Page 214 - NS-2 Textbook

OCEANOGRAPHY 209

Eruption of Myojin Reef Volcano, 170 miles south of Tokyo, Japan. The Java from this underwater volcano has pushed above the surface of
the Pacific to form a new island.

but those with flattened tops are called guyots. TIley Pacific floor is covered by this reddish clay. The land-
have been found in the Pacific but not in the Atlantic or derived muds consist of materials brought down by
Indian Oceans. The stacking of lava from repeated vol- rivers that flow into the oceans and spread over the
canic eruptions is believed to have created these guyots. abyssal plains by turbidity currents.
Their smooth, flat tops indicate that they were probably Sediment that builds up on the ocean floor does not
leveled off by wave action. It is believed that the always remain stationary. On the continental slopes!
great weight of the guyots caused them to sink into the great underwater landslides occur, especially in earth-
sea floor at the same time as the level of the ocean was quake zones. In some areas, slow bottmn currents move
rising. clay particles for hundreds of miles. Physical obstacles,
The Hawaiian Islands are a volcanic island chain. such as the continental shelf, ntid-ocean ridges, sublna-
Spectacular lava eruptions are regular occurrences frOln rine canyons and trenches, and seamounts cause chan-
a number of famous volcanoes in the islands. Kilauea neling and eddying of water flow. These actions result in
and Matma Loa on the big island of Hawaii are two of scouring in some areas on the edge of the abyssal plains
the world's most active volcanoes. Mauna Loa lifts its and deposits of great thickness in others.
head 13,677 feet above the blue waters of the Pacific. But The rate ofbuiJdup of the fine sediments on the deep
this is less than half of its real height, for from its base on seabed is very slo,v-about an inch every 2,500 years. Yet
the sea floor to its lava-covered summit, Matula Loa in some places the upper levels of the sea contain so
measures more than 31,000 feet. Other island chains of much microscopic plant and animal life that the seabed
this type include the Caroline, Gilbert, Samoan, and So- beneath is blanketed with thousands of feet of sediment
ciety Islands. (ooze) fronl their relnains. Underwater volcanic erup-
Sedi11leuts of the Deep Ocean Floor. The sediments of tions spread sediments for nmes. Volcanic ash and dust
the ocean floor consist of three general types of materials: from eruptions on the surface may circle the globe for
oozes, clays, and land-derived muds. The oozes are years before falling again to Earth's surface. Icebergs also
found in warm, shallower waters and are composed of deposit sediments in the ocean. River ice and ice formed
marine shells and skeletons of minute animals. Equato- along the shore will entrap detritlls (loose material) that
rial areas and the Atlantic Ocean have concentrations of gradually sinks to the bottom as the ice melts. Seismic
these oozes. A dark brown or reddish clay is fOtmd in the measurements indicate that there is 1,000-1,200 feet of
deep, cold parts of the ocean basin. It is made up of air- undisturbed sediments in areas of the deep oceans that
borne, volcanic, and meteorite dusts. Most of the North have a minimum of lUldenvater cunents.