The form of buoyancy that allows continents to float on the upper mantle is called isostasy.

Here's a breakdown:

* Isostasy is a state of equilibrium where the Earth's crust floats on the denser mantle below. It's similar to how an iceberg floats in water.

* Continental crust is less dense than the oceanic crust and the mantle. This difference in density is what allows the continents to "float" higher than the ocean floor.

* Isostatic adjustment occurs when the weight of the crust changes. For example, if a mountain range forms, the crust will sink deeper into the mantle until equilibrium is restored. Conversely, if a glacier melts, the crust will rise.

So, it's not just floating in the literal sense, but a balancing act of forces due to the different densities of the Earth's layers.