Islands

An Island is a type of Habitat which is surrounded by water on all it's sides and is smaller than a Continent. Islands are found in Oceans, Seas, Lakes and Rivers all over the World. Canada probably has far more Islands than either country, as it has immense areas of Island-strewn lakes and thousands of miles of rocky coastline. Several small countries have no Islands at all. Very small Islands are known as Islets or Keys. A grouping of geographically or geologically related Islands is called an Archipelago. A Desert Island is an Island which is Uninhabited or is yet to be Inhabitable by humans. It is known as a Desert Island not because it has dry climate but because it is deserted, or abandoned. De Long Islands and Blasket Islands are some of the examples of a Desert Island. An Artificial Island is an Island  that has been constructed by humans rather than formed by natural means. They are created by expanding existing islets, construction on existing reefs, or amalgamating several natural islets into a bigger Island. Palm Jumeirah in Dubai and Northstar Island, an artificial Island for oil drilling in the Beaufort Sea, are some of the examples of  Artificial Island.

Classification / Types of Islands

1.  Continental Islands - Continental Islands are bodies of land that are connected by the Continental Shelf to a Continent. That is, these Islands are part of an adjacent Continent and are located on the Continental Shelf of that Continent. The Continental Shelf is a gently sloping and relatively flat extension of a Continent that is covered by the Oceans. Its believed most Continental Islands were, at one point, connected to their respective Continents. Rising water levels created them, typically by cutting off a former Peninsula or simply rising high enough to cover most of the coastal regions, leaving only the high ground as Islands. A drop in sea level can reconnect these Islands to the mainland.

• Microcontinental Island - There is also a special type of Continental Island, known as the Microcontinental Island, which occurs when a Continent is rifted. Examples are Madagascar and Socotra off Africa; New Zealand; New Caledonia; the Kerguelen Islands; and some of the Seychelles.

• Barrier Island - It is a long narrow sandy Island (wider than a reef) running parallel to the shore. It formed by deposition of tiny rocks where a water current loses some of its carrying capacity. They usually occur in chains, consisting of anything from a few Islands to more than a dozen.

Some Continental Islands

1. Greenland and Sable Island off North America.
2. Barbados and Trinidad off South America.
3. Sicily off Europe.
4. Sumatra and Java off Asia.
5. New Guinea and Tasmania off Australia.

2.  Oceanic Islands - Oceanic Islands are those that rise to the surface from the floors of the ocean basins. Most Oceanic Islands rise from the sea as a result of volcanic activity on the ocean floor. They do not have any links with the continents. Some oceanic Islands are built up around one or two volcanic vents while others, like Tahiti, are formed by a whole series of vents. As they emerge from Volcanoes, they are also known as 'Volcanic Island. At first such Islands are uninhabitable but gradually, as the lava cools, they begin to support life. Sometimes, coral Islands develop from reefs that form around the volcanic Island. The original volcano may sink following movements in the Earth’s crust, or due to rise in the sea level.

• Volcanic Island Arc - It is a type of Oceanic Island arise from volcanoes where the subduction of one plate under another is occurring.

• Hotspots - A Hotspot is more or less stationary relative to the moving tectonic plate above it, so a chain of Islands results as the plate drifts. Plate movement across a hot-spot produces a line of Islands oriented in the direction of the plate movement. An example is the Hawaiian Islands.

• Atoll - An atoll is an Island formed from a Coral Reef  that has grown on an eroded and submerged volcanic Island. The Reef rises to the surface of the water and forms a new Island. Atolls are typically ring-shaped with a central lagoon. Examples include the Maldives in the Indian Ocean and Line Islands in the Pacific.

Some Oceanic Islands

1. Mariana Islands.
2. Aleutian Islands.
3. most of Tonga in the Pacific Ocean.
4. Some of the Lesser Antilles.
5. South Sandwich Islands are the only Atlantic Ocean Islands.

3.  River Islands - River Islands occur in river deltas and in large rivers. They are caused by deposition of sediment at points in the flow where the current loses some of its carrying capacity. In essence, they are River Bars, isolated in the stream. While some are temporary, and may disappear if the river's water volume or speed changes, others are stable and long-lived. Sandwip Island, Richards Island, Majuli are some of the River Islands.

