Facts about Ocean Topography:
Beneath the world's oceans lie rugged mountains, active volcanoes, vast plateaus and
almost bottomless trenches. The deepest ocean trenches could easily swallow up the
tallest mountains on land.
Continental Shelf: Area of shallow water around most continents, reach depths of about
650 feet (200 m). The continental shelves end at the steeper continental slopes, which
lead down to the deepest parts of the ocean.
Abyss: Beyond the continental slope is the abyss. The abyss contains plains, long
mountains ranges called ocean ridges, isolated mountains called seamounts, and ocean
trenches which are the deepest parts of the oceans. In the centers of some ocean ridges
are long rift valleys, where Earthquakes and volcanic eruptions are common. Some
volcanoes that rise from the ridges appear above the surface as islands.
Other mountain ranges are made up of extinct volcanoes. Some seamounts, called
guyots, are extinct volcanoes with flat tops. Scientists think that these underwater
mountains were once islands but their tops were worn away by waves.
Area: nearly 71% of the Earth’s surface
Average Depth: 12,200 feet
Deepest Point: 36,198 feet in the Mariana Trench in the Western Pacific Ocean
Mountains: Ocean Ridges form the longest mountain range, almost 40,000 miles long,
largest single topographical feature on Earth
Highest Mountain: Mount Kea, Hawaii, rises 33,474 feet from its base on the ocean
floor, only 13,680 feet are above sea level (Mount Everest is 29,028 feet)
Measurement of Ocean Depth: Sonar instruments measure sound waves that are
bounced off the ocean floor and then recorded on board the ship. The speed of sound in
water is 1,500 m per second, four times faster than the speed of sound in air. By carefully
measuring the round-trip time of the sound waves and taking into account the variables of
temperature and salinity, the depth of the water and the distance to another object can be
measured accurately.
Seafloor Topography Images: Look at the colored satellite images of the ocean. The
red area around the continents is the continental shelf, the yellow is the continental slope.
The deep ocean is blue.
Bathymetry is the measurement of the depth of ocean water.
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