Ocean floor research papers reveal that the ocean floor is characterized by a series of four recognizable topographic features. While the size of each of these features varies within the various ocean basins, they are always present.
Layers of the Ocean Floor
The four features of the ocean floor are as follows:
- Continental Shelf
- Continental Slope
- Continental Rise
- Abyssal Plain
Continental Shelf - The continental shelf is the gently sloping platform at the edge of the continent. The shelf is generally thought to be an extension of the continent and not really a part of the ocean basin. The average water depth on the shelf is about 75 meters, varying from zero at the shoreline to about 150 meters near its edge. A typical continental shelf is 60 kilometers wide, but it exceeds 100 kilometers off the Florida coast and is less than a few kilometers wide in places along the West Coast of South America. The rock underlying the thin veneer of sediments is granite similar to the basement rock elsewhere beneath the continents.
Continental Slope - The continental slope marks the transition between the continental shelf and deep ocean floor. It has an average slope of 3-6 degrees, which may not sound like much, but means that over a distance of 100 kilometers, water depth increases from 75 meters to 4000 meters. Typically, continental slopes are crisscrossed by a series of deep submarine canyons the origin of which is not entirely known and remains a Ocean Floor of some controversy within oceanographic circles. Some of these canyons represent drowned stream valleys, but others were clearly never above sea level and can not have been cut downward by stream erosion.
Continental Rise - The continental rise represents the accumulation of sediment at the base of the continental slope. The result of this accumulation is a gentler slope and the buildup of streaming or, "turbidite" deposits. Uplifted turbidite deposits are common along the coastline of southern California, particularly at Blacks and Torrey Pines beaches north of San Diego. Southern California turbidites are thought to form during major earthquakes which cause sediments to slide off the edge of the shelf and accumulate on the ocean floor as "fining upward" sequences of sedimentary rocks. "Fining upward" is a term characterizing rocks or particles that get smaller at the top.
Abyssal Plain - The abyssal plain is basically the ocean floor, and covers about 30% of the earth's surface. The average water depth is around 5000 meters. The abyssal plain consists of a layer of unconsolidated sediment underlain by sedimentary rock and pillow basalt - a dark fine-grained variety of volcanic rock.