describe the differences between the ridge push hypothesis and the slab pull hypothesis.?
828845
ridge push hypothesis sounds more appeling, besides that i don't know
320893
try this:\nhttp://www.seismo.unr.edu/ftp/pub/louie/class/100/plate-tectonics.html
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.
16395
This process is known as plate tectonics. The earth's surface is composed of large 'plates' which gradually move around over time. The movement is driven by convective currents of molten rock within the asthenosphere. Movement begins at the midocean ridges, which are actually larger than continental mountain ranges. As magma builds these ridges the weight of the material, combined with the convective flow causes them to push outward towards the outer parts of the oceanic plates. Some of these plates subduct (go under) the continental plates, or even other oceanic plates. This subduction process lifts continents higher and leads to mountain building. You can see some illustrations here:\nhttp://www.ucmp.berkeley.edu/geology/tecmech.html\nYou can watch animated versions showing the plate motion here:\nhttp://www.ucmp.berkeley.edu/geology/tecmech.html\n\nAs for parts of the earth falling into the ocean, that is just a not-so-serious thing that people say trying to explain plate tectonics. There are zones of continental crust that are rifting, being split apart, and these may eventually move below sea level. Some examples of this are the Great Rift Basin in northern Africa. The Red Sea is a rift zone that has submerged, and the Dead Sea is part of a rift zone. \n\nThese processes are quite slow on our time scale. The Pacific Ocean is spreading about 4-5 cm per year.\n\nAnd if you've ever heard that California is going to fall into the ocean- don't worry it isn't. The boundary between the Pacific Plate and the North American plate is actually within California, but the motion is such that Los Angeles is moving north towards San Francisco. Millions of years from now, Los Angeles may be moved north of San Francisco.
435645
A, because it's the division between two tectonic plates. the plates move apart and magma from inside the earth comes up and piles up in the form of mountains.
488071
At convergent plate boundaries two plates collide and the heavier of the two plates is forced beneath the lighter one. As the heavier plate gets pushed down deep into the earth it begins to melt and forms molten magma. This magma slowly migrates upwards through the earth's crust where it then errupts onto the earth's surface as lava, eventually forming volcanoes. \n\nAt divergent plate zones two plates move apart from each other. When this happens a crack forms in the earth's crust. Magma from below moves upwards into this crack to fill the void 'so to speak'. Once again this magma errupts onto the earth's surface as red hot lava and we have the formation of active volcanoes.
98234
The crust is way lighter than the rock of the lower mantle, and its volume is tiny in comparison. So if by "easily" you mean how much energy is required to move the rock, then the crust moves around much easier than the rock in the lower mantle.
97748
Sea floor spreading is driven by two things. Upwelling magma from beneath the crust erupts at these spreading centers, and pressure and heat from these forms a bulge and magma pushes the plates apart.  Spreading is driven by the mass of the region around the spreading center as it increases and slides off of the bulge pushing outward. At the opposite end of the oceanic plate, there is a pulling motion, caused by colder subducting slabs sinking downward into the asthenosphere. This push-pull motion sets up a gradual motion of the seafloor outward from the mid-ocean ridges. \n\nAnother mechanism that may be contributing to this movement is what is called friction of convection. As plastic nearly-molten rock moves through the mantle is may be dragging these plates along by fricton. Since the spreading centers are likely to be upwellings of deep hot rock, the flow would be moving away from these centers under the ocean crust and pulling it away from the centers.
214692
Slickenlines will give a direction of slip, but as you have probably thought out, that still has two possible interpretations. It isn't always easy, but there are several things you may observe that will help.\n\nSlickensides will also develop a series of small steps that show the sense of movement. These are somewhat perpendicular to the fault movement and the steps will be the trailing edge of the movement direction. \nHere is a picture, where the top (missing portion) side moved to the left. \nhttp://www.geo.cornell.edu/geology/class...\nHere are several other illustrations of these steps:\nhttp://www.geo.cornell.edu/geology/class...\n\nDrag folds will also help you determine the sense of movement. These folds are distortions of the bedding due to shearing along the fault. They are convex toward the direction of slip, with the exception of rollover anticlines along listric normal faults. To describe it another way, the shear will form a 'cup-like' pattern near the fault in the bedding, the bottom of the 'cup' will point toward the direction of movement. If on the upper side of the fault your 'cup' points downward, it should be a normal fault, and if this 'cup' points upward on the upper side of the fault, it is likely a reverse fault. \n\nUsing stratigraphic layers will often not get you much further than the slickenlines, giving you two possible directions. But, in some outcrops you can look at the topmost part of the fault and also see some evidence of the sense of movement by observing the most recent deposition or the thickness of the soil layer over the fault blocks. Where the fault blocks have been eroded away equally on both sides this may not help. \n\nIn other instances you may have to do more mapping and examine other faults in the area before you can make a conclusion. If you know the area is extensional, then you have a hypothesis to work with. The best idea is to always check as many kinds of evidence as you can find before you make a conclusion.
475416
Nope; the oceanic plates are spreading apart, as new material (magma) is pushed up from below.  They are not crashing together at all.
