Lesson E6: Ocean Basins

Key Ideas     Unit Checklist

  Video Lesson

Why do rivers eventually flow to the ocean? Watch this video to learn more about drainage basins and ocean basins.

 
 

  Lesson E6: Ocean Basins


Figure E.2.6.1 – Ships use sonar to detect underwater objects.

Figure E.2.6.2 – Sonar machines send sound waves from a ship to the ocean floor.


Figure E.2.6.3 – Fish-finding machines contain sonar.
Reading and Materials for This Lesson

Science in Action 8
Reading: Pages 360–362

Materials:
No additional materials needed for this lesson.

Sound Waves for Mapping

Sonar is a technology that uses sound to detect objects in water. Sonar stands for “SOund Navigation And Ranging”.

A sonar machine on a ship sends sound waves into the water. These sound waves reflect off solid surfaces, and travel back to the ship, like an echo. The sonar machine measures how long it takes for the reflected sound waves to travel back to the boat. Using this time measurement and the speed of sound, the sonar machine can calculate how far away an underwater object is.

Sonar technology was used to map the ocean floor after the 1950s. Ships travelled back and forth on the ocean surface and measured the distance to the solid ocean floor. Sonar enabled scientists to detect features of the ocean floor, like underwater mountains, continental shelves, and deep trenches.

Sonar is still used by fishing boats today, to detect large schools of fish in the ocean. This technology has allowed fishers to catch large numbers of fish much easier than in the past.

 Watch More

Sonar

The deepest spot on Earth, the Mariana Trench, was discovered using sonar. Watch this video to learn more.

 
 
 
 
This video explains how scientists use sonar to study ocean ecosystems.

 
 

Lesson Activity


Figure E.2.6.4 – Ocean floor mapping. Image courtesy of the Australian Transport Safety Bureau.
Mapping Ocean Basins

 Problem:

Sonar technology on boats measures how long it takes for a reflected sound wave to travel from the ocean floor back to the boat. Scientists have measured the speed of sound through water as 1500 metres per second.

The relationship between speed, distance, and time is:

speed = distance âž— time

If we know the speed of a sound wave, and we know the amount of time that the sound wave travels back from the ocean floor to a boat, we can calculate the distance to the ocean floor by this relationship:

distance = speed âś– time
 
Download:

DOWNLOAD this document. It provides a sonar data table you will use to record your calculations of the distance of the ship to from the ocean floor. It also provides a grid for you draw dots to map ocean depth. It also has a place for you to answer questions at the end of the activity.

Instructions:

  1. The sonar data in this table was collected by a ship at 10 different locations on the ocean’s surface. The locations were equal distances apart. For each location, calculate the distance of the ship from the ocean floor. The speed of sound in water is 1500 metres per second.
 
Sonar Data
Location
1
2
3
4
5
6
7
8
9
10
Time for reflected sound waves to travel to ship
(seconds)		 0.5
0.5
1
2
3
3
1.5
3 
6
3
Distance of ship from ocean floor (ocean depth)
(metres)
                   
 

  1. Use the sonar data to draw a side-view profile of the ocean floor, on the graph below. At each location, draw a dot showing the ocean depth below the surface.



 

  1. Connect all the dots, from left to right.

  2. Examine your ocean basin profile. What ocean basin features do you observe at each location?

Analysis Questions:

Think about the following questions very carefully. Then, type or write your answers. When you have your answers, click the questions for feedback.

 
Sonar Data
Location
1
2
3
4
5
6
7
8
9
10
Time for reflected sound waves to travel to ship
(seconds)		 0.5
0.5
1
2
3
3
1.5
3 
6
3
Distance of ship from ocean floor (ocean depth)
(metres)
 750 750
1500
3000
4500
4500
2250
4500
9000
4500
 

 

 

There is a shallow, flat stretch of ocean floor between locations 1 and 2. This is a continental shelf.
The ocean floor is elevated at location 7. This is an underwater mountain.
The ocean floor plunges down at location 9. This is a deep sea trench.
Figure E.2.6.5 – Earth’s oceans contain several underwater mountain chains.
Figure E.2.6.6 – The Hawaiian volcano, Mauna Kea, is mostly under the ocean.


Figure E.2.6.7 – Magma flows out of cracks on the ocean floor to form mountains.
Underwater Mountains

Sonar mapping of the ocean floor led to the discovery of underwater mountains. Some underwater mountains form long ranges called mid-ocean ridges. Magma escapes Earth’s mantle at mid-ocean ridges, forming new rock on the ocean floor. During these underwater volcanic eruptions, ocean water becomes very hot. The hot water dissolves minerals from magma and rock. This adds salt to the ocean.

Sometimes underwater volcanoes build up enough rock to reach above the ocean’s surface. This is how the Hawaiian Islands were formed, including the mountain of Mauna Kea. Mauna Kea’s peak is 10 kilometres above its base on the ocean floor. That’s about one kilometer higher than Mount Everest, which is the world’s highest peak above sea level.

 Watch More

Underwater Volcanoes and Ridges

Watch this video to see a volcanic eruption on the ocean floor.

 
 
 
 
Watch this video to learn more about the Mid-Atlantic Ridge.

