The crust we sit on seems like one piece, but it's really made of huge plates that float on the hot liquid mantle. Some of the plates slide sideways past each other without a fuss. But deep under the ocean, plates pull apart from each other and hot magma rises from inside the earth to fill the crack. And things get really dramatic when an ocean plate crashes and rubs against a continental plate. Continents sit on plates made of thick, but light, crust.
Oceans sit on thinner, heavier crust.
Heavy things like you guys sink. The ocean plate is forced down and under. As it slides, it starts to melt. Melted rock pushes slowly up through the crust. Rocky felt his crystals crackle with excitement.