Continental margin
Outer edge of continental crust under coastal waters.
The continental margin is the submerged transition zone where continental crust meets oceanic crust. It is one of the three main divisions of the ocean floor, alongside deep-ocean basins and mid-ocean ridges, and covers roughly 28% of the ocean's area. This margin is made up of three distinct parts: the continental shelf, the continental slope, and the continental rise.
The continental shelf is the shallow, flat area extending from the shoreline out into the ocean. It makes up about 7% of the seafloor, and its width varies widely, from just 30 meters to 1,500 kilometers. The shelf has a very gentle average slope of just 0° 07′, though it is typically steeper near the coast and flattens out toward the shelf break. At the shelf break, the seafloor angle increases sharply, marking the start of the continental slope. This slope can rise 1 to 5 kilometers above the deep-ocean floor. It is often carved by V-shaped submarine canyons with near-vertical sides, which sometimes cut back into the continental shelf and continue down to the abyssal plain. At the base of the slope, the angle decreases suddenly, and the seafloor begins to level out. This final zone is the continental rise, the outermost part of the margin.
There are two types of continental margins: active and passive. Active margins are found at lithospheric plate boundaries, where tectonic activity—such as volcanoes and earthquakes—is common. They can be convergent or transform. Convergent active margins, the most common type, occur where an oceanic plate subducts beneath a continental plate. Transform active margins are rarer, with plates sliding past each other in opposite directions, creating offshore faults and a rugged landscape of islands, shallow banks, and deep basins known as a continental borderland. Active margins are typically narrow, with a steep drop from the coast to the shelf break and often into deep trenches. Examples include the west coasts of North and South America.
Passive margins, in contrast, lie within lithospheric plates, far from plate boundaries, and experience little tectonic activity. They often face mid-ocean ridges and are characterized by wide, gently sloping shelves, long river systems, and thick sediment piles. The east coast of the United States is a passive margin. These margins are much wider and less steep than active ones.
As continental crust erodes, it breaks
- Composition
- Continental rise, continental slope, continental shelf
- Oceanic area percentage
- 28%
- Shelf width range
- 0.03–1500 km
- Shelf mean slope angle
- 0° 07′
- Types
- Active and passive margins
- Sediment trapped
- 80% of stream load sediment
Lore & Background
The continental margin comprises three subzones. The continental shelf is the shallow, flat area near continents, ending at the shelf break where the slope angle increases drastically. The continental slope begins at the shelf break, descending 1–5 km to the deep-ocean floor, and often features V-shaped submarine canyons that cut into the shelf. At the base of the slope, the continental rise marks a decrease in slope angle and the transition to the abyssal plain.
Reader's Guide
There are two types of continental margins: active and passive. Active margins are associated with lithospheric plate boundaries, featuring high tectonic activity such as volcanoes and earthquakes, and are typically narrow with steep descents into trenches. Convergent active margins, where oceanic crust subducts beneath continental crust, are the most common; transform active margins are rarer. Passive margins lie within lithospheric plates away from boundaries, lack major tectonic activity, and are wider and less steep, often accumulating several kilometers of sediment. The continental shelf is the most economically valuable part of the ocean, hosting fishing grounds, oil and gas, sand, gravel, and heavy minerals. The United Nations Convention on the Law of the Sea (UNCLOS) uses the edge of the continental margin as a criterion for defining national claims to underwater resources, though the legal continental shelf may extend beyond the geomorphological one.
Did You Know?
- Continental margins constitute about 28% of the oceanic area.
- The width of continental shelves worldwide varies from 0.03 to 1500 km.
- Active margins are typically narrow from coast to shelf break, with steep descents into trenches.
- Passive margins often face mid-ocean ridges and lack major tectonic activity.
More in Structural Geology And Tectonics 1-24
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record