Answer:
Rocks become less dense when they melt.
Explanation:
Magma tends to rise toward Earth's surface principally because rocks become less dense when they melt. When the Earth's crust becomes very hot the rocks are molten or semi-molten. As they are less dense when they melt they tend to move upwards to the surface. The melting of the rocks is a slow process due to the minerals that form the rocks which have different compositions.