May times they are so big, even the biggest volcanos on land look like dwarves. Sometimes their tops arise above the water and they form islands. These tops have grown for more than a million years to grow above the sealevel. Underneath the water a volcano is formed. The magma pushes the crust up.
Hot spots are isolated areas with volcanic activity in the earth.
Plumes of magma break through the bottom of the sea. Some hot Sommige hot-spots produce volcanos for more than 70 milion years. Volcanic islands can arise along the ridges in the middle of the oceans, where oceanplates give way to eachother and melted magma wells up out of the fracture-line. The magma is pilled up and in about thousands of years a volcanic island is born. A new-born island.