what are 3 types of interactions that occur around plate boundaries? Need asnwer Asap pleasse
Chosen Answer:
(1) Divergent boundaries — This occurs where two plates are moving apart, due to seafloor spreading. Seafloor spreading is caused by magma being brought to the surface by the enormous mantle convection cells. The magma rises between the two semi-separate plates, and wedges its way between them. Just like any wedge, it pushes the plates apart by a tiny bit. Thousands and thousands of tiny bits of wedging create spreading. The primary divergent boundary is the Mid-Ocean Ridge, which winds around every ocean basin in the world. There are different spreading rates depending on where you are. At the northern end of the Mid-Atlantic Ridge, North America and Eurasia are spreading at about 2.4 cm per year (about the rate at which the average human fingernail grows in a year). But at the East Pacific Rise/Ridge, the plates are moving apart at nearly 9 cm per year. New crust is created at divergent boundaries.
(2) Transform boundaries (sometimes called conservative boundaries) — This occurs when two plates grind past each other without the creation or destruction of crust material. They just skitter along, building up stress, because rocks are being pressed together enough that they “lock” along the faults. When these fault-faces finally take in more energy than they can handle, the rock snaps in what is called “elastic rebound” which creates an earthquake. At transform boundaries, these earthquakes are semi-large and semi-shallow, and fairly frequent. All of this poses a fairly significant threat to civilization, if our buildings haven’t been built to good codes (for instance, compare Port-au-Prince, Haiti, with San Diego and Los Angeles — much different affect for the same energy earthquake). Obviously, the most famous example of a transform boundary is the San Andreas Fault Zone, where the Pacific plate is moving north relative to the North American plate, moving south. Note that it’s a *zone* not a “fault.” There no one single fault, it’s a huge network of interconnected faults. The Haiti earthquake, as mentioned, was created along another transform fault, the Enriquillo-Plantain Garden fault system, where the Caribbean plate is moving east, against the North American plate moving west.
(3) Convergent boundaries — This is where plates/crust come together. But it’s not quite so simple. There are three sub-types of convergent boundary, based on the types of crust involved —>
Continental-continental — Where two pieces of continental crust come together. They are equally buoyant (or close enough), so the best that they can do is slam together like a head-on collision between two buses. Each plate wants to put its rock in the exact same place that the other plate wants to put its rock. Obviously, one location can be occupied by only one piece of matter at one time. So these huge, solid continental rocks end up squirting out to the sides and up to the sky. This is incredibly seismic, with huge and devastating earthquakes, better or worse depending on exactly where you are. So, where might you be? The Himalayas were created, and continue to be created, by the convergence of the northern-moving Indo-Australian plate and the more southerly-moving Eurasian plate. The European Alps are a similar issue, African plate versus Eurasian plate. Continental-continental collisions are *not* volcanic.
Oceanic-oceanic — As you may guess, when two pieces of oceanic crust come together. Very interesting things happen. First, they will decide who is cooler and denser (which will always be the older plate). Second, the denser plate will dive below the slightly-more-buoyant plate, in what is called subduction. The more buoyant plate will continue to push over the subducting plate. It is at this type of boundary, called a subduction boundary, where crust is destroyed (remember, created back at the divergent boundary). The subducting plate gets so deep into the mantle that the heat completely melts the plate. It’s just gone. This new magma is hot, and more buoyant than the surrounding rock, so it rises like a very slow balloon, and eventually pops out the surface… deep underwater. Now, you give it thousands of years, and thousands of lava flows, and you end up with a long volcanic island arc, as the volcanic islands pop out of the ocean. Note that it’s a whole line of islands, not just one, because the subduction is acting along a plane. Excellent examples of volcanic island arcs are the Aleutians, where the Pacific plate is subducting beneath the North American plate, and the Marianas Islands, where the Pacific plate is subducting beneath the Philippine plate. Notice that all of the volcanoes will erupt on the side of the more buoyant, overriding plate.
Oceanic-continental — Very similar to the oceanic-oceanic, save for two details. First, the continental crust will *always* be the more buoyant. I just ran out of room.
by: Earth Man
on: 4th June 10