This is an image the ocean floor of the Earth, showing trenches associated with island arcs.
Click on image for full size
Image from: NOAA/NESDIS/National Geophysical Data Center, Boulder, CO
Island Arc Formation
One of the processes of island formation involves lithospheric subduction. As a lithospheric slab is being subducted, a trench is formed at the interface with the adjoining slab. The slab undergoes melting when the edges reach a depth of the interior which is sufficiently hot. Hot, remelted material from the subducting slab rises and leaks into the crust, forming a series of volcanoes on the other side of the trench, each associated with the subducting slab of lithosphere.
Island Arcs are formed on the opposing edge of a subducted slab by a series of volcanos which pour out enough material to form substantial amounts of land. Examples of island arcs are the Japanese islands, the Kuril Islands, and the Aleutian Islands of Alaska, shown here. In each case, there is an associated subducting slab and a trench. The trenches for these island arcs can barely be made out in this map.
The second way in which islands are formed is via plumes or hot spots in the lithosphere. The Hawaiian Islands are an example of this type of island formation. In this case, there is no associated subducting slab nor trench.
Shop Windows to the Universe Science Store!
Learn about Earth and space science, and have fun while doing it! The games
section of our online store
includes a climate change card game
and the Traveling Nitrogen game
You might also be interested in:
When two sections of the Earth's lithosphere collide one slab of lithosphere can be forced back down into the deeper regions of the Earth, as shown in this diagram. This process is called subduction....more
Volcanoes form when hot material from below rises and leaks into the crust. This hot material, called magma, comes either from a melt of subducted crustal material, which is light and buoyant after melting,...more
The Hawaiian Islands are an example of the way some volcanoes are made. A rising hot plume of material makes it's way to the lithosphere of the Earth from the deep interior, and erupts material unto the...more
Ash is made of millions of tiny fragments of rock and glass formed during a volcanic eruption. Volcanic ash particles are less than 2 mm in size and can be much smaller. Volcanic ash forms in several ways...more
Cinder cones are simple volcanoes which have a bowl-shaped crater at the summit and rarely rise more than a thousand feet above their surroundings. They usually are created of eruptions from a single vent,...more
Lava can move in broad flat lava flows, or it can move through constrictive channels or tubes. Lava flows have a large surface area so they tend to cool quickly and flow slowly. The fastest unconstricted...more
Earth’s center, or core, is very hot, about 9000 degrees F. This heat causes molten rock deep within the mantle layer to move. Warm material rises, cools, and eventually sinks down. As the cool material...more