Does some of the ocean water go into the mantle during subduction, if so, does the weight of the ocean affect.
459846
Not much water in the form of free liquid water entrapped in pores of the rocks in subducted lithosphere that makes it into the mantle. However, the subducted plate *does* contain a substantial amount of water in the form of hydrous minerals  (e.g., clays, serpentine, amphiboles, chlorite, epidote, micas, etc.) that form by hydrothermal alteration of the oceanic crust, and are present in the overlying sediments (some of which are subducted).\n\nMuch of the water in these hydrous minerals is released when the subducted plate heats up as it is warmed by the hot mantle surrounding the plate, and the hydrous minerals dehydrate (really just a special type of prograde metamorphism).  The water that is released is thought to leave the plate itself and rise (because it is less dense than the rock, and hence bouyant) into the overlying mantle.  Water reduces the temperature at which  silicate rocks begin to melt, and because the mantle overlying the subducted slab is actually hotter than the slab itself, this water can trigger melting in the mantle.  This is why there is almost always a volcanic front above a subduction zone (e.g., the "Pacific ring of fire").  The magma associated with these subduction-zone volcanoes is usually volatile-rich (water and CO2 coming from hydrous minerals and carbonates in the subducted slab), and gives rise to explosive eruptions like Mt. St. Helens, or in a more extreme example, Krakatoa.
500218
The correct answer is C.  This is referred to as the rheological division of the mantle, as opposed to the chemical division (which puts the mantle into reservoirs such as MORB, HIMU, etc.)  The lithosphere behaves rigidly wheras the asthenosphere behaves plastically.
751689
The crust and mantle are generally solid.  The inner and outer core are molten rock and metal...very dense, but still liquid.
44246
mantle\nThe Mantle. It is divided into two parts. The upper portion, which is called the Asthenosphere, is a plastic like fluid. This is where the mantle convection currents occur. The rest of the mantle is made up of dense rock. The mantle is the thickest layer. Approximately 2900 km thick
24692
The best answer from the above choices: \nSlow moving convection currents within the molten aesthenosphere supply new material to the spreading centers in the earth's ocean floors and other places. These currents are thought to provide force to cause the motion of the oceanic plates, either directly, or indirectly through the mid ocean ridge building process. \n\nSubduction is only one part of the process of plate tectonics, that does provide some driving force by pulling the subducting plate downward. \n\nGravity has a role as well, as without gravity, the mid-ocean ridges would not have the weight to provide force with which to push the plates apart at the spreading centers, and the subducting plates would not have the force to pull plates. \n\nThe earth's magnetic field may have the least to do with plate tectonics, possibly no role at all.
147972
Water.\n\nWater is one of the key parts of the formation of magma in subduction zones. The water that is in the subducting plate lowers the melting point of the rock by a few hundred degrees C. The water in the subduction plate will boil and migrate upwards into the overlying wedge of mantle rock where it will reduce the melting point of the overlying mantle. This magma will migrate upwards and form a volcano. \n\nAnother part of this process is that within rock there are many different minerals, all with different melting points, so the ones that melt at the lowest temperatures tend to form magma first, so the resulting magma comes from a partial melt of the source rock.\n\nHere's another diagram (I'd draw you my own but I can't post anything but text here):\nhttp://earth.leeds.ac.uk/dynamicearth/subduction/cordillera_islandarc.htm
74571
The amount of mass moved by tectonic movement is much greater than the comparatively tiny mass e.g. taken out at Kiruna.\n\nLocally, where a whole mountain is shipped away, the ground may re-adjust to the new weight distribution on the plate. This is a maximum movement of centimetres, and applies to a plate swimming on a liquid.\n\nIf the earth was solid through and through, I think the mass centre might have moved a few millimetres  away from Kiruna, unless someplace in New Zealand or Polynesia was exporting huge amounts of Phosphate or other minerals. With a liquid interior, that effect will disappear.
