Madeira Abyssal Plain

Deep-Ocean Basins

Deep-ocean trenches
Long, relatively narrow features
Deepest parts of ocean
Most are located in the Pacific Ocean  
Sites where moving lithospheric plates plunge into the mantle
Associated with volcanic activity
Volcanic island arcs
Continental volcanic arcs

Ocean Basin Floor

Abyssal plains
Likely the most level places on Earth
Sites of thick accumulations of sediment
Found in all oceans
Seamounts and guyots
Isolated volcanic peaks
Many form near oceanic ridges  

Seamounts and guyots
May emerge as an island
May sink and form flat-topped seamounts called guyots or tablemounts

The Oceanic Ridge

Mid-ocean ridge
Characterized by
An elevated position
Extensive faulting
Numerous volcanic structures that have developed on newly formed crust

Mid-ocean ridge
Interconnected ridge system is the longest topographic feature on Earth’s surface
Over 70,000 kilometers (43,000 miles) in length
Twenty-three percent of Earth’s surface
Winds through all major oceans
Along the axis of some segments are deep downfaulted structures called rift valleys

Mid-ocean ridge
Consist of layer upon layer of basaltic rocks that have been faulted and uplifted
Mid-Atlantic Ridge has been studied more thoroughly than any other ridge system