The island is part of the land, surrounded on all sides by water, and Peninsula water is not completely - he's kind of part connected with the land.
Often a result of the movement of the earth's crust some areas of land rise above the water and formed the island.
But the island where England and Ireland, was formed as a result of the reverse process. Long ago there was land. And so at some point fell, fell through a plot of land in the failure of the flooded sea water and cut off the land.
And it also happens. Volcanoes, many of which are under water, erupt, covering the seabed by a thick layer of lava. This process lasts for thousands of years, the layers grow and eventually appear above the water, forming an island. In this way arose the Hawaiian and the Kuril Islands. They still occasionally Wake up volcanoes.
Then there's the island, built by living creatures. There in the sea world of small marine inhabitants of the coral polyps. In sea water they extract lime from which to build houses-shells.
Live coral polyps, usually near the coast or in the warm upper layers of sea water, on the tops of seamounts. For many centuries the polyps build a huge number of houses-shells. Over time they break, become compressed, condensed, and on the tops of seamounts appear amazing fairy-tale structure. These structures grow and turn into a chain of rocks or small Islands. Such rocks are called coral reefs. Coral reefs are formed in shallow tropical seas. When the mass of corals begins to rise above the sea surface, it forms a coral island. Coral Islands annular shape are called atolls. Lake in the interior of this island is called lagoon.
The largest group of atolls on Earth - the Maldives, Laccadives, Caroline, and Marshall Islands.