosphere is not a single shell but is broken up into different moving plates. The plates interact with each other along their boundaries, which give rise to formation of mountains like the Himalayas and deep cavities like the Mariana trench (the deepest spot in the world), formation and closure of oceans, etcetera. A place where three such plates meet, called a triple junction, is extremely significant.

Afar — where the African, Arabian, and Somali plates meet — is one such triple junction. The three arms of the Afar triple junction, the East African rift, Red Sea and Gulf of Aden, represent present-day examples of rupturing of the continental lithosphere to form ocean basins.

Oceans are formed — and gradually disappear — on the earth’s surface continuously when such plates move away from and towards each other, respectively. The rupturing of the lithosphere is the first stage of ocean basin formation. As the plates continue to drift apart, small ocean basins form between the newly broken continents, floored by fresh hot rock that is upwelled from below the plate which will eventually cool down. This early stage of ocean formation is called the juvenile stage and the Red Sea is a perfect example of this. The Red Sea, one arm of the Afar triple junction, is being formed because of the drift of Arabian and African plates away from each other.

The Red Sea, being an incipient ocean basin, provides a unique opportunity to understand the process of ocean formation through continental rupture. Also, the southern part of the Red Sea is morphologically and geologically distinct from its northern part, as it is close to the Afar mantle plume near Ethiopia. Afar plume is a large column of hot rock rising from deeper mantle interacting with the base of the lithosphere of the Afar area and forming a large volcanic mass over the surface. I am using geophysical data sets such as gravity data, magnetic data, seismic data, etcetera, and methods of geophysical modelling to investigate ocean basin formation processes and the influence of the Afar Plume on the evolution of the Red Sea.

So why is this work important?

The Red Sea has an important place in present-day plate tectonics because it is the only place where stretched and thinned continental lithosphere is transforming into the oceanic basin, pushing the African and Arabian plates away from each other. Thus, the Red Sea is a natural laboratory that allows geologists and geophysicists to test the recent concepts of the development of sea floor spreading.

In the northern part of the Red Sea, the continent is in an extension stage where African and Arabian plates are still attached without any oceanic crust forming in between. But the southern Red Sea has developed active sea floor spreading like any other oceanic spreading centre with continuous oceanic crust formation. Why they differ like this is still unclear to the geophysical community. The two important factors behind the divergence of plates are tectonism and magmatism. Fierce debates continue on both sides about the dominance of either of these factors over the evolution of the Red Sea. Through my research, I hope to provide some inputs to the scientific community that is interested in the evolution of ocean basins, particularly of the Red Sea.

Says Prof Murali Sastry, CEO of the Academy, “The IITB-Monash Research Academy represents an extremely important collaboration between Australia and India. Established in 2008, the Academy now is a strong presence in the context of India-Australia scientific collaborations. Sreenidhi’s project targets an area where limited research has been carried out. We wish her all success.”

The earth not only provides a home to us but also presents itself as a puzzle to enthusiasts through its infinite number of wonderful secrets. The anxiety to solve these puzzles is rooted in our unending love towards the earth. Geophysics is physics of the Earth, and we geophysicists try to study geological processes on the earth — whether its origin is shallow or deeper — using geophysical methods. I hope my research will add value to this vital and constantly evolving body of work on the evolution of the Red Sea.