Final answer:
Submarine canyons on the continental slope are believed to have been created by tectonic cracks and shaped by erosion, primarily wind. Thus, the correct option is 4) none of these
Step-by-step explanation:
The submarine canyons found on the continental slope are believed to have been created by tectonic cracks rather than by rivers during the ice age or faulting. These canyons are formed by the same crustal tensions that caused uplift in other areas. Although water has played a role in shaping the canyons through erosion, the primary form of erosion in the canyons today is wind. Submarine canyons found on the continental slope are believed to have been created by various processes, and the most commonly associated process is erosion.
However, none of the options provided (1) rivers during the ice age, (2) faulting, or (3) a plate plunging into the mantle directly address the primary mechanism behind the formation of submarine canyons. Therefore, the answer would be (4) none of these, as erosion by turbidity currents, underwater landslides, or other sedimentary processes are typically responsible for creating submarine canyons.