Explain why volanoes form at both convergent plate boundaries and divergent plate boundaries?
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.
85175
There's no such thing as a volcanic plate.\n\nTechtonic plates "float" on the earth's mantle, and most of the earths volcanism occurs where those plates meet.  The motion of these plates is mostly driven by convection currents in the mantle and is beyond the scope of this post.
1128821
tectonic plates are giant pieces of the Earth's crust.  They "float" on the mantle, a layer of liquid rock under the crust.  The plates are constantly moving.  A mountain range is formed when two plates moving toward each other collide.  One plate will "run over" the other.  When this happens the top plate gets pushed up and the bottom pushed into the mantle.  The top plate will rise to form a mountain range.\n\nClimate and erosion give the mountain range its finished look (paint on the car).  The tectonic movement gives it its general shape.
363137
I think Stillkelsie and GruHairy have the best answers.  \n\nIf one (or both) of the colliding plates are oceanic plates (thinner and a bit denser), one will slide underneath the other and be pushed down.  You'll typically get a subsea trench where the two plates meet, such as the Marianas Trench in the western Pacific Ocean.  After the sliding's gone on long enough, some of the "pushed-down" plate will melt, and the lighter melted rock will try to rise to the surface, where it can form volcanoes or cool underground as granites and such.\n\nIf two continental plates (thinner and less dense than oceanic plates) collide, they'll tend to mash each other and "pile up".  The Himalaya Mountains, earth's tallest, were formed when the Indian continental plate collided with Asia.\n\nYou get earthquakes associated with both types of collisions.
882302
Basicaly, the plates are floating apart forming a gap between them.  This gap, or fissure is where basaltic(normally) magma spurts of of the Earth.  Fissures can be long and narrow but not very explosive.\n\nPeace
894274
The idea of Continental Drift was the forerunner of Plate Tectonics Theory. At the time that Wegener proposed the idea of Continental Drift, he did not have sufficient information to explain the physical mechanisms that would have allowed continents to break apart and drift apart. He did have fossil evidence, and shape-of-the continents evidence, and matching-rocks-on-both-sides evidence that the continents had indeed been juxtaposed. "A fatal weakness in Wegener's theory was that it could not satisfactorily answer the most fundamental question raised by his critics: What kind of forces could be strong enough to move such large masses of solid rock over such great distances? Wegener suggested that the continents simply plowed through the ocean floor, but Harold Jeffreys, a noted English geophysicist, argued correctly that it was physically impossible for a large mass of solid rock to plow through the ocean floor without breaking up."http://pubs.usgs.gov/gip/dynamic/historical.html\n\nLater, when scientists discovered magnetic striped on the ocean floor, learned more about the seismicity at trenches, and so forth, they were able to put together a more comprehensive model of the actual physical processes that could and do cause the continents to "drift" apart, or collide together. These processes come under the heading of Plate Tectonics--which includes the ideas of three types of plate boundaries, including the divergent boundaries with spreading ridges required for continents to "drift" apart. \n\n"From seismic and other geophysical evidence and laboratory experiments, scientists generally agree with Harry Hess' theory that the plate-driving force is the slow movement of hot, softened mantle that lies below the rigid plates. This idea was first considered in the 1930s by Arthur Holmes, the English geologist who later influenced Harry Hess' thinking about seafloor spreading. Holmes speculated that the circular motion of the mantle carried the continents along in much the same way as a conveyor belt. However, at the time that Wegener proposed his theory of continental drift, most scientists still believed the Earth was a solid, motionless body. We now know better. As J. Tuzo Wilson eloquently stated in 1968, "The earth, instead of appearing as an inert statue, is a living, mobile thing." Both the Earth's surface and its interior are in motion. Below the lithospheric plates, at some depth the mantle is partially molten and can flow, albeit slowly, in response to steady forces applied for long periods of time. Just as a solid metal like steel, when exposed to heat and pressure, can be softened and take different shapes, so too can solid rock in the mantle when subjected to heat and pressure in the Earth's interior over millions of years."http://pubs.usgs.gov/gip/dynamic/unanswered.html\nThe website below will give you illustrations and discusses both continental drift and plate tectonics.
