There are various methods by which islands are formed and the prime among them is the volcanic eruption.
When a volcanic eruption happens it releases lava and several other substances from the crater. In due course of time the lava cools down and it turn into a solid. And the accumulation of all these solids is what makes an island. But it is not a process that is being done in a year or two but takes millions of years to form an island. There are several examples of the formation of the islands through this method and the prime among them is the islands of Hawaii. In some areas of Hawaii you can still find the volcanic eruption going on and it may happen that the size of some islands get increased or some other island may also formed soon.
There are three ways to form an island that I know of. The most obvious is the way that most Pacific islands are formed. Volcanic eruptions in the ocean begin to rise and form island land masses. Another method is that glacers melt carving out troughs in the soft earth's surface. The harder earth will stay above the trough. Water from the melting ice forms rivers and the solid ground that was not carved away will be surrounded by the river water. The third method is how Florida was formed. Swamps are created by constant rain falling on flat land. The trees in the swamp will either rot, falling into the water or begin to absorb the acidic water through their roots. Logs, mud, dead and decaying animals, etc will build up around these trees and other obstructions and eventually form humus, soil, bogs, and finally solid earth. Since the ground is higher than the surrounding swamp, streams will begin to flow to push the water off. These streams will eventually force more water into rivers which will flow out to the sea. After another millenia, an island or penisula is formed.
What many of you forget is that Hawaii is not your classic case of island-forming. Hawaii was formed as the tectonic plates moved over a hot spot of magma, and the magma burst through the plate. This is not your classic case. That's why Hawaii's special. Most Islands form from convergent (pushing together) plate boundaries subducting (one going under the other) and from immense heat and pressure, transformed into magma. This magma builds up, and eventually overcomes the strength of the tectonic plate and bursts through. This forms an active volcano, usually along what is known as the Ring of Fire. As some stated above, the volcano erupts, and grows larger and larger, eventually breaking the surface (if it was under water) and becoming and island. I hope this helped. I should know this, as I have a test on it tomorrow!
Islands are formed by a volcanic erupting and the lava comes down and waits and turns into solid and then a tsunami comes and it makes it grow plants and so then it might take a year or two but most of the times it takes like a million years for example hawaii is one
Of course volcanic eruptions is the main thingy But there are also two more Umm... One is that two tectonics plates smash together and form an island Somehow And Umm... Another is I don't know Can anyone tell me I need it for work I'm zoo dumb