We all know what an island is: a piece of land, surrounded by water, that’s smaller than a continent. The United Nation’s Law of the Sea also adds that, to be considered an island, the given piece of land must also be capable of supporting a living economy—so a mere rock does not count. What may be less obvious is what a “continental island” is, because the term sounds like a contradiction in terms. It’s not; it’s merely a subset of islands.
To understand a continental island, you need to understand what the continental shelf is. Anyone who’s been to the beach knows that the end of land isn’t a sudden cliff—around the edges of continents there is a stretch of gradually declining land, as pictured here. This area is called the continental shelf.
A continental island is simply an island that rests on the continental shelf. Because of this, these islands are always quite close to a given continent. Also, the water level around a continental island is very shallow, typically less than 600 feet.
The Canadian island of Newfoundland is a continental island, as is Greenland. Sicily, the ball being kicked by the foot that is Italy, is also a continental island. So is the African Republic of Madagascar, known for its distinct wildlife. Great Britain is the largest continental island in Europe.
Its believed most continental islands were, at one point, connected to their respective continents. Rising water levels are said to have 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 could reconnect these islands to the mainland.
A subset of the continental islands is the micro-continental island, formed by continents rifting—that is to say, when the Earth’s crust shifts to actually move a chunk of land away from a given continent. Madagascar is perhaps the best known example of this sort of continental island.