Lake island

A large volcanic eruption sometimes results in the formation of a caldera, caused by the collapse of the magma chamber under the volcano.

If volcanic activity continues or restarts, the centre of the caldera may be uplifted in the form of a resurgent dome, to become a crater lake island.

Due to the lack of currents and tides, these are more frequently found in lakes than in rivers or the open sea.

Peaty masses of vegetable matter from shallow lake floors may rise due to the accumulation of gases during decomposition, and will often float for a considerable time, becoming ephemeral islands until the gas has dissipated enough for the vegetation to return to the lake floor.

Artificial islands are built for numerous uses, ranging from flood protection to immigration or quarantine stations.

Other uses for reclaimed artificial islands include expansion of living space or transportation centres in densely populated regions.

Agricultural land has also been developed through reclamation of polders in the Netherlands and other low lying countries.

At 948 km2 (366 sq mi), Flevopolder, in the now-freshwater lake IJsselmeer, is the largest man-made island in the world.

Other islands are lost by sinking below the lake surface, either by erosion, subsidence, or rising water level.