How can a volcano become an island?

Have you ever stood on a beach, felt the warm sand under your toes, and looked far out over the waves? Way out in the ocean, there are little islands with no other land anywhere near them.

Picture one of them, a green hump of land with waves splashing all around it. Long ago, there was no island there at all, only deep blue water. So how can a volcano become an island?

Far beneath the ocean floor, deep inside the Earth, it is hotter than any oven. Down there, some rock gets so hot that it melts into a glowing, gooey liquid. We call it magma, which means rock that has melted deep underground.

Magma is lighter than the hard rock around it, a bit like a bubble rising in your bath. So the magma pushes upward, squeezing through cracks in the rock. At last it reaches the bottom of the sea.

When magma bursts out of the sea floor, we call it lava. The cold seawater cools the lava quickly, and it hardens into new dark rock. The spot where it pours out is an underwater volcano.

Again and again, more magma pushes up and spills out as lava. Each new flow of lava hardens on top of the last one, layer upon layer, over many thousands of years. Slowly the pile grows into a tall mountain hiding under the waves. What do you think happens if it keeps on growing?

The mountain grows so tall that its top pokes up above the water! Now there is dry rock you could stand on, with ocean all around it. The volcano has become an island, just like the islands of Hawaii.

A volcano becomes an island when hot magma rises through the sea floor and spills out as lava. That lava hardens into layer after layer of rock, until the mountain grows tall enough for its top to poke out of the sea.

Now waves splash against the dark rock at the top of the old volcano. Where there was once only deep blue water, a brand new island sits in the sunshine.