Folds are formed when compressed rock deforms but unlike faults, it does not crack. Folding normally takes place on the boundary between two converging plates. Mountains usually start as sedimentary rock on the bottom of the sea. This is then squashed upwards by converging continental plates. It then got folded, faulted, metamorphosed, and intruded by igneous plutons.
Underwater volcanoes erupt a lot at diverging boundaries.
The water is superheated and causes melting and a volcano occurs .