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Discovering How Islands are Formed -min||Continental Island|barrier island|coral islands

Nature & Outdoors

How are Islands Formed?

There is something fascinating and mysterious about islands that have captivated the mind and imagination of humanity for a long time. Swarthy mariners listening to whispers of undiscovered continents across the ocean are filled with the same compelling determination. Invariably, little care is given to life and limb when setting out to uncover the secrets of these secluded lands.

Islands are more than just slabs of rock or mud poking out of the surface of the water, though they often spring from such humble beginnings. As the renowned scientist Charles Darwin found on his trip to the Galapagos Islands, these secluded locations provide a unique environment which presents its own tiny ecosystem and evolutionary path for the local plant and animal life. 1

In the early days of ocean exploration, the Polynesians followed the many strings of islands in the Pacific, called archipelagoes, to spread their seafaring cultures to the most remote islands. Island hopping would continue to the 20th century when locations like Tahiti, Seychelles, the Canary Islands, and Madagascar made important stops along trade routes that connected distant lands before the advent of flight and modern shipping. 2 , 3

Pirates who haunted these trade routes would seek out remote islands to stash their trove of treasure for later distribution. Pirate troves have been found across the globe and many are still waiting to be found. Some of the most famous pirate treasure islands include Oak Island in Canada, Ailsa Craig in Scotland, as well as thousands of desert islands up and down the Yucatan Peninsula and the rest of the Caribbean.

It may interest you to know that a desert island doesn’t necessarily have desert features, but a complete lack of human presence. In the Caribbean, less than 10% of the entire number of islands are actually inhabited by humans. 4


Island Geography

Islands can come in many different sizes and shapes and exist in any part of the Earth. Continents, even though they are expansive, are still surrounded by massive bodies of water and are therefore the largest islands on the planet. The largest land mass in the world still considered an island is Greenland with an area of over 800,000 square miles. The smallest continent is Australia with about 3 million square miles. But other than size is there another special reason Greenland and Island and Australia a continent?

It is not only the size of the landmass that determines Australia’s place as a continent. Unlike Australia that sits on its own tectonic plate, Greenland is still joined to the rest of the continent all the way down to Central America. Furthermore, there is hardly any major differences between the flora, fauna, and peoples of Greenland and N. America. The same can’t be said of Australia and its neighboring nations. 5

Island Formation

Perhaps the most fascinating part of studying an island is spectating on how this piece of earth came to be disconnected from the rest of the mainland. There are actually 6 different types of islands classified by the way they were formed.

Continental Island

Continental Islands

Continental islands may be several miles off the mainland but are still connected via the great tectonic plates below the ocean floor. The formation of continental islands can be accomplished a number of ways.

The British Isles are continental islands and were once connected to the rest of mainland Europe by a series of low lying regions. These lowlands were inundated over 18,000 years ago when the earth experienced temperature changes that released water that frozen in Glaciers toward the end of the last Ice Age. As the water levels began to rise, the British Isles gradually became cut off from the rest of Europe. There are actually several areas of low-lying Europe that should be underwater creating more islands but are prevented from doing so through advanced dams and levees. 6

The continental islands of Greenland and Madagascar were formed by great upheavals in the continental shelf to which they were once connected . Experts believe that all the Earth’s landmasses were once huddled together in a great supercontinent called Pangea which then broke up into smaller supercontinents called Laurasia and Gondwana.

During this movement, large pieces of land were snapped away from the rest. Because they are still connected to the continent, Greenland and Madagascar are two of the largest continental islands on the planet.

New Zealand sits on its very own micro-continental shelf which was once a part of Australia. Broke away from the rest of the continent roughly 80 Million years ago and has since become mostly submerged, except for the North and South Island and over 600 smaller islands scattered about the region. This type of formation is called a crustal fragment, but leading Kiwi Geologist Nick Mortimer believes that New Zealand ought to be the World’s 8th continent. 7

Many smaller continental islands can be formed when erosion gradually submerges a piece of land that connected a peninsula to the mainland. This often creates our next type of island, the tidal island.

Tidal Islands

Tidal islands are not always islands. As the tide rises and falls the connection between the island and mainland, called an isthmus, becomes apparent. Roads are even accessible across the isthmus at low tide. But once the tide comes back and the island is cut off this creates some marvelous spectacles that attract the curious and adventure seekers. Jindo and Modo in South Korea are famous for the Jindo Moses Miracle that creates a wide path between these two islands once the tide has dropped low enough. 8

barrier island

Barrier Islands and Fluvial Islands

Barrier and fluvial islands run alongside coastal and river borders and are usually the result of large deposits of sand, silt, gravel, or sediment that is carried along by natural forces. Sometimes these are located around protrusions of the continental shelf and other times can pile on top of coral reefs to form another type of island.

