     Because of its enormous size, the Pacific Ocean is often considered 
the principal physical feature of the earth.  It extends from Bering 
Strait to 60 south latitude--a northsouth distance of about 13,500 kilo-
meters (8,400 miles).  Its width along the equator is about 16,900 kilome-
ters (10,500 miles).  The total surface area of the Pacific is about 
180,000,000 square kilometers (70,000,000 square miles), or about one third 
of the earth's surface.  The Pacific is the world's deepest ocean.  About 
70 percent of its total bottom area is more than 3,900 meters (13,000 feet) 
below sea level.  This deep area-larger than the entire surface area of the 
Atlantic Ocean--is usually called the Pacific Basin.
     Boundaries.  The coastlines of North and South America form the 
eastern boundary of the Pacific.  The western boundary is more difficult to 
define because of the presence of many large islands separated from the 
Asian and Australian mainland's by shallow seas.
     Temperature of the Surface Waters.  The Pacific is a warm ocean.  Most 
of the surface water between the tropics of Cancer and Capricorn has a tem-
perature of well above 216XC (706XF).  Little cold water from the Arctic 
Ocean enters the Pacific through the Bering Strait.  But in the Southern 
Hemisphere, the Humboldt Current moves masses of cold water from the Ant-
arctic Ocean through the eastern Pacific toward the equator.  Most of the 
Pacific islands are on the western side of the ocean between the Tropic of 
Cancer and the Tropic of Capricorn.  They enjoy warm temperatures that 
change little from season to season.
     The Pacific Islands The Pacific islands fall into two very different 
groups_continental islands and oceanic islands.  The continental islands 
rise from the continental shelves and are composed of the same kinds of 
rocks that are found on the nearby continents-igneous, metamorphic, and 
sedimentary rocks.  Oceanic islands rise from the deep floor of the Pacific 
Basin.  They are composed of volcanic materials, coral, and limestone.  
There are thousands of volcanic islands and coral and limestone reefs 
spread throughout the Pacific Basin.
     The continental Islands of the Pacific.  These islands are really 
partially submerged mountain chains.  They belong to the long chain of 
mountains and volcanoes that border the Pacific Basin.  Because this 
mountain chain contains many volcanoes, it is often called the Circle of 
Fire or Ring of Fire.  The continental islands have a greater variety of 
rocks and more complex structures than do the oceanic islands.  Therefore 
they are more likely to contain mineral ores of value.
     Oceanic Islands of the Pacific.  Two different processes helped to 
form the Pacific oceanic islands.  These processes are volcanism and sub-
sidence.  Volcanism extrudes (pours out) lava from the interior of the 
earth.  Volcanism produces an island if enough lava is poured out to form 
a mass that reaches above sea level.  Hawaii is the largest and highest 
island formed by volcanism.  It has an area of 10,414 square kilometers 
(4,021 square miles).  Its summit, Mauna Kea, rises 4,208 meters (13,796 
feet) above sea level.
     The great weight of the lava forces the crust of the Pacific Basin to 
sink.  This process is called subsidence.  The older an island, the more 
it has sunk and the smaller it has become.  But while the volcanic island 
sinks, coral colonies living just below the surface sometimes build masses 
of coral on the sinking volcano.  In time the volcanic material may disa-
ppear beneath the ocean.  But the corals go on building upward, forming 
reefs just below the ocean surface.  If sand, formed by breakup of the 
coral rock, collects on top of the rock, a low sandy island results.  
If this sandy island is shaped like a ring, it is called an atoll.  In 
some cases masses of coral rock have been lifted above the surface by 
upward movement of the earth's crust.  Many islands of the Tonga group 
were formed in this way.
     It is easy to see a pattern in the distribution of these oceanic 
islands.  Volcanic activity has occurred along parallel cracks on the floor 
of the ocean.  In the Northern Hemisphere the most noticeable ridge forms 
the base of the Hawaiian Islands.  These islands spread along the ridge for 
about 2,400 kilometers (1,500 miles).  At the southeastern end of the is-
land chain is the highest island (Hawaii), which still contains several 
active volcanoes.  At the northwestern end of the chain are coral reefs 
and isolated rocks.
     2. PACIFIC OCEAN AND ISLANDS Oceania The islands of the Pacific are 
often called Oceania.  New Zealand, Australia, and the islands and island 
groups in the shallow waters off the Asian mainland (such as the Philippine 
Islands) are generally not considered part of Oceania.  The islands of Oce-
ania are divided into three main groups-Polynesia ("many islands"), Melan-
esia ("black islands"), and Micronesia ("small islands").
     Polynesia, the largest division, is made up of a large triangle of 
islands in the central and southeastern Pacific.  It includes French Pol-
ynesia; the Hawaiian Islands; Tonga; Tuvalu; American Samoa and Western 
Samoa; part of Kiribati; Easter, Midway, and Niue islands; and the Tokelau, 
Cook, Pitcairn, and Wallis and Futuna island groups.  New Zealand is some-
times included because the original Maori population is Polynesian.  Many 
Polynesian islands are the tops of volcanic mountains.  Others are atolls 
or coral islands.
     Melanesia, in the southwestern Pacific, includes Irian Jaya, in Indo-
nesia; New Caledonia; and the nations of Papua New Guinea, Vanuatu, the 
Solomon Islands, and Fiji.  The larger Melanesian islands are mountainous, 
and many of them are densely forested.
     The many small islands in northwestern Oceania are known as Micro-
nesia.  This region includes Naurn; Wake Island; part of Kiribati; and the 
Marshall, Caroline, and Marianas island groups.  Most of the islands of Mi-
cronesia are low-lying coral atolls.
     The People.  The peopleof Oceania are often divided into three ethnic 
groups that parallel the geographic division of the Polynesians form a 
distinct ethnic group.  Melanesians and Micronesians include peoples of 
many different origins.  The largestther groups on the islands are the 
Americans and the Japanese on the Hawaiian Islands and people of Indian 
descent, who outnumber the native Melanesians on Fiji.
     Polynesians share the same basic language and have common physical and 
cultural characteristics.  Before Europeans came to Oceania, Polynesians 
occupied almost all the islands of the South Pacific, as well as Hawaii and 
New Zealand.