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PASSIVE CONTINENTAL MARGIN ACTIVE CONTINENTAL MARGIN
Land Continental shelf Sea level
Land
Continental shelf
Sea level
Continental slope
Continental slope
Abyssal
5 km Ocean basin
5 km
plain
Continental rise
Oceanic
floor
trench
50 kilometers 50 kilometers
VE = 10X VE = 10X
Shelf
Shelf
Rift valley
Slope Slope
Sea level
Abyssal
Seamounts
5 km
Rise
plain
Trench
Mid-oceanic ridge
horizontal scale 50
______________ ___
Vertical exaggeration = = = 10X
50 kilometers vertical scale 5
(VE)
FIGURE 24.23 Profiles of seafloor topography. The vertical scales differ from the horizontal scales, causing vertical exaggeration, which
makes slopes appear steeper than they really are. The bars for the horizontal scale are 50 km long, while the same distance vertically
represents only 5 km, so the drawings have a vertical exaggeration of 10.
ocean, covered by about 4 to 6 km (about 2 to 4 mi) of seawater. Ocean or the Indian Ocean basin (Figure 24.24). A trench is a
The basin is mostly a practically level plain called the abyssal long, relatively narrow, steep-sided trough that occurs along the
plain and long, rugged mountain chains called ridges that edges of the ocean basins. Trenches range in depth from about 8
rise thousands of meters above the abyssal plain. The Atlantic to 11 km (about 5 to 7 mi) below sea level. The origin of ridges
Ocean and Indian Ocean basins have ridges that trend north and trenches was discussed in chapter 18.
and south near the center of the basin. The Pacific Ocean basin The ocean basin and ridges of the ocean cover more
has its ridge running north and south near the eastern edge. The than one-half of Earth’s surface, accounting for more of the
Pacific Ocean basin also has more trenches than the Atlantic total surface than all the land of the continents. The plain of

FIGURE 24.24 The location of some of the larger ridges and trenches of Earth’s ocean floor.

24-21 CHAPTER 24 Earth’s Waters 617