What property of matter causes convection currents

The property of matter that causes convection currents is Density

Explanation:

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.

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