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Why the sands of the Maldives and Lakshadweep are white

The Maldives and Lakshadweep share a natural history and owe their beaches to the same fish that munch on coral

Kavaratti Island, Lakshadweep.
Kavaratti Island, Lakshadweep. (iStockphoto)

We are standing on a beach rather unique to these islands. How this sand was created is a remarkable story, and quite different from what we left back home. Most beach sand of continents is quartz and feldspar rich, formed by the degradation of ancient rocks like granite and quartzite. The beach sand here in the Maldives is white, powdery and vastly different from what’s found on continents. So how did this island beach come to be?

Until 88 million years ago, the eastern margin of Madagascar was melded to India’s west coast. An abrupt volcanic event tore Madagascar from India and broke off a small triangular piece from its north to create what we now know as Seychelles.

About 20 million years ago, when India drifted 900km away from Madagascar, another volcanic event was triggered under the sea. This created Reunion Island, which is now roughly 3,300km south-south-west from the Maldives as the albatross flies. This event marked the first of three episodes of what geologists label the “Deccan volcanic event”, which created Mumbai and Pune with its dramatic layered-cake plateaus.

Also read: Counting the environmental cost of India's investment in the Maldives

The volcanoes under the sea pushed the Indian plate further east. When India reached the spot where Chagos Islands (a corrupted version of the Portuguese word for chaos) are today, it tripped on another weak spot in the crust under the ocean, causing more lava to flow into the ocean. The roiling lava cooled in the presence of water and formed funnel-shaped structures that emerged from the sea. Each of these dark grey basalt cone-like structures spewed smoke and gas, and often lava. As India migrated northwards, volcanoes popped up and created a near-straight underwater ridge. This ridge, the 73 East Ridge, about 1,200km south of the Maldives, starts with Chagos Islands and ends with the Lakshadweep Islands (about 900km north of the Maldives).

For about three million years, the underwater volcanoes, where Chagos, the Maldives and Lakshadweep are today, poured out magma. Together these nudged and pushed the Indian Plate northwards. Thus, in a short geological time, the Chagos-Laccadive ridge, with the Maldives sitting in the centre, was created.

Under the widening Indian Ocean, another straight-lined ridge, the 90 East Ridge, was formed along the eastern margin of India on which the Andaman Islands emerged. Viewed from space, the Chagos-Laccadive and 90 East ridges appear like “draglines” or tracks on which the India Plate journeyed north, until it docked inside Eurasia. While the Andaman Islands are still seismically active, the Chagos-Laccadive are dormant. The only threat to the Maldives archipelago is a small active fault, which lies to its west—one needn’t worry too much about it. So, the Maldives and Lakshadweep, geologically, are cousins once removed. They were birthed and berthed at the same time—and both these islands are so similar because of their shared natural history.

A resort in the Maldives.
A resort in the Maldives. (iStockphoto)

Bubbling beneath

Between 60-48 million years ago, the volcanic activity subsided. Islands like the Maldives and Lakshadweep were a chain of small volcanic vents, a few of which rose above sea level. Small spurts of volcanic activity leached out nutrients and gases from the young porous basalt. This helped marine life to colonise the rocky rim. In a short time, giant coral reefs emerged along the rocky rims and slopes of the volcano. As the level of magma receded, the chamber which supported the top of the volcano (or the dome) sagged and caved in. Seawater invaded this hollow space and copious colonies of corals filled this void. We can see the hollow domes in these islands as deep blue lagoons, as one flies over these islands. It took about 12 million years or so for marine creatures to produce enough shelly calcium carbonate that it filled up these hollows. The white sands you see are the crushed, pulverised and powdered coral and shelly creatures.

Scientists who study these islands have found that the calcium-producing communities prospered in three distinct phases. The first phase was from 46-35 million years ago when the volcanic activity was receding. The second episode between 14-2 million years ago saw marine creatures reach the height of their productivity. The third, when the South Asian monsoon intensified, it flushed sediments down the Indus river to reach as far as these islands. New minerals spurred the growth of new life forms. All this helped create more calcium carbonate, which filled the deep, hollow lagoons of these volcanic islands. The coral reefs along the fringe acted as props for more carbonate.

Around 2.6 million years ago, when the Americas merged, it changed the ocean currents between the Atlantic and the Pacific. As new ocean currents formed, the Earth cooled, and ice caps reached the interiors of the northern continents.

Only around 14,000 years ago, after the ice cover had receded, did the oceans begin warming up. Between 11,000 to 4,000 years ago, conditions became ideal for coral and other marine creatures to resume their frenetic activity. The coral ring-fence accumulated more carbonate inside and around the lagoons, and these were filled by denuded carbonate.

The islands of the Maldives and Lakshadweep are just 5,000-3,000 years old, roughly the time when the Mesopotamian civilisation was getting established, which makes it among the youngest landmasses in the world.

So what has created all this sand? We see coral strewn on the beach here and imagine that it is this that degrades and becomes sand. This is partly true, but not quite. One fish, in particular, the parrotfish, eats mature coral and excretes calcium carbonate. This excretion appears like snowflakes in water. Parrotfish graze and munch on polyps of mature coral, and excrete so much sediment that they have created several Hawaiian beaches.

Off the tiny island of Vakkaru in the Maldives, geologists estimate that these fish excrete about 685 tonnes of sand each year. There are also some sponges and algae which bore into the coral, causing them to break and become beach sand. Not all coral-laced volcanic islands produce the same type of sand. In Kiribati island in the Pacific, the beach sand is made up of 37% coral fragments, 30% mollusc shells, 12% foraminifera, and 20% calcareous algae. In the Maldives, there is more coral (70%), calcareous algae (roughly 8% from the genus Halimeda), and a few shelly molluscs on its beach sand. Thus, each carbonate island has its own characteristic white sand, created by its own set of corals and creatures that feed on them.

Over the past 4,000 years or so, these islands have been colonised by seafaring plants like palms and Pandanus (a screw pine which produces aromatic kewra) whose seeds came ashore with tides and currents. A few creatures rode in as flotsam like shrews, geckos, and millipedes. The process of colonisation is still in progress. Life forms that arrive on these islands will evolve new survival strategies, albeit too slowly for our mind’s eye to perceive.

Human colonisation, especially lavish resorts, will stop nature’s process of colonisation and evolution. These pristine islands are young and are still evolving and need to be left alone. As sea levels rise and threaten these islands the world over, there are creatures like the parrotfish whose significance transcends all life on sea and land. Preserving the parrotfish and corals are crucial not only for future island building. They are the embodiment of how little we know about how nature works and what lies beneath its immense beauty.

Pranay Lal is a biochemist, a public health specialist, a natural history writer, and the author of Indica: A Deep Natural History Of The Indian Subcontinent and Invisible Empire: The Natural History Of Viruses. He is passionate about ecological restoration and reversing climate change.

Also read: Why Lakshadweep is an archipelago in climate crisis




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