Major Islands of the World

• Borneo in Indonesia comprising Malaysia and Brunei.

• Greenland in North Atlantic Ocean.

• New Guinea in Papua New Guinea.

• Madagascar in Indian Ocean.

• Sumatra in Indonesia.

• Victoria Island in Northwest Territories, Canada.

• Great Britain, United Kingdom.

• Java in Indonesia.

• Newfoundland in Canada.

• Iceland in North Atlantic Ocean.

Distribution

Islands are located all over the world

General Characteristics of an Island

• Unique Species of Animals - Due to their isolation, Islands have unique Species of Animals that have evolved independently of relatives that live on the mainland. Coastal Island Animals have to deal with changes to their environment due to the tides. Some may be submerged in salt-water twice daily and left exposed to sun and wind for the rest of the day. Life further away from the coastline means that Animals may only be submerged in water twice yearly and those Animals living low on the coastline may be submerged for much of the year. Because Islands were originally populated with Animals before the land mass was separated to become an Island, the Animals there evolved independently of their relatives that live on the mainland. Australia, a large Continent, has a number of unique Animals such as the Kangaroo, Koala, Wallaby and the Echidna, which is also found on New Guinea. Madagascar has a unique group of primates called lemurs. Monkeys that evolved after Madagascar became an Island resulted in those primates being more primitive than Species on the mainland. Some Animals like Giant Tortoises of Aldabra, the Galapagos Islands and the Komodo Dragon found only on Komodo Island have evolved to become unusually large, perhaps because there is no competition from other Animals for space or food. Some are are endemic which means they are not find anywhere else. They don't migrate e.g. white starling of Bali.

• Unique Vegetation - A long-established sea barrier results in marked differences between the vegetation even of adjacent Islands, and from these differences may be deduced the origin of an Island. Approximately, 560 Species of Galapagos Plants live in the Islands, from which about a third are endemic (unique) to the Islands. Some of the Plants include giant prickly pear cactus, cherry-like tomato, a member of the daisy family that locally evolved into 17 different Species (genus Scalesia) etc. Catalina endemic Plants are Species that occur naturally on Catalina Island and nowhere else in the World.

• Prone to Tides - As Islands are surrounded by water they are prone to frequent high and low Tides. Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun and the rotation of the Earth. So at high Tide, a portion of an Island gets submerged in water and at low Tide the submerged portion is revealed. This has an effect on Plants and Animals who have learnt to deal with such frequent changes.

• Easily affected by Global Warming - Islands are also prone to destruction by human activities leading to Global Warming which is characterised by increase in temperature which affects the melting of polar ice and ultimately leads to rise in the sea level. This directly is consequential to an Island's existence. The recent disappearance of New Moore Island located in the Bay of Bengal, between India and Bangladesh is a direct result of Global Warming.

Origin of Islands

The first Islands appeared on Earth about 4.4 billion years ago, when the Oceans formed. However, most Islands now in existence are extremely young, the result of sea level changes and glacial retreat over the last 12,000 years or so. The Island that has existed longest is Madagascar, which separated from India perhaps 85 to 90 million years ago, after the two had split off from Antarctica about 125 million years ago.

Importance of Islands

• 1 of every 9 people is an Islander and 700 million people live on about 9,000 inhabited Islands.

• Islands also provide home to various Species of Plants and Animals which are not found anywhere else. Komodo Dragon and Marine Iguana are some of the Endemic Species found only in Islands.

• Islands are the Earth's great repositories of biological diversity. Their favourable climates and historic isolation have produced a great variety of Endemic Plant and Animal Species.

• The exclusive economic zones of Islands cover one sixth of the world's surface and harbour one half of its marine biodiversity. Many Islands are home to mangrove forests, the breeding grounds and nurseries for countless Species of Fish.

• Islands in the determination of the boundaries of Animal-life and vegetational types. For example, to the west of a line (Wallace’s Line) running between Bali and Lombok and between Borneo and Celebes, the Islands are biologically Asian, but to the east of the line, notwithstanding the narrowness of the Lombok Strait, the vegetation and Animal life are Australian.

• Islands are like open laboratories for researchers and scientists seeking answers to unsolved mysteries of life.

• A large number of tourists visit various Islands which generates revenue for the countries where they are found. Various water sports and other adventure activities attract a large number of people to the Islands.