Subduction zones create what type of volcanoes

Courtesy of NOAA. The crustal portion of the subducting slab contains a significant amount of surface water, as well as water contained in hydrated minerals within the seafloor basalt. As the subducting slab descends to greater and greater depths, it progressively encounters greater temperatures and greater pressures which cause the slab to release water into the mantle wedge overlying the descending plate.

Water has the effect of lowering the melting temperature of the mantle, thus causing it to melt. The magma produced by this mechanism varies from basalt to andesite in composition. It rises upward to produce a linear belt of volcanoes parallel to the oceanic trench, as exemplified in the above image of the Aleutian Island chain. The chain of volcanoes is called an island arc. If the oceanic lithosphere subducts beneath an adjacent plate of continental lithosphere, then a similar belt of volcanoes will be generated on continental crust.

Sometimes, the slabs may tear, like a gash in wrinkled paper. Pieces of the sinking plate can also break off and fall into the mantle, or get stuck and founder. Subduction zones are usually along coastlines, so tsunamis will always be generated close to where people live, Titov said.

But the bad news is sometime a tsunami is generated. When subduction zone earthquakes hit, Earth's crust flexes and snaps like a freed spring. For earthquakes larger than a magnitude 7. However, not all subduction zone earthquakes will cause tsunamis. Also, some earthquakes trigger tsunamis by sparking underwater landslides. Whatever their cause, the tsunami threat from subduction zones is monitored by government agencies such as NOAA in countries around the Pacific Ocean.

Tsunamis may strike in minutes for coastal areas near an earthquake, or hours later, after the waves travel across the sea. As a tectonic plate slides into the mantle, the hotter layer beneath Earth's crust, the heating releases fluids trapped in the plate. These fluids, such as seawater and carbon dioxide, rise into the upper plate and can partially melt the overlying crust, forming magma.

And magma molten rock often means volcanoes. Looking at the Pacific Ring of Fire reveals the link between subduction zones and volcanoes. When runny basaltic magma erupts as lava, it pours out of the ground along long surface cracks or through volcanic vents and may be sprayed into the air as spectacular lava fountains.

Rivers of lava can flow over the ground or move more slowly as blocky masses bulldozing along. The eruption of intermediate and silicon-rich magma is very different. It erupts from vents, sometimes as lava, but usually the magma becomes solid within the volcanic vent, giving much more explosive eruptions. At constructive plate boundaries, the tectonic plates are moving away from one another. Volcanoes can sometimes form in these setting; one example is Iceland. Iceland lies on the Mid Atlantic Ridge, a constructive plate boundary, where the North American and Eurasian plates are moving away from each other.

As the plates pull apart, molten rock magma rises up and erupts as lava, creating new ocean crust. The island is covered with more than volcanoes. Some are extinct, but over 30 are still active. The majority of volcanism in Iceland occurs along volcanic rift zones that cut through the centre of the island. At constructive plate boundaries, also known as divergent boundaries, tectonic plates move away from one another to produce volcanoes.

Hot magma rises from the mantle at mid-ocean ridges, pushing the plates apart. The interaction of these two types of volcanism, over the last 15 million years or more, has created the island of Iceland.

Destructive, or convergent, plate boundaries are where the tectonic plates are moving towards each other. Volcanoes form here in two settings where either oceanic plate descends below another oceanic plate or an oceanic plate descends below a continental plate. This process is called subduction and creates distinctive types of volcanoes depending on the setting:. Volcanoes can form at subduction zones where tectonic plates are moving towards each other and one plate descends beneath the other.

This illustration shows ocean-continent subduction. Subduction provides a mechanism for introducing water-bearing sediments into the mantle. It is this process that allows the generation of magma at depth that feeds volcanoes that are formed at the surface. Note: There is a third setting of destructive boundary: continent-continent.

Here, the pushing together of two continental plates results in the mountain forming processes that shaped, for example, the Alps and Himalayas.