An island is a landform many recognize, though its precise definition is nuanced. While commonly pictured as land surrounded by water, distinguishing an island from other landmasses requires specific criteria. These characteristics clarify what truly qualifies a landmass as an island.
Essential Island Characteristics
An island is entirely surrounded by water. Water completely encircles the landmass, separating it from any larger landform. This fundamental criterion ensures the land stands alone within its aquatic environment.
An island must also be naturally formed. This differentiates true islands from artificial structures like those created by human construction or dredging. Natural geological processes are responsible for their formation.
An island must remain above the water’s surface at high tide. This differentiates islands from submerged shoals or sandbars that only appear during low tide. The land must be consistently exposed.
Islands also imply permanence and geological stability. While erosion and geological shifts can alter them, they are generally stable landforms, unlike transient sandbanks that frequently shift or disappear with currents and tides.
Islands Versus Continents and Islets
The distinction between an island and a continent revolves around size. Continents are vastly larger landmasses, defined by their extensive size and unique tectonic plate affiliations or continental shelves. For example, Australia is considered a continent due to its immense size and position on its own tectonic plate, despite being entirely surrounded by water.
Conversely, differentiating islands from smaller landforms like islets, rocks, or sea stacks depends on size and consistent presence above water. Islets are much smaller than islands, sometimes lacking vegetation or permanent human habitation. They must also remain above high tide to be considered stable landmasses.
Very small, often barren, landforms are classified as rocks or sea stacks. These are steep, often vertical, columns of rock near a coastline. While surrounded by water, they are too small to be considered islands.
Different Kinds of Islands
Islands can be categorized by their geological formation and relationship to larger landmasses. Continental islands are on a continent’s continental shelf. Islands like Great Britain or Greenland were often connected to the mainland, separating due to rising sea levels or tectonic activity. Their geology often mirrors the adjacent continent.
Oceanic islands form independently of continental landmasses, rising from the ocean floor. Volcanic islands are a common type, created by magma erupting from the seafloor. The Hawaiian Islands or Iceland are examples that grew from successive lava flows.
Another oceanic island type is the coral island or atoll. These form from accumulated coral skeletons and other organic marine debris, often building on submerged volcanic peaks. Many Pacific Ocean islands are coral atolls, characterized by a ring-shaped reef enclosing a lagoon.