x1 is a waterfall (geological and hydrological, semi-permanent feature) with source/flowing fluid x2 (fluid need not be water), with rock/terrain characteristics/grade (slope)/features x3 in potential (gravitational well/field) x4; mass/quantity of fluid x2 flows over feature x3 so as to fall /tumble down it (continuously)
Despite the gloss, the waterfall need not constitute falling water specifically, just a falling-tumbling fluid. x3 might be (but is not necessarily strictly) a terrain feature underlying the flow of the fluid. Proposed short rafsi: -pup-. Confer: falri'e, jacfa'u, jacfalstu.