 
 

  Connections 

Figure E.2.6.8 – Offshore oil platforms pump oil from under the ocean floor.
Figure E.2.6.9 – Ships transport oil away from offshore oil rigs.


Figure E.2.6.10 – The Deepwater Horizon was an offshore drilling rig in the Gulf of Mexico.
Connections – Industry
>> Offshore Oil Drilling

Many oil deposits are located under the ocean floor. Oil from these deposits can be extracted by drilling offshore oil wells.

Offshore oil platforms support the machinery that is used to drill the well. Some oil platforms float, while others are fixed to the ocean floor. From the oil platform, a drill travels down through the water to the ocean floor. The drill travels even further as it then drills into rock. Oil from the drilled well is pumped up to the oil platform and loaded onto ships.  

Offshore drilling is much more complicated and risky than land-based oil wells. Waves and storms make it difficult to build and safely maintain oil platforms. Oil workers cannot easily go into the ocean to fix problems with offshore wells. Deep water work needs to be done by robots. If an offshore oil rig leaks oil, the health of ocean ecosystems is negatively impacted. The Deepwater Horizon was an offshore oil rig that exploded in 2010. The well spilled oil into the Gulf of Mexico for three months before engineers were able to cap the oil well.

 Watch More

The Challenges of Ocean Oil Drilling

Watch this video to learn more about offshore drilling.

 
 
 
 
Several offshore drilling operations are located off the coast of Newfoundland.

 
 
Figure E.2.6.11 – Continents around the world are divided into drainage basins.
Figure E.2.6.12 – Canadian rivers drain into five main bodies of seawater.












Figure E.2.6.13 – Water drains to different oceans on each side of a Continental Divide.
Water Draining from Land to Sea

Continents have multiple drainage basins, or watersheds. The high elevation borders between different drainage basins are called continental divides.

Alberta contains three different drainage basins. The water in northern Alberta rivers eventually flows to the Arctic Ocean. Most of southern Alberta’s rivers are in the Hudson Bay drainage basin. A small area in southeastern Alberta eventually drains into the Mississippi River and the Gulf of Mexico, which is connected to the Atlantic Ocean.

Because Alberta contains several drainage basins, it also contains several continental divides. The most well-known continental divide is the Great Continental Divide, which forms the jagged southern border between British Columbia and Alberta. West of the Great Continental Divide, water in British Columbia flows to the Pacific Ocean.

Not all rivers run to the ocean. Some rivers end up in endorheic drainage basins, which are low-lying inland areas. Endorheic basins often contain salty lakes. Some endorheic basins are very large, like Earth’s largest lake, the Caspian Sea. Others are small, like Alberta’s Pakowki Lake.

 Watch More

Drainage Basins

Watch this video to learn more about river drainage basins.

 
 
 
 
Watersheds are not just bodies of water – they involve land too. Watch this video to learn more.

 
 



  Make sure you have understood everything in this lesson. Use the Self-Check below, and the Self-Check & Lesson Review Tips to guide your learning.

Unit E Lesson 6 Self-Check

Instructions


Complete the following 6 steps. Don't skip steps – if you do them in order, you will confirm your understanding of this lesson and create a study bank for the future.

  1. DOWNLOAD the self-check quiz by clicking here.

  2. ANSWER all the questions on the downloaded quiz in the spaces provided. Think carefully before typing your answers. Review this lesson if you need to. Save your quiz when you are done.

  3. COMPARE your answers with the suggested "Self-Check Quiz Answers" below. WAIT! You didn't skip step 2, did you? It's very important to carefully write out your own answers before checking the suggested answers.

  4. REVISE your quiz answers if you need to. If you answered all the questions correctly, you can skip this step. Revise means to change, fix, and add extra notes if you need to. This quiz is NOT FOR MARKS, so it is perfectly OK to correct any mistakes you made. This will make your self-check quiz an excellent study tool you can use later.

  5. SAVE your quiz to a folder on your computer, or to your Private Files. That way you will know where it is for later studying.

  6. CHECK with your teacher if you need to. If after completing all these steps you are still not sure about the questions or your answers, you should ask for more feedback from your teacher. To do this, post in the Course Questions Forum, or send your teacher an email. In either case, attach your completed quiz and ask; "Can you look at this quiz and give me some feedback please?" They will be happy to help you!

Be a Self-Check

Superhero!



Self-Check Quiz Answers

Click each of the suggested answers below, and carefully compare your answers to the suggested answers.

If you have not done the quiz yet – STOP – and go back to step 1 above. Do not look at the answers without first trying the questions.

The drainage basin in northern Alberta leads to the Arctic Ocean, which is where this drop of water will end up.
Water flows downhill due to gravity. Road underpasses usually form small valleys under a road. This is a low-lying area where water can collect.
A continental divide exists between Lethbridge and Milk River. Water flows into different drainage basins on either side of the continental divide.
Offshore oil drilling often occurs in deep ocean water. It is expensive to build complex oil pumping machines that can reach great depths and withstand water movement. Building a large oil platform is also expensive, compared to a smaller conventional pump jack on land.
Due to gravity, water will always follow the shortest path downhill. The easiest downhill path for water is often into the valley of a larger stream. This is why water usually collects into progressively larger rivers, rather than every stream finding its own path to the ocean.