103247
The kind of force? This is normal force - the deformation incurred along a plate boundary (be it convergent or strike-slip) is caused by the repulsive force of particles of baryonic matter. It's the exact same force that is exerted when you push your hand against a wall.\n\nWhat drives plate motion is convection of the underlying magma, which is heated by nuclear decay deep in the earth.\n\nEarthquakes are the result of stored energy from continued strain on a region. They aren't really a force themselves, they are simply the result of a release of stored energy when rock surfaces slip suddenly and release P and S waves. (Along with a whole bunch of other waves, Love and whatnot, I can't remember everything)
1096356
Introduction\nPlate tectonics is a relatively new theory that has revolutionized the way geologists think about the Earth. According to the theory, the surface of the Earth is broken into large plates. The size and position of these plates change over time. The edges of these plates, where they move against each other, are sites of intense geologic activity, such as earthquakes, volcanoes, and mountain building. Plate tectonics is a combination of two earlier ideas, continental drift and sea-floor spreading. Continental drift is the movement of continents over the Earth's surface and in their change in position relative to each other. Sea-floor spreading is the creation of new oceanic crust at mid-ocean ridges and movement of the crust away from the mid-ocean ridges.
1023902
Key principles\n\nThe key principle of word formation is that the wordsphere exists as separate and distinct letter plates, which float on the fluid-like (visco-elastic liquid) phrasesphere. The relative fluidity of the phrasesphere allows the letter plates to undergo motion in different directions. One plate meets another along a plate boundary.\n\nTypes of plate boundaries\n\nThere are three types of plate boundaries, characterized by the way the plates move relative to each other.\n\n   1. Transform boundaries occur where plates slide, or perhaps more accurately grind, past each other along transform faults. The relative motion of the two plates is either sinistral (left side toward the observer) or dextral (right side toward the observer).\n\n   2. Divergent boundaries occur where two plates slide apart from each other (examples of which can be seen at mid-ocean ridges and active zones of rifting (such as with the East Africa rift)).\n\n   3. Convergent boundaries (or active margins) occur where two plates slide towards each other commonly forming either a subduction zone (if one plate moves underneath the other) or a continental collision (if the two plates contain continental crust). Deep marine trenches are typically associated with subduction zones. Due to friction and heating of the subducting slab volcanism is almost always closely linked. Examples of this are the Andes mountain range in South America and the Japanese island arc.
1117362
tectonic plates or continental drift
967662
It all comes down to stress and strain. It is not 'the plates rubbing together' as many people say; or at least that's a very simplistic view.\n\nPlate tectonics causes stress on the continents and oceans, all over the surface of the earth. In some places, the stress is very small (usually within the plates). Elsewhere, the stress is high, usually where the plates meet each other. Since each plate moves, when two come in contact, the stress each other. They can push on each other and cause compressional stress, they can pull with extensional stress, and they can slide past or shear each other with tensional stress.\n\nFaulting, causing earthquakes, comes from the fact that this stress is building up all the time, but rocks and continents are strong materials. Just like hitting a rock with a small hammer, you do put stress on it, but a small amount. It would take a sledgehammer to put enough strain (effects and accumulation of stress) to build up and cause breakage. In the earth, the area around an active fault builds up strain from the stress of plate tectonics. Most faults become locked, because of this strength, and thus can not release their strain. Away from the fault, the stress produces very small and slow movement of the rock masses as a whole. Eventually, the strain is too much and the rest of the plate has moved too far and the fault releases the strain build-up all at once in a big stress release called an earthquake. This is called the elastic rebound theory, and it explains most (but not all) movements.\n\nThis is why an earthquake's size is relative to the fault size. The bigger the fault, the bigger the strain build up, and the bigger the release in an earthquake. Subduction zones and collision zones, where large portions of plates actually can rub together as a whole, have the really big earthquakes, like the 2004 Sumatra earthquake. In other plate boundaries, the entire plate boundary does not act together, so the faults become spread out and many faults take up the strain from the tectonic stress, like with the San Andreas Fault in California (it only takes up ~3/4 of the stress between the plates).\n\nEarthquakes are really tricky things; there is still so much we need to learn. As of now, there is no way to predict them, but we can say where the danger is highest and about how long between events.
810343
Seafloor spreading did the trick.  Wegner had the drift rate up to 100 times the actual rate, because he thought that the mechanism by which the earth's plates moved was by centrifugal force and tides.  When it was discovered that the seafloor was spreading, because the underlying material would heat up and become more plastic and allow for slippage, then the mechanism was explained and the rate of drift was brought into the right range.
228826
It's because as the slab descends, it stays fairly cold (because rock doesn't conduct heat very well!), and the pressure increases.  As the pressure increases, certain minerals change their shape to more compact arrangments, typically losing water and other "volatiles" (this is called slab dehydration).  When these volatiles are lost, they move upwards into the overlying "mantle wedge", where they lower the melting point of the rock.  It's from here that magmas arise.  The reason for the 100km or so distance from the zone of subduction is due to the slab "dehydration" not occuring until a certain depth, and because the slab typically descends at an angle of ~60deg