Melting in an impact environment can happen due to a momentary, extreme increase in P-T

Melting within the oceanic crust happens by penetrating water, so a change in 'W'

Mantle melting at oceanic hotspots is related to higher temperatures, or a change in 'T'

Decompressional melting underneath oceanic ridges is triggered through a change in 'P'

Fluxed melting in subduction zones happens through a change in 'X'