Complex sentence: The driving force behind a turbidity current is the high density of the sediments temporarily suspended within it, which render the density of the turbid water as greater than the clear water through which it falls or flows.
Split into simpler sentences: The driving force behind a turbidity current is the high density of the sediments temporarily suspended within it. These semi-suspended solids tend to render the average density of the sediment bearing water as greater than that of the clear water through which it falls or flows.