What are the functions of crustal activities and tectonics and why don't they occur randomly?
148723
Basic physics determines it. It is a relief of stress and pressure in the crust.
797755
It happens in the brittle part of the crust, which is not usually deeper than 20 km.\n\nHere's the jist:\n\nIt 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.
854011
Earthquakes are the Earth's natural means of releasing stress. When the Earth's plates move against each other, stress is put on the lithosphere. When this stress is great enough, the lithosphere. \n\nAs the plates move they put forces on themselves and each other. When the force is large enough, the crust is forced to break. When the break occurs, the stress is released as energy which moves through the Earth in the form of waves, which we feel and call an earthquake. \n\nThe earth is made of around 7 major plates. These plates are part of the earths crust and are floating of top of an area of the earth known as the mantle. This is the driving mechanism for the plates. Most Earthquakes are caused by Plate Tectonics. The earth's crust consists of a number of sections or plates that float on the molten rock of the mantle. These plates move on convection currents caused by heat rising from the center of the earth. The hot magma rises and spreads out on the surface, creating new crust. The crust spreads out forming a new plate until it meets another plate. One of the plates will be pushed down into the interior of the earth and reabsorbed into the mantle. Plates can also be compressed to push up mountains when they collide or move sideways along what are known as transform faults. the other 2 faults are known as divergent faults which is when 2 paltes slowly move away from each other and converegent faults which is when 2 plates push against each other.\n\nThe plates are the Earth's crust that float on the molten rock in the center of the Earth. Most of the inside of the Earth is so hot that the rock just simply melts away. The molten rock, which is also known as magma, bubbles up very slowly in great currents under the surface of the Earth. The crust that floats on the magma moves with it. The Plates are just pieces of the crust. Just like a giant jigsaw puzzle. The part that makes it hard to understand is that it all moves extremely slowly. Just a few cm a year, roughly at the same rate a your finger nails are growing. \n\nHope this has helped you out a bit
865517
Tectonics, (from the Greek for "builder", tekton), is a field of study within geology concerned generally with the structures within the crust of the Earth (or other planets) and particularly with the forces and movements that have operated in a region to create these structures.
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
695195
Convergent boundaries occur where two plates are being pushed together and collide. This is sometimes called a "destructive plate margin". One thing to keep in mind is that when subduction occurs, the denser plate (usually the older one) generally is considered to be the one that is pushed into the hot asthenosphere. Its rocks are melted and the resulting hot magma migrate upward along cracks and weakened areas in the overriding plate forming volcanoes. Of course, you always get earthquakes along with this process. The regions where the earthquakes occur are called the Wadati-Benioff zones. However, what actually happens depend on the composition of the crustal plates involved.\n\nOceanic colliding with continental crustal plates: An example of this is the subduction of the denser oceanic Nazca Plate under the South American Plate, pushing limestone strata upward to form the towering Andes and generating destructive earthquakes. Another example is the Cascadian subduction zone off the northwest coast of the U.S. you can find volcanoes along the subduction zones. Deep trenches are formed as a result of subduction.
1016696
Volcanoes are the result of the dynamic of Earth.\nEarth's crust is broken in many blocks (tectonic plates) that are in motion respect one another. Mostly of volcanoes are located along boundaries of adjacent plates.\nVolcanic eruptions near tectonic plates' boundaries are driven by the magma that ascend from deeply beneath the crust\n\nScientific predict volcanic eruptions by studying some geophysical and geochemical parameters:\n * increasing of the seismic activity near the volcano\n * changes in the quantity of gases (CO2, SO2, etc) expelled by the volcano\n * observed changes in magnetic or geoelectrical explorations: studying the surface of the volcano with magnetic geoelectrical methods.\n\nYou can read more at links below
14315
Tectonics (and therefore earthquakes and volcanoes) is driven by the internal heat of the planet.\n\nEver since the Earth formed it has been cooling, so if anything tectonic activity is on a constant decline. The loss of heat is very slow though, so from the point of view of recorded human history there has been very little change.
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.
870655
Magma, or molten rock located beneath the earth's surface, cools upon reaching the surface to form the crust. This crust is moved away from the location of upwelling by thermal convection currents in the semi-plastic mantle. The crust is then resorbed back into the mantle upon meeting another, less dense (more buoyant) crust. \n\nThere are two types of crust: oceanic and continental. Each are made from different minerals, resulting in oceanic crust being 'heavier' (denser) and thus sinking below the 'lighter' (less dense) continental crust at convergent boundaries. The earth's crust is in a state of constant motion (or, in some places, no motion, but a building up of energy) called plate tectonics. \n\nSee the wikipedia link below for more details. Hope that helped.
210837
Tectonic movements (earthquakes), volcanic action, and erosion.  \n\n1. Tectonic movements -- As the various plates that make up the Earth's surface move around, some crash into each other and one is forced up over the other.  Thus, for example, Himalayas.  The rocks that were deep underground are forced up near the surface.\n\n2. Volcanoes spew out lava which forms igneous rocks, but certain kinds of explosions will toss out large chunks of metamorphic rock from deep underground as well.\n\n3.  Erosion is primarily responsible for most of what we see as the surface of the Earth. While the other two actions will bring the rock near the surface, the action of wind and water removes the top layers of dirt and lighter rock.  Most significant is the action of glaciers, which strip everything down to the bare rock -- this is, I believe, why you find granite near the surface in New Hampshire.
