Where do convection currents form?
Convection currents occur when a fluid is near a heat source.
Heat sources provide energy to their surroundings. When fluid receives this energy, molecules inside it move around more, spacing out from each other and lowering the density.
We know from helium balloons that things with lower densities than their surroundings are pushed upwards. Therefore, the fluid close to the heat source moves upwards, as it is hotter than the rest.
As this fluid moves up, cooler molecules drift down, succumbing to gravity.
As hot molecules move up and further from the heat source, they cool down, and drop. As colder molecules drop and move towards the heat source, they heat up, and begin rising.
This results in a circular motion called a convection current. It is present in the strong winds at the seaside and in the magma in the Earth's mantle.