These are often called barrier islands because their strategic location can help to dampen the harsh winds and strong waves that come from the open sea protecting the mainland. The expanse of water separating the barrier island is called a sound or a lagoon. These were great places for ancient sailing vessels to wait out bad weather.

If a river island was created by sediment washed down the river, they can also be called fluvial islands. The largest river island in the world is could either be Majuli Island in the Brahmaputra River in India and Marajo Island in the Amazon delta in Brazil. While the Guinness World Records still lists Majuli as the largest river island, severe erosion has reduced its size and reportedly Marajo is now the larger of the two. 9 , 10

Unfortunately, the same forces that create fluvial islands can begin to erode them soon after. But there are other ways that barrier islands can be formed.

Glaciers are slow-moving rivers of ice that carve their way across a landscape creating beautiful canyons, majestic mountains, and cringing away great deposits of stone and dirt and other minerals it has carved from the Earth. Many of the largest glaciers of the last ice age carried their deposits of minerals to the sea where they collected in large heaps. As the ocean levels rose, these deposits became separated from land. Long Island in New York is one of the most famous islands created by a glacial deposit, or moraine. 11

Oceanic or Volcanic Islands

Most islands are formed close to the mainland where they can count on the continental shelf for a boost when extending well above the high tide mark. But no matter how close or far they are from the shore, volcanic or oceanic islands are called high islands as they typically rise high from the sea and often higher than 2000 meters. Even though they are sometimes much higher than volcanic islands, continental, barrier, tidal and coral islands are commonly called low-islands.

Oceanic volcanoes begin their life far below the surface of the water as seismic activity releases lava through fissures on the ocean floor. As time goes by, more and more layers of volcanic matter build up. A growing island is called a seamount before it eventually bursts forth out in a towering pillar of steam and fumes that can be seen for miles across the ocean waves.

In 1963 on the 14th of November, such a phenomenon was witnessed on a small island south of Iceland. Within 16 days the small steaming cloud of vapors revealed a sizable land formation, which was named Surtsey after a Norse Fire God. Since then, Surtsey has grown to a height of 155 m above sea level with more than 0.5 square miles. 12 , 13

This is a perfect example of how many of the most populated islands in the world came to be. Indonesia contains one of the most populated volcanic islands in the world, Sumatra. The islands of Japan, Taiwan, and Hawaii are also volcanic Islands. As volcanic islands age they can begin to sink back into the ocean leaving behind rich mineral deposits that attract corals if the conditions are right. This gives birth to a new type of island: the atoll.

coral islands

Coral Islands

Coral Islands can form in shallow tropical water that are conducive to the proliferation of tiny sea animals called polyps. These polyps can develop a strong exoskeleton calcium carbonate and then stack themselves into dainty structures that are more suitable to feeding.

These structures continue to grow and become populous oceanic areas where all sorts of marine life live and eventually die. The corals themselves eventually die under the weight of the ocean and the corals stacked on top. This compresses the corals and other shellfish corpses into towering mounds of limestone, onto which more coral can be added.

Eventually, the reefs become so large that they break the surface of the water and begin to collect sand and other organic and inorganic materials. Soon trees and plants begin to live and die on the island leaving their materials behind and adding to the composition of the soil. Then, coral islands are born.

The islands of the Caribbean and Bahamas are famous coral islands that attract tourists from around the world to bask in their tropical beauty and sparkling white sands. 14

Artificial Islands

Artificial islands are not made by any natural causes but rather the need for human expansion. Most often this has been done to expand existing land for purposes of development. This has been done with a great deal of efficacy from the time the early Nahua people founded what would become Mexico City on Texcoco Lake to the Dubai Waterfront, which will be the largest artificial island ever built. 15 , 16

Final Notes on Island Formations

The isolated situations of an island allow it to become the special home for a unique ecosystem, many of which we are still learning about. As these are such popular destinations, it is essential that they are also protected and respected as the natural treasures they are. If you have a heart set for island exploration the world is full of them but be sure you leave the place as immaculately clean, or better than when you found it.

Photo credits: VibrantImageStudio/, SteveLovegrove/, EvgenyGorodetsky/, RMcIntyre/, AndrewMayovskyy/

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