What are the different types of plate tectonic boundaries?
1. Divergent Boundary: A divergent boundary occurs when two tectonic plates move away from each other. Along these boundaries, lava spews from long fissures and geysers spurt superheated water. Frequent earthquakes strike along the rift. Beneath the rift, magma—molten rock—rises from the mantle. It oozes up into the gap and hardens into solid rock, forming new crust on the torn edges of the plates. Magma from the mantle solidifies into basalt, a dark, dense rock that underlies the ocean floor. Thus at divergent boundaries, oceanic crust, made of basalt, is created.2. Convergent Boundary : When two plates come together, it is known as a convergent boundary. The impact of the two colliding plates buckles the edge of one or both plates up into a rugged mountain range, and sometimes bends the other down into a deep seafloor trench. A chain of volcanoes often forms parallel to the boundary, to the mountain range, and to the trench. Powerful earthquakes shake a wide area on both sides of the boundary. If one of the colliding plates is topped with oceanic crust, it is forced down into the mantle where it begins to melt. Magma rises into and through the other plate, solidifying into new crust. Magma formed from melting plates solidifies into granite, a light colored, low-density rock that makes up the continents. Thus at convergent boundaries, continental crust, made of granite, is created, and oceanic crust is destroyed.3. Transform plate boundary : Two plates sliding past each other forms a transform plate boundary. Natural or human-made structures that cross a transform boundary are offset—split into pieces and carried in opposite directions. Rocks that line the boundary are pulverized as the plates grind along, creating a linear fault valley or undersea canyon. As the plates alternately jam and jump against each other, earthquakes rattle through a wide boundary zone. In contrast to convergent and divergent boundaries, no magma is formed. Thus, crust is cracked and broken at transform margins, but is not created or destroyed.
Why do most volcanoes and earthquakes occur at plate boundaries?
Because plate boundaries are where two tectonic plates are colliding in some way. Sometimes one plate is sliding under another and sometimes the plates are colliding head on.Oceanic plates usually slide under continental plates. As they do so, seawater is taken with them deep into the mantle. As the water is heated up it can cause some of the underside of the overlapping plate to melt. Since this molten rock is lighter than solid rock, it rises to the surface in the same way globs in a lava lamp rise toward the top of the lamp as they get warm. When this magma reaches the surface of the Earth, a volcano is formed.As for increased numbers of earthquakes at plate boundaries, this is in part due to volcanic activity but mostly its due to the collision of the plates. Plate collisions are an extremely slow process, each plate moving about an inch per year. Sometimes one plate gets stuck as it is sliding under the other. Pressure builds up until suddenly the plate moves up to several feet at once. A plate moving that far at once is the equivalent of how far it would have moved normally over the course of thousands of years. Thus a lot of energy released in the form of large earthquakes. Very small earthquakes happen almost constantly at plate boundaries due to the usual movement of the plates against each other.
Why are most of the volcanoes found on the plate boundaries?
There are three major volcanic settings:Divergent plate boundariesConvergent plate boundariesHot SpotsDivergent Plate Boundaries. Iceland is the best example. Magma beneath the diverging plates normally rises and fills cracks between the plates. If divergence is rapid, it may reach the surface and erupt. Since it comes from the mantle with little modification, it’s mostly basalt.When the spreading is slow, and under a continent, often the magma incorporates odd ingredients that have accumulated beneath the crust. You can get some very weird composition lavas like the sodium carbonate at Ol Doinyo Lengai.Convergent Plate Boundaries (Subduction Zones). Generally there’s a descending slab of oceanic crust, and it’s been soaking in sea water for a long time. As it descends and heats up, it gives off water that lowers the melting point of the adjacent rocks. Magma rises and may erupt.If the overriding plate is also oceanic crust, then you have a basaltic plate intruding a basaltic plate, and the resulting volcanoes erupt basalt, like the Marianas and other South Pacific island chains.If the overriding plate is continental, the initial volcanic eruptions produce basalt, but as time goes on, the magma reacts with the continental crust and becomes richer in silica. The volcanoes erupt andesite and later on, rhyolite.Hot Spots. These are long-lasting plumes of rising hot rock that melt near the surface. If they’re located under an oceanic plate, like Hawaii, they produce - now let’s not always see the same hands - basalt.If they occur under continents, then again the magma reacts with the continental crust and becomes more silica rich, like Yellowstone.
What geological events occur at plate boundaries?
Excellent answer given.Transform Plate BoundaryI grew up near one of the most famous plate boundaries in the world, a transform boundary, which separates the Pacific plate from the North American plate. We have experienced, since I was born, over 1,320,000 earthquakes (all sizes, mostly small quakes) that have occurred in and around this plate boundary - one of the most seismically active areas of the world (and a great place to study geology, seismology, vulcanology, plate tectonics, geomorphology, petrology, paleontology, mineralogy, geophysics, and so many more disciplines).Convergent Plate BoundaryConvergent plate boundaries, such as the Indian plate and Eurasian plate boundary, have produced (and are still producing) the Himalayas and the uplifted Tibetan plateau; other convergent plate boundaries, between continental plates (Eurasian, North American, and South American) and oceanic plates (Pacific and other minor plates, such as the Juan de Fuca, the Cocos, the Philippine Sea plates) causes the oceanic plates to dive under the continental plate, giving many deep quakes, tsunamis, volcanic arcs (e.g. the infamous Ring of Fire, which consists of 452 volcanos, active and dormant). Subduction rates vary greatly, depending on the speed of encroachment of the overriding plate, the speed of the nearest seafloor spreading zone, and so forth.Divergent Plate BoundaryA divergent plate boundary is essentially the seam between plates (oceanic or continental) where new magma / lava is introduced and where the plates that are either side of that seam are augmented. Rates of spreading varies, from 3 cm/yr at the Mid-Atlantic Ridge to 14 cm/yr at the East Pacific Rise (spreading rates at the EPR were as high as 20 cm/yr). The Rift Valley of East Africa is another spreading zone, which is slowly ripping Africa into two sections, moving at between 6–7 mm/yr.Map courtesy of WikimediaIn an estimated 10 million years, the lithosphere will rupture, the Somalian plate will break off, and a new ocean basin will form.The interplay of the various types of Plate boundaries gives us the surface features that we have come to know. In a slow dance, the surface is always changing, with some plate boundaries building up, others tearing down, and others still grinding away.[1]Footnotes[1] East African Rift - Wikipedia
What happens when an oceanic plate collides with a continental plate, and when two continental plates collide?
Typically, when an oceanic and a continental plate collide, the oceanic plate buckles and begins to subside beneath the continental plate (which is less dense, and thicker). The continental plate above the descending oceanic plate, usually begins to feel the effects of the collision in the form of compressive tectonism - which create folds, faults (and earthquakes) and volcanoes may (and usually do) form, while coastal mountain ranges also are formed due to the compression associated with the collision. Depending on exactly where the subducting oceanic plate is, the volcanic activity will be andesitic and on land (Andes) or will be more basaltic and form a new island chain (Japan).When two continental plates collide, either of two things happens: one plate begins to subduct below the other, with similar overall effects to the overriding plate, OR both plates buckle up and being to rise (the Himalayas are the product of the collision of two continental plates).
Why are there no volcanoes in Wisconsin?
Wisconsin is not near or on any convergent or divergent boundaries (It's within the North American Plate) and it isn't over a hot spot, so there is nothing to create volcanoes.