They are great sources of new material for the Earth's crust and can create, not only one, but a chain of islands. .
The emergence of an oceanic volcano is only the beginning of an island chain. When a hot spot is active it will push magma up to the crust above, to create a volcanic peak if on land, or seamount if in water. The primary volcanoes on each of the Hawaiian islands are called shield volcanoes. They are described as gently slopping mountains, looking much like the outer surface of a shield lying on the ground. They are created by numerous lava flows that slowly spread out and harden in very thin layers (Rubin 1). After the building of layer upon layer the volcanoes eventually cut through the surface of the ocean forming an island (Rubin 2). The eruptions of shield volcanoes tend to have a quiet, smooth outpouring of thick, flowing magma rather than a sudden explosion (Duxbury 73). However, on occasion, some of the Hawaiian volcanoes, such as Kilauea, have produced large explosions. Explosions usually only occur when the magma mixes with groundwater, creating instant vaporization. Some of Hawaii's shield volcanoes have lava fountains that spew up from the top of the volcano that can reach as high as 400 meters (Monroe 89). The average Hawaiian volcano can remain active for hundreds of thousands of years before being carried away from its hot spot by the moving pacific plate (Rubin 2). The volcanic activity within the sea around the islands is believed to be a factor in the fact that the surrounding waters are about 83 degrees F year round. .
The plate tectonics of the Hawaiian Island region play a major role in the formation of this unique island chain. As the hot spot forms and fuels a volcano, the pacific plate is continuously moving westward. Since hot spots are stationary the moving plate carries the volcano with it, cutting off the constant supply of magma. Without the magma reserve the volcano can no longer erupt, leaving it inactive.