Here's why:

* Lava is molten rock that has erupted onto the Earth's surface.

* Magma is molten rock that is still beneath the surface.

* Lava fields are areas where lava has flowed out onto the surface and solidified, creating a large expanse of volcanic rock.

So, while magma flows and moves beneath the surface, it's not a lava field until it erupts and flows out to form a solidified expanse.