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the ocean basin alone, in fact, covers an area about equal to island. The Hawaiian Islands are examples of such giant vol-
the area of the land. Scattered over the basin are more than canoes that have formed islands. Most seamount-formed is-
10,000 steep volcanic peaks called seamounts. By definition, lands are in the Pacific Ocean. Most islands in the Atlantic, on
seamounts rise more than 1 km (about 0.6 mi) above the the other hand, are the tops of volcanoes of the Mid-Atlantic
ocean floor, sometimes higher than the sea-level surface of the Ridge. (For a worked example on this material, see the chapter 24
ocean. A seamount that sticks above the water level makes an resources at www.mhhe.com/tillery.)

SUMMARY

Precipitation that falls on the land evaporates, flows across the surface, An ocean wave is a moving disturbance that travels across the
or soaks into the ground. Water moving across the surface is called run- surface of the ocean. In its simplest form, a wave has a ridge called
off. Water that moves across the land as a small body of running water a crest and a depression called a trough. Waves have a characteristic
is called a stream. A stream drains an area of land known as the stream wave height, wavelength, and wave period. The characteristics of waves
drainage basin or watershed. The watershed of one stream is separated made by the wind depend on the wind speed, the time the wind blows,
from the watershed of another by a line called a divide. Water that collects and the fetch. Regular groups of low-profile, long-wavelength waves
as a small body of standing water is called a pond, and a larger body is are called swell. When swell approaches a shore, the wave slows and
called a lake. A reservoir is a natural pond, a natural lake, or a lake or pond increases in wave height. This slowing refracts, or bends, the waves so
created by building a dam for water management or control. The water of they approach the shore head-on. When the wave height becomes too
streams, ponds, lakes, and reservoirs is collectively called surface water. steep, the top part breaks forward, forming breakers in the surf zone.
Precipitation that soaks into the ground percolates downward until it Water accumulates at the shore from the breakers and returns to the sea
reaches a zone of saturation. Water from the saturated zone is called ground- as undertow, as longshore currents, or in rip currents.
water. The amount of water that a material will hold depends on its poros- Ocean currents are streams of water that move through other sea-
ity, and how well the water can move through the material depends on its water over large distances. Some ocean currents are density currents,
permeability. The surface of the zone of saturation is called the water table. which are caused by differences in water temperature, salinity, or sus-
The ocean is the single, continuous body of salt water on the pended sediments. Each ocean has a great system of moving water called
surface of Earth. A sea is a smaller part of the ocean with different a gyre that is centered in mid-latitudes. Different parts of a gyre are
characteristics. The dissolved materials in seawater are mostly the given different names such as the Gulf Stream or the California Current.
ions of six substances, but sodium ions and chlorine ions are the The ocean floor is made up of the continental shelf, the continental
most abundant. Salinity is a measure of the mass of salts dissolved in slope, and the ocean basin. The ocean basin has two main parts: the
1,000 g of seawater. abyssal plain and mountain chains called ridges.

KEY TERMS undertow (p. 613)
watershed (p. 600)
water table (p. 603)
abyssal plain (p. 617)
aquifer (p. 603)
breaker (p. 612) APPLYING THE CONCEPTS
continental shelf (p. 616)
continental slope (p. 616)
1. What is the most abundant compound near or on the surface of
divide (p. 602)
Earth?
freshwater (p. 598)
a. O 2
groundwater (p. 602) b. H 2 O
gyre (p. 615) c. CO 2
longshore current (p. 613) d. N 2
ocean (p. 607) 2. Evaporation, precipitation, and return of water to the oceans are
ocean basin (p. 616) called the
ocean currents (p. 614) a. rain cycle.
ocean wave (p. 610) b. aqueous cycle.
ridges (p. 617) c. hydrologic cycle.
d. geologic cycle.
rip current (p. 613)
salinity (p. 609) 3. What is the major source of freshwater?
a. Streams
sea (p. 607)
b. Underground water
submarine canyons (p. 616)
c. Precipitation
surf (p. 612)
d. Rivers
swell (p. 611)
trenches (p. 617)
618 CHAPTER 24 Earth’s Waters 24-22