Magma that solidifies in a bubble shape under the crust is called a laccolith.

Here's why:

* Laccolith comes from the Greek words "lakkos" (pit or hollow) and "lithos" (stone).

* Laccoliths form when magma intrudes into existing rock layers, but instead of pushing them upwards, it forces them to dome upwards, creating a mushroom-shaped intrusion.

* The "bubble" shape is a result of the magma's upward pressure against the overlying rock.

While the term "bubble" isn't technically correct, it's a helpful way to visualize the laccolith's shape.