703439
the core of the planet is said to be liquid under pressure, hence volcanoes.  the earth isn't hit with enough meteors etc to much influence the mass of the planet, but as the sea-floor dictates, can change in size.  an example is the two of the main plates, I believe in the area of the pacific rim.  these two plates are moving apart, at times exposing the hot core which pushes its mass into the cracks and cementing the 'spread' of the two plates. \nif the other plates of the planet move likewise, then yes, the world could increase in volume, and give rise to a bigger earth, in lieu of magma escaping from our depths, or by areas of the earth becoming less in depth to the core, like an icecube in a glass of water. \nsci fi of years gone by have mentioned the core in relation to volcanoes.  the implication was that the volcano activity was putting extreme pressure on our core, which if not filled by natural forces, would create a partly filled container under pressure.  the natural result was thought at the time was that the earth would explode or implode.
369103
Well, the upper mantle, more specifically the asthenosphere, is a plastic- by which I mean solid but able to flow- layer on which all of the crustal plates "float". Therefore, you can say that the asthenosphere is responsible for continental drift, and is thus the direct cause of earthquakes, volcanoes, and all other geologic events on our fair blue planet. Come to think of it, the mantle can be said to be one of the factors that influenced life itself in its long development over the past 3.8 billion years! As the earth's crust cooled, volcanoes-caused by upwellings in the mantle- released carbon dioxide and other compounds into the primordial atmosphere that were used by early life for nourishment. They also released a portion of the water vapor that now exists as a liquid across 2/3 the Earth's surface as water. Therefore, the mantle, in a way, is directly related to the origin of life, and, in turn, human life.
26232
Absoutly, there is a ridge subduction zone off the pacific coast that is moving at a good clip.  We know through laser tomography, that the surface of this subduction zone isn't as smooth as many other fault lines.  We know what will happen as soon as it 'buckles', a huge earthquake, followed, of course by a sub surface wave, making a tsunami.\n\nAs to when, no clue.  The plate at the subduction zone isn't moving at a constant clip, but random.  So hard to say.  Will it happen? Absoutly, when? Dunno.
713171
No the molecules still weigh the same. With water the volume will increase, that's why ice floats. Most other substances decrease as they freeze.
155676
This is the Wilson Cycle, and it is driven by plate tectonics. \n\nContinents are composed of relatively light weight felsic igneous rocks such as granites and granodiorites. Ocean basins are composed of mafic igneous rocks like basalt and gabbro that are heavier than continental crust. Since the earth's mantle is plastic, these different masses of rock tend to 'float' at different levels. This is called isostacy.\n\nOceanic plate motion originates at the mid-ocean ridges, pushing oceanic plates outward towards the continents. This motion and force is far from being uniform from one ocean basin to another, and is not even consistent along the length of the mid-ocean spreading centers. \n\nWhere oceanic plates meet continental plates there is a convergent plate boundary and generally this leads to subduction of the oceanic plate. There is considerable force however, and the style of subduction does vary. Since the forces that are being applied, as well as the resistance of the continental plates all are varied, there are inequities that cause the continents to move in one direction. Eventually this motion results in a collision of continents called a supercontinent because continents will not subduct under one another. India and Asia, and the Himalayas are a great example of a continental convergent plate boundary. Eventually the convection forces that cause the supercontinent to form will begin rifting it apart again creating new smaller continents. \n\nHere is a model of the Wilson Cycle:\nhttp://csmres.jmu.edu/geollab/vageol/vahist/wilsonsimp.html
30206
Convection in the asthenosphere (upper mantle)?
60681
If tectonic plates move underwater it is possible to get a Tsunami (Means harbour Wave in Japanese) anywhere assuming the conditions are right.\nGenerally Tectonic plate shifts have to occur in the up/down motion (Regional uplift or subsidence) to cause a Tsunami. Once the underwater wave hits shallow water it will raise the sealevel due to the force of the underwater wave causing a Tsunami.\n\nThe West coast of the US would be at most risk from a Tsunami due to the Pacific rim being a hot bed of Tectonic  plate activity, in fact they already have a Pacific Tsunami early warning system (USGS).\n\nI am no expert but have seen countless documentaries and read books on the subject.
209077
THere are layes of the ocean with differing salinity (salt) concentrations.  I don't think that a layer as you described could exist.  Buoyancy is a result of several factors.
331558
Oceanic crust is generally thinner since it is closer to the mantle, more dense since it is composed of mainly mafic basaltic rocks (have more ferromagnesians in them, i.e. iron) , and younger than continental crust since it is in a constant state of change near subduction zones and gets reformed sooner and more often then continental crust.
327692
because there is a subduction zone. One plate goes under the other and melts into the earth's mantle.