COVCECTION CURRENTS

CONVECTION CURRENTS

The definition of Convection is Heat transfer through the movement of a fluid

Convection currents are caused by the very hot material at the deepest part of the mantle rising, then cooling, sinking again and then heating, rising and repeating the cycle over and over.

Convection currents occur in any fluid environment

HOW CONVECTIONS ARE MADE

Consider what happens to the water in a pot as it is heated over an open camp stove. The water at the bottom

of the pot heats up first. This causes it to expand. Since the warmed water has a lower density than the water

around it, it rises up through the cooler, dense water. At the top of the pot, the water cools, increasing its density,

which causes it to sink back down to the bottom. This up and down movement eventually heats all of the water.

The continual cycling of the fluid is called a convection current.

HOW CONVECTION CURRENTS MOVE When the convection currents flow in the mantle they

also move the crust. The crust gets a free ride with these currents. A conveyor belt in a factory moves boxess like the convection currents in the mantle moves the plates of the Earth.

The aesthenosphere (70 ~ 250 km) is part of the mantle, the middle sphere of the Earth that extends to 2900 km. It contrasts with the more rigid lithosphere, the outer shell of the Earth (0 ~ 70 km) that contains the continental crust (made up of less dense granitic rocks) and the oceanic crust (more dense basaltic rocks) that are broken up into more than a dozen rigid plates.

CONVECTION CURRENTS

Large convection currents in the asthenosphere transfer heat to the surface, where plumes of less dense magma break apart the plates at the spreading centers, creating divergent plate boundaries.

As the plates move away from the spreading centers, they cool, and the higher density basalt rocks that make up ocean crust get consumed at the ocean trenches/subduction zones. The crust is recycled back into the asthenosphere.

The collision of plates is often accompanied by earthquakes and volcanoes.

THE END