These hazards affect millions of people around the world, particularly around the edges of the Pacific Ocean, which mainly consist of subduction zones. The largest earthquakes on Earth occur at the interface between the two plates, called the megathrust. Recent examples include the magnitude 8. Earthquakes are caused by movement over an area of the plate interface called the seismogenic zone. It is then released catastrophically in one or more earthquakes. Above and below this area on the fault, stress cannot build up, and the movement between the plates occurs relatively smoothly through time, and thus does not produce large earthquakes.
A good example is the subduction zone near Chile. The final sign is deep marine trenches. These are the best evidence of a subduction zone as they are visible evidence of the crease formed by subduction of a plate. The most famous is the Mariana Trench. This makes a lot of sense due to the geologic evidence of large impacts scattered around the world. Understanding how subduction zones work is important because it helps scientist to identify areas of high volcanic and seismic activity.
Monitoring these areas can help them warn people who live near them of imminent events and also people who could be affected by the side effects of such events such as ash clouds or tsunamis.
Subduction continues to be one of the most powerful and dynamic processes on planet Earth and as technology improves we can come to understand more about this amazing process. We have written many articles about the subduction zone for Universe Today. For example, here is one on the Ring of Fire and plate boundaries. Geological Survey Website. Listen here, Episode Plate Tectonics. The denser plate is the one that slips under the less dense plate; the younger plate is the less dense one.
The process is not a smooth one. The tectonic plates grate against each other, which often causes earthquakes. The plate that slips under does not stay that way.
Due to the heat caused by it rubbing against the other plate as well as the natural heat of the mantle, the plate melts and turns into magma.
The area where subduction occurs is known as the subduction zone. Volcanic Arcs: The basaltic ocean crust contains hydrous minerals like amphiboles, some of which formed by hydrothermal alteration as seawater seeped through hot, fractured, young ocean crust at the midocean ridge.
As the ocean crust sinks deeper into the mantle the pressure increases the temperature of the ocean crust rocks increases more slowly because rocks are poor conductors of heat. At depths of around km beneath the surface, the pressure is great enough for the hydrous minerals to undergo metamorphism.
The resulting minerals are denser and they don't contain the bonded water. This metamorphic dewatering process liberates water from the descending crust. The water gradually seeps upward into the overlying wedge of hot mantle. The addition of water to the already hot mantle rocks lowers their melting temperature resulting in partial melting of ultramafic mantle rocks to yield mafic magma. Melting aided by the addition of water or other fluid is called flux melting.
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