Forced convection may happen by natural means, such as when the heat of a fire causes expansion of air and bulk air flow by this means. The shock wave that transfers heat and mass out of explosions is also a type of forced convection.
Convection currents are the result of differential heating. Lighter (less dense), warm material rises while heavier (more dense) cool material sinks. It is this movement that creates circulation patterns known as convection currents in the atmosphere, in water, and in the mantle of Earth.
Mantle convection is the slow creeping motion of Earth's solid silicate mantle caused by convection currents carrying heat from the interior to the planet's surface.This subjected material sinks through the Earth's interior.