841947
A mid ocean ridge is an area where new sea floor is created throught the divergent (speading) motion of the tectonmic plates in that area. At mid ocean ridges, fractures from the pulling allow small amounts of magma to squeeze in and push the plates that much more.\n\nIt comes down to density. The center of the ridge is high, because it it new (just formed) and hot. The edges are low because it is old and cold. There are two main theories on the cause: slab pull and ridge push.\n\nRidge push is the classic idea that the ridge is a high point of a convection current, pushing the plates aside and allowing new mantle material to rise up and fill the hole.\n\nSlab pull is the new idea that the subducting end of the plate, that is really old and dense, pulls on the entire plate as it subducts, and thus pulls apart itself in places, causing a hole which is then filled by rising material, forming the ridge.\n\nIt's kinda a chicken/egg thing, so we may never be able to rule one or the other out.
897089
Well believe it or not it is the composition of the two. \ncontinental crust is "typically" silicic, meaning it is composed largely of silica rich minerals, oceanic crust is more commonly "mafic" meaning it is composed of minerals with abundant Iron and Magnesium.  This oceanic crust is heavier.\nBecause of this the continental crusts are "floating" higher than the oceanic crusts.  When the two converge (i.e. along the west coast of south america for example) typically the lower oceanic crust is subducted beneath the continental crust..\nCool huh
207440
Types of plate movement:\nlateral (ie., San Andreas fault in CA) - side by side\nconvergent (ie.,Himalayan Mts.) - pushing together\ndivergent (ie., mid Atlantic Ridge) - pulling apart.\nCheck this site:\n\nhttp://www.northstar.k12.ak.us/schools/joy/denali/DAuria/plate_mvmt.html
836192
The Earth is formed of several layers that have very different physical and chemical properties. The outer layer, which averages about 70 kilometers in thickness, consists of about a dozen large, irregularly shaped plates that slide over, under and past each other on top of the partly molten inner layer. Most earthquakes occur at the boundaries where the plates meet. In fact, the locations of earthquakes and the kinds of ruptures they produce help scientists define the plate boundaries. \nThere are three types of plate boundaries: spreading zones, transform faults, and subduction zones. At spreading zones, molten rock rises, pushing two plates apart and adding new material at their edges. Most spreading zones are found in oceans; for example, the North American and Eurasian plates are spreading apart along the mid-Atlantic ridge. Spreading zones usually have earthquakes at shallow depths (within 30 kilometers of the surface).  \n\nTransform faults are found where plates slide past one another. An example of a transform-fault plate boundary is the San Andreas fault, along the coast of California and northwestern Mexico. Earthquakes at transform faults tend to occur at shallow depths and form fairly straight linear patterns. \n\nSubduction zones are found where one plate overrides, or subducts, another, pushing it downward into the mantle where it melts. An example of a subduction-zone plate boundary is found along the northwest coast of the United States, western Canada, and southern Alaska and the Aleutian Islands. Subduction zones are characterized by deep-ocean trenches, shallow to deep earthquakes, and mountain ranges containing active volcanoes.\n\nEarthquakes can also occur within plates, although plate-boundary earthquakes are much more common. Less than 10 percent of all earthquakes occur within plate interiors. As plates continue to move and plate boundaries change over geologic time, weakened boundary regions become part of the interiors of the plates. These zones of weakness within the continents can cause earthquakes in response to stresses that originate at the edges of the plate or in the deeper crust. The New Madrid earthquakes of 1811-1812 and the 1886 Charleston earthquake occurred within the North American plate.
