When you think about an island, visions of white sand beaches, tropical climates, and coconuts may be among the first things that come to mind. But the term “island” refers to any piece of land that is surrounded by water, and there are thousands of islands located all around the world.
Islands can be small or large, warm or ice-covered, and some are inhabited while others are barren lands with little more than some rocks and shrubbery. Many islands boast rare biodiversity due to being isolated for longer periods of time than most continents; even two islands near each other are likely to have vastly different flora and fauna.
Of the countless islands that exist in the world’s oceans, most can be categorized into six major types. We’ve outlined these six categories below so you can discover these types for yourself.
Table of Contents
1. Continental Islands
A continental island is an island that at one point in time was connected to a continent. Scientists believe that long ago, there was one large continent, Pangea, and after a series of slow movements broke the earth’s crust apart, this massive landmass had large pieces of the earth break away from the main continent. Many of the world’s largest islands were formed this way, and some of the most well-known examples include Madagascar and Greenland.
Continental islands can also be caused by rising sea levels, and after the most recent glacial period (some 18,000 years ago), glaciers melted and flooded many low-lying areas of land. This type of continental island is usually found in shallow seas off of large landmasses. The best example of this is the British Isles, which were once connected to Europe’s mainland. If the earth continues to warm and polar ice caps continue to melt due to climate change, we may see more islands being formed this way in the future.
The third and final way a continental island can be formed is by extreme weathering and erosion of the land that once connected islands to the mainland.
2. Tidal Islands
A tidal island is technically still connected to the main continent, but that connection sits below the water at high tide. These types of islands are highly influenced by the tides but can sometimes be accessed by the natural connection to the mainland during low tide. Many tidal islands are now connected to their mainland via artificial causeways, allowing traffic to flow to and from the island no matter if the tide is high or low.
Tidal islands are one of the most common types of islands in the world, and some of the best examples of this island type include Mont Saint-Michel (connected to France’s mainland), Jindo and Mondo (connected to mainland South Korea), and Cramond Island (connected to Scotland’s mainland).
3. Barrier Islands
Barrier islands are aptly named, as these narrow landmasses often protect the coastlines that are nearby. While some barrier islands are part of the continental shelf, many are made from sand, sediment, silt, and gravel caused by ocean currents. But the same systems that build these types of islands can also be what destroys them, and barrier islands are subject to change during severe weather. San Padre Island and the Outer Banks of the United States are both great examples of this type of barrier island.
This type of island can also be formed from materials deposited by melting glaciers, such as rock, soil, and gravel. These deposits of debris are referred to as moraines, and some of the most famous of this type of barrier island include Long Island in New York and Nantucket off of Massachusetts.
4. Oceanic Islands
Oceanic islands are formed from volcanic eruptions on the ocean floor. For this reason, they are often referred to as volcanic islands, and these types of islands are often very far away from larger landmasses. As an underwater volcano erupts, layers of lava build up and may or may not break the surface of the water. Those that do come out above ground are referred to as oceanic islands, while those that remain below the surface are known as seamounts (or underwater mountains).
Different types of underwater volcanoes form different types of oceanic islands. The volcanic activity that results in tectonic plate movement, specifically when one plate slides underneath another, can result in an oceanic island being created. The island of Japan is one of the best examples of this, and this nation sits on four volcanic plates. Other oceanic islands created by the subduction of plates include the Mariana Islands and the Republic of Mauritius.
Another type of underwater volcano that can create oceanic islands occurs when two tectonic plates split away from each other, causing a rift that eventually reaches the surface. Examples of these types of islands include Jan Mayen, Surtsey (the world’s newest volcanic island), and Iceland (the world’s largest volcanic island).
Oceanic islands can also be formed by hot spots, which occur when a break in the earth’s crust allows magma to travel towards the surface. This usually results in a line of islands, and one of the most famous chains is the Hawaiian Islands. This type of volcanic activity can take millions of years to complete, and Loihi (the “newest” Hawaiian island) is still above the volcanic hotspot that created all the other islands, though it has yet to break the surface.
5. Coral Islands
As the name suggests, coral islands are made up mostly of coral, which are tiny sea animals that build hard exoskeletons of limestone (or calcium carbonate).
Coral reefs grow along the bottom of the seafloor, and some get so big that they eventually break the surface of the water. Once this happens, they are considered coral islands. Other materials (both organic and inorganic) can aid in the creation of these unique types of islands. The most famous chain of coral islands is without a doubt the Bahamas, located in the Caribbean Sea and the Atlantic Ocean.
Atolls are another type of coral island as this type also gets its start as a coral reef. The difference is that atolls form around volcanic islands, and once the volcano begins to sink, the coral reef continues to grow until it rises above the water. This type of coral island is usually circular in shape and is most common in the Pacific and Indian oceans.
6. Artificial Islands
The last major type of island is the artificial island, a man-made landmass created for a variety of purposes.
One of the oldest artificial islands in the world was created in the 14th-century by the Nahua people. They found an existing island in Lake Texcoco (located in current-day Mexico) and expanded the area by draining part of the lake to create land for their capital city of Tenochtitlan. They also created roads to connect the islands to the mainland and aqueducts to provide water for all of the city’s 200,000 residents. This also created more arable land for planting crops and other forms of agriculture.
Another way of forming an artificial island is by bringing in material from elsewhere and piling it up to form a landmass. Dubai is famous for the luxurious Palm Islands that they have made from spraying sand from the Persian Gulf into the shape of palm trees, and once the waterfront of this modern city is complete, it will be the largest man-made development in the world.