Convection current. Illustration of a convection current in water heated with a Bunsen burner flame, demonstrated by dissolving crystals of purple dye. As the water at the bottom of the beaker heats up, its density decreases. The dissolving purple dye shows the warmed water rising upward. As it moves upwards and further away from the heat source, it begins to cool. As it cools, the density increases which causes it to sink back down again. In this way a current is created that circulates the water around the beaker.