(PT) Forces that Drive Plate Movement Lesson
Forces that Drive Plate Movement
How do lithospheric plates move? What does heat have to do with the force that moves continents around? Watch the following presentation to discover the answer to these and other questions.
Watch a presentation about the Driving Forces of Plate Movement.
Plates at our planet's surface move because of the intense heat in the Earth's core that causes molten rock in the mantle layer to move. It moves in a pattern called a convection cell that forms when warm material rises, cools, and eventually sink down. As the cooled material sinks down, it is warmed and rises again.
Scientists once thought that Earth's plates just surfed on top of the mantle's giant convection cells, but now scientists believe that plates help themselves move instead of just surfing along. Just like convection cells, plates have warmer, thinner parts that are more likely to rise, and colder, denser parts that are more likely to sink.
New parts of a plate rise because they are warm and the plate is thin. As hot magma rises to the surface at spreading ridges and forms new crust, the new crust pushes the rest of a plate out of its way. This is called ridge push.
Old parts of a plate are likely to sinks down into the mantle at subduction zones because they are colder and thicker than the warm mantle material underneath them. This is called slab pull.
See description of diagram Links to an external site.
Oceanic-continental Convergence
See description of diagram Links to an external site.
As explained in the presentation, magma in the mantle is heated by the core at the center of the earth. Heated matter in the mantle expands and so, is less dense. When it rises to the surface, it pushes against the material that is there causing convection currents. The matter on the surface cools slowly and is sucked back down to replace the heated matter that has risen to the surface. The magma moves in a cyclical/circular motion. In the process, the plates on top of the mantle are slowly dragged along with it. This is why the two plates under the Atlantic Ocean are being dragged apart. No gap is ever left between the plates. As a gap begins to form, the magma from beneath pushes upwards to fill it.
See description of diagram Links to an external site.
Exploring Earth Convection
The movement of energy from a warmer object to a cooler object is called heat transfer. Heat is always transferred from a warmer substance to a cooler substance. There are three types of heat transfer: radiation, conduction, and convection.
The transfer of heat by the movement of a heated fluid is called convection. Fluids include liquids and gases. During convection, heated particles of a fluid begin to flow, transferring heat energy from one part of the fluid to another.
Heat transfer by convection is caused by differences in temperature and density within a fluid. Density is a measure of how much mass there is in a volume of a substance. When a liquid or gas is heated, the particles move faster. As they move faster, they spread apart. Because the particles of the heated fluid are farther apart, they occupy more space. The fluid's density decreases. But when a fluid cools, the particles move closer together and density increases.
Convection currents flow in the asthenosphere. The heat source for these currents is heat from Earth's core and from the mantle itself. Hot columns of mantle material rise slowly. At the top of the asthenosphere, the hot material spreads out and pushes the cooler material out of the way. This cooler material sinks back into the asthenosphere. Convection currents like these have been moving inside Earth for more than four billion years!
Demonstration: Cocoa Crust
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