If it can't happen, it didn't happen. Seismologists developed the ability to accurately locate the focus of an earthquake, and to map the foci of a large number of earthquakes worldwide. Geological oceanography developed rapidly in response to U-boat and other maritime threats during the two World Wars. Magnetometers developed by Lord Blackett, as a byproduct of the effort to detect German magnetic mines along the east coast of England, were able to measure the faint magnetic fields in rocks, permitting the development of the field of geomagnetics. For example, the North American Plate extends from approximately the San Andreas Fault in California eastward to the crest of the Mid-Atlantic Ridge.
Diapirs are common where a more dense fluid exists above a less dense fluid.
The less dense fluid may collect in a sufficient volume that its buoyancy is able to overcome the resisting forces of the overlying fluid's viscosity. The less dense fluid will then rise into the more dense fluid, seeking an equilibrium position within or above the more dense fluid. In Earth's mantle, the hotter mantle material is less dense than cooler mantle material of the same composition, so mantle diapirism is driven by heat and gravity. As the lithosphere moves over a mantle plume, the heat of the plume causes partial melting in the lithosphere. Magma rises to the surface to form volcanoes.