If the plates suddenly stopped moving and no new crust was created, the whole world would become one gigantic ocean, as the continental crust would get eroded down to below sea level. Plate boundaries are crucial, as they are where new land is created. Oceanic crust gets thicker and colder the further away it is from a mid-ocean ridge. Oceanic plates are thinner, denser and made of basaltic rock, while the continental plates are thicker, less dense and made of granitic rock. The Earth’s topmost layer, called the crust, is broken up into pieces called tectonic plates. Red arrows indicate the direction of plate movement. These rocks become the source of many of our largest mineral deposits. Plate boundaries are also a way for deep-seated rocks from the mantle to find a way to the near-surface. The energy released along a plate boundary results in volcanic and hydrothermal activity that creates the right conditions for mineral concentration. It also explains why the Himalayas are the highest mountains in the world while the highest peak in Australia is barely over 2000m! Plate tectonics is the theory that explains why there are lots of volcanoes in Iceland and Japan, but far fewer in Russia and Africa. The physics is simple: something’s gotta give, and there are probably going to be fireworks – or at least volcanic eruptions and earthquakes! But along with the destruction comes the creation of many of the mineral deposits we rely on to support modern life. The most unstable areas of all are the plate boundaries, where giant crustal plates collide. The earth that we stand on, and think of as fixed, is anything but. Let knowledge be the cure.The world is a dynamic place. Powered by django-wiki, an open source application under the GPLv3 license. Transform boundaries are very common around mid-ocean ridges, but also occur in continental crust. This action often causes shallow earthquakes. In this process, the crust is fractured and deformed, but it is not destroyed (as it is in convergent boundaries) or created (as it is in divergent boundaries). Two plates moving horizontally past each other form a transform fault. Oceanic-continental divergent boundaries don't usually occur in nature, as there is unlikely to be a force that pulls apart oceanic and continental crust exactly at their boundary. This is where seafloor spreading takes place and new oceanic crust is formed. Oceanic-oceanic divergent boundary: When two oceanic plates diverge, magma rises through the rift valley, creating mid-ocean ridges that appear like volcanic mountain ranges on the ocean floor. Rift valleys form, resembling a narrow area of lowland with highland on either side. As the continental plates converge mountain ranges are formed.ĭivergent boundaries occur when two plates move away from each other (diverge), creating a long, narrow depression called a rift valley.Ĭontinental-continental divergent boundary: In most cases, diverging continental plates are found where a continental plate begins to break apart. The only exception is if ancient oceanic crust is still attached to the continental crust, then the oceanic crust will be subducted. Deep earthquakes can form in the subduction zone.Ĭontinental-continental convergent boundary: When both converging plates are continental neither is subducted, as continental crust is buoyant in the mantle. A trench forms on the ocean floor at the subduction zone, and a volcanic arc (a volcanic mountain range) forms on the continental plate parallel to the trench. This is because oceanic crust is much denser than continental crust. Oceanic-continental convergent boundary: When a continental and an oceanic plate converge, the oceanic plate is always subducted. Deep earthquakes can form at the subduction zone. On the overriding plate, a volcanic island arc (a chain of off-shore volcanoes) forms parallel to the trench. Oceanic-oceanic convergent boundary: Converging oceanic plates form trenches in the subduction zone, the point where the denser plate is subducted. While the motion of the plates is the same, the resulting landforms can be very different depending on the type of plates involved. Convergent BoundaryĬonvergent boundaries occur when two plates move towards each other (converge). At each boundary, the resulting landforms depend on whether the plates involved are oceanic, continental, or both types.įigure 1: The three categories of plate boundaries: convergent, divergent, and transform. There are three categories of plate boundaries: convergent, divergent, and transform.
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