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Driving Along the Ocean Floor by Patti Hutchison
If you could drive your car along the ocean floor, you would see some interesting formations. The ocean
floor has canyons, mountains, and plains just like the continents. But these formations are higher, wider, and
flatter than those on land. The ocean also has more volcanoes than the continents. Let's examine some of
these features.
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You may think that a continent ends at the shoreline. This is not true! A continent extends into the ocean.
The area where the continent meets the ocean floor is called the continental margin. This is a part of the
continent that is under water. There are three parts to a continental margin.
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This first part of the continental margin is called the continental shelf. This is a flat area that is covered with
shallow water. The average depth of the water here is about 130 meters. The continental shelf slopes gently
downward from the shoreline.
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The width of the continental shelf is different around the world. Off the coast of southeastern Florida, there
is almost no continental shelf. Off the shore of Siberia, it extends almost 1200 kilometers into the ocean.
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Some scientists believe that the continental shelves were exposed during the last Ice Age. During this time,
sea level was much lower than it is today. Great Britain was attached to Europe. Asia was linked with North
America by the Bering land bridge. And there was a large, solid mass of land which is now the islands of the
Bahamas. As the glaciers began to melt, sea level rose and covered these continental shelves.
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The continental shelf is rich with resources. The waters are full of fish and other sea life. There are also large
deposits of gas and oil.
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At the edge of the continental shelf is an area called the continental slope. This is where the crust of the
continent and the ocean crust meet. Most scientists consider this as the edge of a continent.
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Watch out here for turbidity currents! These are fast-moving currents that flow along the continental slope.
They can move as fast as thirty kilometers per hour. They can be formed by underwater earthquakes or large
storm waves.
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In some places, submarine canyons cut through the continental slope. These are very deep valleys that
have been cut into the rock. Some scientists think strong turbidity currents eroded some of these canyons.
Earthquakes may have formed others. Some of them are deeper than the Grand Canyon.
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The continental slope drops off steeply to the continental rise. The continental rise separates the
continental slope from the ocean floor. It is made of sediments. These are small rocks and the remains of
plants and animals.
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Many of these sediments have been washed down from the continental slope. They move in underwater
mudslides with the turbidity currents. They come to rest at the bottom of the continental slope.
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A continental rise can be several kilometers thick. It gradually gets thinner as it merges with the ocean
floor beyond the continental margin.
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The ocean floor has some interesting landforms. We have only begun to explore them!
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Fill out the brace map with the 3 parts of the continental margin. Then complete
the circle maps with information about each of the regions.
Driving Along the Ocean Floor: Part 2 by: Patti Hutchinson
As you drive past the continental rise on the ocean floor, you come to the ocean basins. These basins lie
above the thin oceanic crust. Ocean basins take up about sixty percent of the earth's surface. They contain
some very interesting land forms.
1
About five kilometers below sea level you will find wide abyssal plains. These are some of the flattest lands
on Earth. They are covered with sediments and rocks. Farther out on the abyssal plains, the bottom is covered
with ooze. This sediment is made from tiny organisms that are no longer living.
2
Deep sea trenches are the deepest parts of the ocean basins. They are long, narrow cracks that look like
canyons. The deepest spot known on earth is in the Pacific Ocean. It is called Challenger Deep in the Mariana
Trench. It is over 11,000 meters deep! The Pacific Ocean has more trenches than the Atlantic. The Pacific's
trenches are also deeper than those in the Atlantic.
3
Did you know that the largest mountain ranges on earth are not found on the land? They rise up from the
ocean floor. These mountains are called mid-ocean ridges. Their total length is over 65,000 kilometers. This is
more than the circumference of the earth. The average height of these mountains is 1500 meters.
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These mountain ranges run throughout all the oceans. They extend from the Arctic Ocean through the
middle of the Atlantic Ocean. This is called the Mid-Atlantic Ridge. The belt then runs around Africa to the
Indian Ocean. It then runs into the Pacific Ocean to the west coast of North America. This part is called the
East Pacific Rise.
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Mid-ocean ridges are formed by volcanic action. Molten material from the mantle flows up to the surface.
There, it cools and forms new crust. Many island chains such as the state of Hawaii are formed this way.
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Rift valleys run along mid-ocean ridges. These are crevices in the ocean floor. They can be up to fifty
kilometers wide and two kilometers deep. There are many volcanic eruptions and earthquakes here. Scientists
believe this is the center where new crust is formed. Rocks around these ridges teach scientists about changes
in the earth's crust.
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Driving Along the Ocean Floor: Part 3 by: Patti Hutchinson
As you drive along the mountains of the mid-ocean ridge, you see a spectacular sight- a volcano
erupting. We tend to think of volcanoes as high, rocky mountains on land. But most of the earth's volcanoes
are hidden below the sea. Scientists estimate that there are over 20,000 volcanoes rising from the ocean floor.
These volcanoes produce about 75% of the magma that rises to the earth's surface.
1
Underwater volcanoes form where the earth's plates meet. Sometimes these plates move over a hot spot.
The magma moves up through them. Other volcanoes are formed in a different way. One plate is pushed
below another. The bottom plate melts. The magma rises though the plate on top. Either way, the result is a
volcanic eruption.
2
Eruptions of volcanoes are not as violent under the ocean. When lava erupts into the cold water of the
ocean, a solid crust forms quickly. The increased pressure keeps the water from boiling even though
temperatures are much greater than one hundred degrees Celsius.
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Although most volcanoes are found deep below the ocean surface, some exist in more shallow water.
Eruptions of these volcanoes are much more violent. Water and lava explode into the air like a geyser.
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Hydrothermal vents, which are much like geysers, are often found near underwater volcanoes. These are
holes in the ocean floor. They can be small cracks or large formations that look like chimneys. They release hot
water, around 350 degrees Celsius, that is rich with minerals.Islands formed by volcanoes are some of the most
beautiful places on Earth. The ocean floor has been called the last frontier. If we really could drive along it, we
would discover more new fascinating facts about it.
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Many unusual life forms exist near hydrothermal vents. These include giant clams and large tubeworms.
Some strange-looking fish also live there. They eat the bacteria that live on the rich mineral compounds released by the vents. This is the only environment on Earth that does not depend on the sun for energy.
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Underwater volcanoes can be very destructive. If there is a violent eruption, it could cause a tsunami. This
is a huge wave, sometimes called a tidal wave. They can be over thirty feet tall by the time they reach the
shore. This would greatly harm coastal areas where people live.
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It's true that volcanoes can be harmful, but most underwater volcanic activity is actually helpful. One benefit is that volcanoes help release excess heat from the core and mantle. Without this release, the solid, upper
mantle could begin to melt. Volcanoes also form new land. Along mid-ocean ridges, Earth's crust is constantly
being renewed.
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Underwater volcanoes build up slowly. Most of them form cone-shaped mountains called seamounts.
Sometimes a seamount will erode and sink. It becomes a guyot. If a seamount continues to build high
enough, it will jut out of the water. An island is born. The Hawaiian Islands are an example of a chain of underwater volcanoes. Volcanic action keeps these islands building yet today.
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There are thousands of active volcanoes along the ocean floor. They are continually forming new land.
Use the information from parts 2 & 3 to complete the
multi-flow map about the causes and effects of
underwater volcanoes.