Ocean Floor

Ocean Floor and Mapping

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As you go through the slides,

take notes on your Ocean Floor and Mapping packet.

Listen to the audio introduction. Click play.

SONAR - a technique of detecting objects underwater using sound waves.

• High-frequency sound waves are transmitted through water. The waves bounce off objects and are detected. The distance to an object is determined by measuring the amount of time required for the reflected sound wave to return to the device.

• The acronym “SONAR” stands for “SOund NAvigation and Ranging.”

Note-taking time

Be sure to copy the SONAR information from the last slide into your notes.
Only take notes on highlighted areas.

Using SONAR

Did you ever shout and hear an echo? If you did, that’s because the sound waves bounced off a hard surface and back to you. The same principle explains how sonar works. A ship on the surface sends sound waves down to the ocean floor. The sound waves bounce off the ocean floor and return to the surface, like an echo. 

Using SONAR

Sonar can be used to measure how deep the ocean is. A device records the time it takes sound waves to travel from the surface to the ocean floor and back again. Sound waves travel through water at a known speed. Once scientists know the travel time of the wave, they can calculate the distance to the ocean floor. They can then combine all of these distances to make a map of the ocean floor. 

Sea Floor Mapping Vocabulary (take notes)

• Coordinates – a set of numbers that describe where something is located. The location of a point on Earth’s surface is specified by its latitude and longitude.

• Latitude – a location’s distance north or south of the equator. Latitude is measured in degrees north or south.

• Longitude – a location’s distance east or west of the prime meridian. Longitude is measured in degrees east or west.

Multiple Choice

When using sonar, the distance to the ocean floor is calculated from the

• time it takes sound waves to travel to the ocean floor.

• pressure ocean water exerts on the ocean floor.

• speed of sound waves through ocean water.

• two of the answer choices are correct

Features on the Ocean Floor

Scientists have learned a lot about the ocean floor. For example, they know that Earth’s tallest mountains and deepest canyons are on the ocean floor. The major features on the ocean floor are described on the next slides. Be sure to take notes in your packet.

Ocean Floor Features

• The continental shelf is the ocean floor nearest the edges of continents. It has a gentle slope. The water over the continental shelf is shallow.

• The continental slope lies between the continental shelf and the abyssal plain. It has a steep slope with a sharp drop to the deep ocean floor.

• The continental rise is the area between the continental slope and abyssal plain.

Ocean Floor Features

• The abyssal plain forms much of the floor under the open ocean.

• An oceanic trench is a deep canyon on the ocean floor. Trenches occur where one tectonic plate subducts under another. The deepest trench is the Mariana Trench in the Pacific Ocean.

Ocean Floor Features

• A seamount is a volcanic mountain on the ocean floor. Seamounts that rise above the water surface are known as islands.

• The mid-ocean ridge is a mountain range that runs through all the world’s oceans.

Multiple Choice

The mid-ocean ridge forms where tectonic plates

• slide past one another.

• push together.

• pull apart.

• subduct.

Multiple Choice

Underwater mountain ranges, canyons, and trenches that extend around the world

• Mid Ocean Ridges

• Volcanoes

• Faults

Expanding Seafloor

• Ocean floor is made from cooling lava.

• Lava comes from the MANTLE at the ridge and cools.

• As more lava erupts, the crust moves away from the ridge.

• This is called SEAFLOOR SPREADING

What about the Old Ocean Floor?

• Old ocean floor moves edges of continents

• Trenches push ocean floor back to mantle

• RECYCLED!

• SUBDUCTION: crust pushing down into the mantle

Multiple Choice

The seafloor is recycled.

• True

• False

Multiple Choice

The crust going back down into the mantle is known as....

• Repurposing

• Transformation

• Subduction

Abyssal plains

•Abyssal plains are flat or very gently sloping areas of the deep ocean basin floor. They generally lie between the foot of a continental rise and a mid-oceanic ridge. 

Continental Rise

A gentle slope with a generally smooth surface, built up by the shedding of sediments from the continental block, and located between the continental slope and the abyssal plain. 

Mid-Ocean Ridge

A mid-ocean ridge is an underwater mountain range, typically having a valley known as a rift running along its spine, formed by a divergent plate boundary. It is usually an oceanic spreading center, which is responsible for seafloor spreading.

Multiple Choice

Which best represents the order of seafloor features as you move from the shoreline to the deep ocean?

•  Continental slope – continental shelf- continental rise – mid-ocean ridge
•  Continental rise – continental shelf – mid-ocean ridge -  continental slope
•  Continental shelf – continental slope – continental rise – mid-ocean ridge
•    Mid-ocean ridge – continental rise – continental shelf- continental slope

Multiple Choice

What is letter D?

• Cont. Shelf
• Mid-Ocean Ridge
• Volcanic Island
• Seamount

Multiple Choice

What is letter E?

• Volcanic Island
• Seamount
• Mid-Ocean Ridge
• Abyssal Plain

Multiple Choice

What is letter G?

• Mid-Ocean Ridge
• Rift
• Trench
• Cont. Shelf

Multiple Choice

The gradually sloping part of a continent that extends under the ocean is the...

• continental slope
• continental shelf
• abyssal plain
• trench

Multiple Choice

Seamount is similiar to...

• a volcanic island
• a small mountain or volcano
• The Great Plains
• The Grand Canyon

Multiple Choice

The continental slope is located at the end of the...

• shoreline
• continental shelf
• mid ocean ridge
• abyssal plain

Multiple Choice

The place where new ocean floor forms is called the...

• mid ocean ridge
• abyssal plain
• trench
• continental shelf

Multiple Choice

What is the difference between a volcanic island & a seamount?

• A volcanic island rises above the water & a seamount does not
• A seamount rises above the water & a volcanic island does not
• Both the seamount & volcanic island are underwater
• Both the seamount & the volcanic island rise above the water