Convection currents move a gas or a fluid from one place to another and are created when there are differences in density or temperature within that gas or fluid. A convection current can also be thought of as a process that moves energy from one place to another. This process is sometimes referred to as convection heat transfer.
Convection currents in the air
A classic example of a convection current would be that of warm air rising towards the ceiling in a house. This happens because warm air is less dense than colder air. Wind is another example of a convection current. Wind is caused when sunlight or reflected radiation heats air, causing it to displace cooler air.
Convection currents in the ocean
Ocean currents are convection currents and are caused by differences in water density and temperature in different parts of the ocean.
Convection currents beneath the Earth's surface
Within the earth, heat that is circulating from deep below the surface melts rock to form magma. This circulating heat also causes the magma to flow, which in turn can cause the tectonic plates at the earth's surface to shift. This would be an example of very slow-moving activity caused by convection currents.