Heat from the core and the mantle itself causes convection currents in the mantle. 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 mantle.
But What is Convection currents?
Convection current is a process that involves the transfer of energy from one place to another. Also called convective heat transfer.
Convection current is fluid flow that is moving due to temperature or density differences in a material.
Convection current is only found in gases and liquids because solid particles are stationary. The difference in temperature leads to the transfer of energy from areas of higher energy to areas of lower energy.
Convection currents Example: You can see the convection current in boiling water in a pot. Just add a few peas or a piece of paper to keep track of your current flow. The heat source at the bottom of the pot heats the water and gives it more energy, making the molecules move faster.
Changes in temperature also affect the density of water. When water rises to the surface, some of it has enough energy to escape as steam. Evaporation cools the surface and some molecules sink to the bottom of the pot.
How is Heat Transfer?
The transfer of energy from a hot body to a cold body is called heat transfer. Heat is always transferred from hot to cold. There are three types of heat transfer: radiation, conduction and convection.
The transfer of energy from empty space is called radiation. Heat transfer occurs by radiation without direct contact between the heat source and the object. For example, radiation can heat the Earth’s surface in sunlight.
Heat transfer within or between materials in contact is called conduction. In conduction, particles of heated matter transfer heat to other particles through direct contact. An example is when a spoon heats up in a hot pot of soup.
Heat transfer due to the movement of flow in a fluid is called convection. Fluids include liquids and gases. During convection, heated fluid particles begin to flow and transfer thermal energy from one part of the fluid to another.
Convective heat transfer is caused by the temperature and density difference in the fluid. Density is the amount of mass contained in a volume of a substance. When a liquid or gas is heated, the particles move faster.
As they move faster, they separate. Heated fluid particles are further apart and occupy more space. The density of the fluid decreases. However, as the liquid cools, the particles become closer together and its density increases.
An example of convection occurs when you heat a pot of soup on your stove. The soup at the bottom of the pot expands and loses its thickness when it is hot. The hotter, denser soup rises to the top and floats on top of the cooler, denser soup.
Gravity then pulls this cold, thick soup to the bottom, where it reheats and begins to rise. This flow of heat transfer in the fluid is called convection current.
Fluid heating and cooling, changes in fluid density, and gravity combine to create convection current. As long as heat is added to the fluid, convection currents continue.
Convection Currents in the Mantle
Convection currents are detected in the Earth’s mantle. The heated mantle material rises from the depths of the mantle and the cooled mantle material sinks and creates convection currents. It is believed that this type of current plays a role in the movement of the earth’s crust plates.
The heat inside the mantle is produced from the Earth’s molten outer core, the decay of radioactive elements, and the friction caused by the descending tectonic plates in the upper mantle. The heat in the outer core comes from residual energy from Earth-forming events and energy from the decay of radioactive elements.
This heat warms the base of the mantle to about 7,230°F. At the boundary of the mantle crust, the mantle temperature is estimated to be 392°F.
Heat transfer must occur due to the temperature difference between the upper and lower mantle boundaries. Conduction seems to be the more obvious method of heat transfer, but convection also occurs in the mantle. Hotter, less dense rock near the core moves slowly upward.
Relatively cool rocks from the upper mantle slowly sink into the mantle. As the hotter material rises, it cools and is eventually pushed aside by the rising hotter material and sinks towards the core.
Mantle materials such as thick asphalt or mountain glaciers flow slowly. Mantle materials remain solid, but heat and pressure cause the mantle materials to move.