933188
The idea of Continental Drift was the forerunner of Plate Tectonics Theory. At the time that Wegener proposed the idea of Continental Drift, he did not have sufficient information to explain the physical mechanisms that would have allowed continents to break apart and drift apart. He did have fossil evidence, and shape-of-the continents evidence, and matching-rocks-on-both-sides evidence that the continents had indeed been juxtaposed. "A fatal weakness in Wegener's theory was that it could not satisfactorily answer the most fundamental question raised by his critics: What kind of forces could be strong enough to move such large masses of solid rock over such great distances? Wegener suggested that the continents simply plowed through the ocean floor, but Harold Jeffreys, a noted English geophysicist, argued correctly that it was physically impossible for a large mass of solid rock to plow through the ocean floor without breaking up."http://pubs.usgs.gov/gip/dynamic/historical.html\n\nLater, when scientists discovered magnetic striped on the ocean floor, learned more about the seismicity at trenches, and so forth, they were able to put together a more comprehensive model of the actual physical processes that could and do cause the continents to "drift" apart, or collide together. These processes come under the heading of Plate Tectonics--which includes the ideas of three types of plate boundaries, including the divergent boundaries with spreading ridges required for continents to "drift" apart. \nThe website below will give you illustrations and discusses both continental drift and plate tectonics.
192697
It is directly related only to earthquakes.  When a plate boundary ruptures, an earthquake occurs.\n\nIt is indrectly related to volcanism.  Most volcanoes are located on plate boundaries.
794138
The continental plates do not actually 'drift' as you may think of an ice cube 'drifting' in water. Nor are the plates all connected together like one would view a jigsaw puzzle.\n\nThe first idea you have to realize is that the continental plates overlap each other. The 'outlines' you see that appear jigsaw-like are more often than not areas where two plates meet, and one plate is actually going under  the one next to it- this is called 'subduction'.\n\nWhich plate goes under which plate depends on the age and weight of the plates-- continental crust is lighter than oceanic plate, so more often than not it is the oceanic piece of the plate that will 'subduct'.\n\nThere are areas, however, where the plates do actually meet like a jigsaw puzzle-- these places are known as "Strike-slip" faults, where two plates slide past each other rather than 'subducting'.\n\nAs for the plates moving, that happens due to the upper mantle (the liquid part under the crust) creating convective currents-- these 'currents of mantle material' cause the plates to move and subduct (or slide past each other!)\n\nAnd yes, there are plates where continental crust and continental crust meet. What happens then? More often than not, mountains form-- The Himalayas are a prime example of this situation (the Indian plate smashed into the Asian plate).\n\nThere's more to it, but I hope this helps a little bit!
198939
Not really, there is no convergent plate margin near there.  If there's no subduction, mantle hot-spot, and no rift zone, there should be no volcanism.  Iceland, on the other hand, sits right on the mid-atlantic ridge AND over a mantle hot spot, so it's active like crazy.
846532
There are several processes in Plate Tectonics that cause volcanism, but they result in two main types of volcanism.\n\nVolcanism in subduction is caused by volitals, like H2O, CO2. These are carried down by the plate, mainly in the form of weak minerals. These minerals break down with pressure and temperature into stronger minerals that don't contain water and carbon dioxide. The leftover gases and liquids travel into the mantle (the mantle wedge) and hydrate the mantle, causing melting. The melt rises and then... volcano!\n\nThe other main cause is from rising mantle material, which forms decompression melting. Basically, hot mantle is kept from melting by the pressure of the earth at depth. When this material rises, the pressure drops much faster than the temperature, and thus it partially melts. This mainly occurs at divergent boundaries and hot spots, which are areas in plate tectonics that have rising materials or spreading.\n\nBy the way, as far as scientists know, the largest ever was the 27.8 Ma eruption of the Fish Canyon Tuff at La Garita in Colorado, estimated at 3,000 - 5,000 cubic km.\n\nTambora in 1815 was the largest in recorded history, 100 cubic km.
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.
475416
Nope; the oceanic plates are spreading apart, as new material (magma) is pushed up from below.  They are not crashing together at all.