Ocean Floor and Mapping

Ocean Floor and Mapping

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.

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. It lies from 3 to 6 kilometers (1.9 to 3.7 miles) below the surface. Much of it is flat.

• 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. It plunges more than 11 kilometers (almost 7 miles) below sea level.

Ocean Floor Features

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

• The mid-ocean ridge is a mountain range that runs through all the world’s oceans. It is almost 64,000 kilometers (40,000 miles) long! It forms where tectonic plates pull apart. Magma erupts through the ocean floor to make new seafloor. The magma hardens to create the ridge.

Multiple Choice

The mid-ocean ridge forms where tectonic plates

• slide past one another.

• push together.

• pull apart.

• subduct.