1.2 Ocean Basins
Structure of Ocean Basins
Ocean basins are large depressions in Earth's surface filled with seawater. They are bounded by continental margins and contain distinctive features formed by plate tectonics, sedimentation, and volcanic activity over millions of years.
Continental Margins
Passive Margins
- • Wide continental shelf (up to 500 km)
- • Gentle continental slope
- • Thick sediment accumulation
- • No tectonic activity
- • Example: East coast of North America
Active Margins
- • Narrow continental shelf
- • Steep continental slope
- • Deep ocean trenches
- • Earthquakes and volcanoes
- • Example: West coast of South America
Major Seafloor Features
Continental Shelf
Shallow submerged edge of continents, 0-200m depth, ~8% of ocean floor. Rich in marine life and resources.
Continental Slope
Steep transition from shelf to deep ocean, 200-4000m. Cut by submarine canyons.
Abyssal Plains
Flat deep-sea floor, 4000-6000m depth. Covered by fine sediments. ~40% of ocean floor.
Mid-Ocean Ridges
Underwater mountain chains where new crust forms. Total length over 65,000 km. Rises 2-3 km above abyssal plains.
Ocean Trenches
Deepest parts of ocean, formed at subduction zones. Mariana Trench: 10,994 m deep.
Submarine Features
Seamounts
Underwater volcanoes rising over 1000m. ~100,000 globally.
Guyots
Flat-topped seamounts, eroded at sea level then submerged.
Submarine Canyons
Deep V-shaped valleys cut into continental slope.