473257
Try http://www.geo.lsa.umich.edu/~crlb/COURSES/270/Lec12/Lec12.html\nIt helped me do my homework! Also, it has pictures of plate boundries and plate tectonics. Hope it helps!
421648
i think u mean tectonic plate.  tectonic plates are the sections the outer layer of earth is divided into.  there is pressure between the plates, so they sometimes slip and slide and that's how we get earthquakes.  tectonic plates are different sizes.  some only carry one island while others can have a whole continent and part of an ocean!  as for what platonic plates are, i've never heard of them, so i'm sure you mean tectonic plate.
502206
Contact - magma is injected into preexisting rock & the heat from the magma metamorphoses the rock.\n\nRegional - covers a large area; usually due to mountain forming episodes called orogenies; the mountain forming episodes are caused by two continental plates converging; neither plate subducts b/c they are both the same in density.\n\nCataclastic - occurs along faults where plates grind past each other; due to friction\n\nThere is also burial metamorphism which occurs due to great heat & pressure from burial under many layers of sediment; when heat & pressure becomes great enough, burial metamorphism becomes regional.
696568
They are results of the centrifugal and centripetal forces of the earth crust. This results faulting and folding of the earth's surface.
731013
Really, the answer to your question is simply: Plate Tectonics. Read below for details.\n\nEarthquakes: \nIt all comes down to stress and strain from the interaction of different plates, chiefly at the boundaries. 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.\n\nVolcanoes:\nThere 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\nMountain Belts:\n\nNon-volcanic mountain belts are caused by compressive stress in plate tectonics. This can be 1. fold and thrust belts in highly compressive subduction zones (almost always from oceanic beneath continental subduction, e.g. east Andes, Rockies) or 2. continental-continental collisions (e.g. Himalaya, Appalachian).
905919
An earthquake is a phenomenon that results from and is powered by the sudden release of stored energy in the crust that propagates seismic waves. At the Earth's surface, earthquakes may manifest themselves by a shaking or displacement of the ground and sometimes tsunamis, which may lead to loss of life and destruction of property.\n\nEarthquakes may occur naturally or as a result of human activities. In its most generic sense, the word earthquake is used to describe any seismic event—whether a natural phenomenon or an event caused by humans—that generates seismic waves.\n\nTypes of earthquakes\n\nNaturally occurring earthquakes :-\nMost naturally occurring earthquakes are related to the tectonic nature of the Earth. Such earthquakes are called tectonic earthquakes. The Earth's lithosphere is a patchwork of plates in slow but constant motion caused by the heat in the Earth's mantle and core. Plate boundaries grind past each other, creating frictional stress. When the frictional stress exceeds a critical value, called local strength, a sudden failure occurs. The boundary of tectonic plates along which failure occurs is called the fault plane. When the failure at the fault plane results in a violent displacement of the Earth's crust, the elastic strain energy is released and seismic waves are radiated, thus causing an earthquake. This processes of strain, stress, and failure is referred to as the Elastic-rebound theory. It is estimated that only 10 percent or less of an earthquake's total energy is radiated as seismic energy. Most of the earthquake's energy is used to power the earthquake fracture growth and is converted into heat. Therefore, earthquakes lower the Earth's available potential energy, though these losses are negligible\nEarthquakes occurring at boundaries of tectonic plates are called interplate earthquakes, while the less frequent events that occur in the interior of the lithospheric plates are called intraplate earthquakes.\n\nThe majority of tectonic earthquakes originate at depths not exceeding a few tens of kilometers. In subduction zones, where older and colder oceanic crust descends beneath another tectonic plate, earthquakes may occur at much greater depths (up to hundreds of kilometers). These seismically active areas of subduction are known as Wadati-Benioff zones. Deep focus earthquakes are another phenomenon associated with a subducting slab. These are earthquakes that occur at a depth at which the subducted lithosphere should no longer be brittle, due to the high temperature and pressure. A possible mechanism for the generation of deep focus earthquakes is faulting caused by olivine undergoing a phase transition into a spinel structure.\nEarthquakes may also occur in volcanic regions and are caused by the movement of magma in volcanoes. Such quakes can be an early warning of volcanic eruptions.\n\nA recently proposed theory suggests that some earthquakes may occur in a sort of earthquake storm, where one earthquake will trigger a series of earthquakes each triggered by the previous shifts on the fault lines, similar to aftershocks, but occurring years later, and with some of the later earthquakes as damaging as the early ones. Such a pattern was observed in the sequence of about a dozen earthquakes that struck the North Anatolian Fault in Turkey in the 20th Century, the half dozen large earthquakes in New Madrid in 1811-1812, and has been inferred for older anomalous clusters of large earthquakes in the Middle East and in the Mojave Desert.\n\n\nInduced earthquakes :- \n\nSome earthquakes have anthropogenic sources, such as extraction of minerals and fossil fuel from the Earth's crust, the removal or injection of fluids into the crust, reservoir-induced seismicity, massive explosions, and collapse of large buildings. Seismic events caused by human activity are referred to by the term induced seismicity. They however are not strictly earthquakes and usually show a dif