What property of matter causes convection currents

This would be any movement of matter when there is a changes within the density.

The property of matter that causes convection currents is Density

Convection is heat transfer due to a density differential within a fluid. As water's temperature increases in the presence of a heat source, it will become less dense and rise. As it moves up and away from the heat source, it cools and becomes more dense and sinks.