Final answer:
The great heaps of unconsolidated sediment at the base of the continental slope are known as the continental rise. It is a region where sediments from the higher areas of the continental margin accumulate, forming distinct geologic features on the ocean floor.
Step-by-step explanation:
The great heaps of unconsolidated sediment at the base of the continental slope are known as the continental rise. This feature forms as sediment descends from the continental shelf and accumulates there, particularly during times when sea levels are low and sediments from deltas are transported in greater quantities into deep marine basins. These sediments can sometimes come in the form of turbidites, which are deposits from slope failures causing current-driven distribution of sediment sorted by density.
The continental rise often lies at the transition between the continental slope and the abyssal plains, which are exceptionally flat and deep parts of the ocean floor. The continental shelf, in contrast, is the flat and relatively shallow region extending from the shoreline to the slope. When tectonic events, such as the orogenies that formed the Appalachian/Caledonide Mountains, occur, the added weight can cause the lithosphere to bend and create basins where these sediments can accumulate.