Ocean Topography

Ocean Topography

Middle School

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Learning Objectives

• Define ocean topography and learn how sonar maps the ocean floor.

• Describe the main features of the ocean floor, like ridges and trenches.

• Explain how moving tectonic plates form major features on the ocean floor.

• Compare the different horizontal zones of the ocean: Intertidal, Neritic, and Oceanic.

Key Vocabulary

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Topography

The study of the elevation and natural features of the land, including the ocean floor.

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Sonar

A method using sound pulses to measure the time for an echo to return from the ocean floor.

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Continental Shelf

A shallow area of the seabed around a large landmass, which is part of the continent.

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Abyssal Plain

A very flat and smooth region of the deep ocean floor, covered in mud and sediment.

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Mid-Ocean Ridge

An underwater mountain chain where tectonic plates separate, creating a new ocean floor.

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Trench

A long, narrow, and very deep depression in the ocean floor, like the Marianas Trench.

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What is Ocean Topography?

• Ocean topography is the study of the shape and features of the ocean floor.

• Scientists use a technology called sonar to map the underwater landscape.

• Sonar sends a sound pulse from a ship down to the ocean floor.

• The echo sounding process measures the returning echo to calculate depth.

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Multiple Choice

How does sonar help oceanographers map the ocean floor?

• By taking photographs of the ocean surface.

• By drilling into the ocean floor to measure its thickness.

• By measuring the time it takes for a sound pulse to travel to the floor and echo back.

• By analyzing the temperature of the water at different depths.

Formation of Ocean Basins

• The ocean floor is shaped by the movement of tectonic plates.

• Ocean basins form at different types of plate boundaries.

• Divergent plate movement is the main cause of ocean basin formation.

Multiple Choice

Which type of tectonic plate movement is most responsible for forming a new ocean basin?

• Transform boundary

• Convergent boundary

• Convection currents

• Divergent boundary

Features of the Ocean Margin

• The continental landmass surrounds the ocean, and its edge is the coastline.

• The continental shelf is the shallow, submerged area of the continent.

• The continental slope and rise lead down to the deep ocean floor.

Multiple Choice

What feature is described as a relatively shallow part of the seabed that is geologically part of the continental crust?

• The Coastline

• The Continental Slope

• The Continental Shelf

• The Abyssal Plain

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Features of the Deep Ocean Floor

• The abyssal plain is a flat area in the deep ocean with sediment.

• ​Mid-ocean ridges are underwater mountain chains where a new ocean floor is made.

• Seamounts are underwater mountains; some may form volcanic islands like the Hawaiian Islands.

• Trenches are the deepest parts, like the very deep Marianas Trench.

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Multiple Choice

What is the name for a long, narrow, deep depression in the ocean floor?

• Abyssal Plain

• Trench

• Mid-Ocean Ridge

• Seamount

​Horizontal Ocean Zones

• The Intertidal Zone is between high and low tide markers.

• The Neritic Zone extends to the edge of the continental shelf.

• The Oceanic Zone is the vast open ocean beyond the shelf.

Multiple Choice

Which ocean zone is located between the low tide marker and the edge of the continental shelf?

• Neritic Zone

• Abyssal Zone

• Intertidal Zone

• Oceanic Zone

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Common Misconceptions about the Ocean Floor

Misconception	Correction
The ocean floor is completely flat.	It has mountains, trenches, and plains, just like continents.
All underwater mountains are volcanoes.	Many are, but some ranges are formed by separating tectonic plates.
The deepest part of the ocean is in the middle.	The deepest parts are trenches, which are located near continental edges.
Sonar is a type of camera.	Sonar uses sound waves and echoes to create maps.

Multiple Choice

How do divergent plate boundaries lead to the formation of mid-ocean ridges?

• They cause two plates to separate, allowing magma to rise and create a new ocean floor and underwater mountains.

• They cause two plates to collide, pushing the crust upward to form a ridge.

• They involve plates sliding past each other, which grinds up the rock into a long ridge.

• They create deep trenches that are then filled with sediment to form ridges.

Multiple Choice

What is the primary difference between the continental shelf and the abyssal plain based on their geologic characteristics?

• The continental shelf is a deep trench, while the abyssal plain is a shallow, flat area.

• The continental shelf is a volcanic mountain range, while the abyssal plain is made of continental crust.

• The continental shelf is part of the continental crust, while the abyssal plain is a flat area on the deep ocean floor.

• The continental shelf is covered in mud, while the abyssal plain is a shallow region near the coast.

Multiple Choice

A team of oceanographers discovers a new, very long underwater mountain range with a valley running down its center. What does this discovery suggest about the tectonic activity in that area?

• It suggests the area has no tectonic activity and the mountains are ancient volcanoes.

• It suggests a convergent plate boundary, where an ocean trench is being formed.

• It suggests a divergent plate boundary is present, where a new ocean floor is actively being created.

• It suggests a transform plate boundary, where two plates are sliding past one another.

Multiple Choice

New volcanic islands often form near mid-ocean ridges. How does this process support the theory of plate tectonics?

• It means that ocean trenches and ridges are both created by erosion from water.

• It proves that all islands are made when plates crash together and push land up.

• It suggests the ocean floor is not active and hasn't changed in millions of years.

• It shows that plates are moving apart, which lets magma come up from below and build an island.

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Summary

• Ocean topography describes the ocean floor's features, which are mapped using sonar.

• Tectonic plate movements shape the ocean floor, creating features like mid-ocean ridges.

• Major features include the continental shelf, abyssal plains, seamounts, and deep trenches.

• The ocean is divided into zones: the Intertidal, Neritic, and Oceanic zones.

Poll

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