Final answer:
Magma rises to the surface because it is lighter than surrounding rock, utilizing the same principles that allow less dense substances to float in higher-density fluids.
Step-by-step explanation:
Magma tends to rise to the surface because it is lighter than surrounding rock. The mantle beneath the Earth's crust can deform and flow slowly. While solid, it has fluid characteristics, allowing less dense materials to rise through it. This behavior is analogous to how oil floats on water or a hot-air balloon rises in the atmosphere. As the density in the mantle increases with depth, the lighter magma is buoyant and moves upward towards areas of lower density and pressure. This is similar to the principle that allows mountain ranges to 'float' on the higher-density crust and mantle below them.
Thus, magma reaches the Earth's surface because its density is less than that of the surrounding rocks deep within the Earth's mantle. This density difference is the key factor that propels magma towards the surface, where it can emerge through volcanic eruptions or form new crust material.