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Active & Passive Continental Margins

Andrew Hurry, Rebecca Gillaspy
  • Author
    Andrew Hurry

    Andrew has taught English language to students from kindergarten through university for over a decade. He holds bachelors' degrees in English literature and Philosophy from Hobart and William Smith Colleges and a master's degree in Multilingualism and Education from the University of the Basque Country.

  • Instructor
    Rebecca Gillaspy

    Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Comprehend active and passive continental margins through an overview, examples, and definitions. Learn about continental shelves, subduction zones, and tectonics. Updated: 01/07/2022

Continental Margins

Continental margins are the areas along the edges of tectonic plates where the rocks which make up the continents, meet the types of rocks which make up the ocean floor.

The planet Earth is made up of a number of layers, often compared to a multilayered cake. At the very center of the Earth is the core, first the inner core and then the outer core. The core is an extremely hot, extremely dense ball of mostly metals, such as iron and nickel. The next layer is the mantle, made up of solid rock and pockets of magma. The core and mantel are about equally as thick, though as the mantle encloses the core, the mantle makes up about 84% of the volume of the planet Earth, while the core makes up about 15%. The final 1% of the volume of the planet is the outer most layer, the crust.


The layers of the Earth

layers of the earth plate tectonics continental margins


The Earth's crust is also made up of layers, the top two being the lithosphere and the asthenosphere. The top layer of crust, the lithosphere, is made up of tectonic plates. These plates slowly move over the surface of the Earth (only a few centimeters a year), crashing into each other, sliding against one another, or being torn apart. These movements result in tectonic and seismic activity, which results in earthquakes, volcanoes, mountain building, and ocean creation.


The tectonic plates which make up the crust of the Earth

tectonic plates active passive continental margins


There are two basic types of tectonic plates :

  • Oceanic Plates - these young and dense areas of crust make up the ocean floor. They are mostly made of basalt, a type of rock created through the cooling of lava.
  • Continental Plates - these older and less dense areas of the crust make up the continents of the planet. These plates are mostly composed of rocks like granite which were cooled and solidified underground as magma.

The movements of these tectonic plates can be convergent, divergent, or parallel. The type of movement and the densities of the tectonic plates involved results in different types of tectonic and seismic activity at continental margins. This activity will then produce the various continental margin features associated with either active or passive margins. Rising mountain ranges, volcanoes, and deep ocean trenches are continental margin features associated with active margins, while flat coastal plains, rivers and estuaries, and wide continental shelves are continental margin features associated with passive margins.

Earth

When you are active, you are always on the go and have a lot of energy. When you're passive, you tend to lie around and things happen slowly. Planet Earth behaves in a similar way. It has active areas where earthquakes rattle the ground and volcanoes erupt, and it has passive areas where sediment slowly deposits and few earth-shaking occurrences happen. In this lesson, you will learn about these active and passive areas of the world, as you take a look at active and passive continental margins.

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  • 0:08 Earth
  • 0:39 Continental and Oceanic Crust
  • 1:43 Continental Margin
  • 2:27 Active Continental Margin
  • 4:05 Passive Continental Margin
  • 4:55 Lesson Summary
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Active Continental Margins

At areas where a continental plate converges with an oceanic plate, the tectonic and seismic activities, associated with an active margin, take place. As oceanic plates are denser than continental ones, the continents roll over the basalt, pushing the oceanic crust down into the asthenosphere, as if the continents were floating over the oceanic crust. This produces some common features at active continental margins:

  • Varied inland geography - as the continental plates push the oceanic plates down, the continental plate itself is pushed up. This results in the formation of mountain ranges. Mountains, sea cliffs, and short rivers are features of the inland half of an active continental margin.
  • Subduction zones - as the oceanic crust is pushed down, it enters the asthenosphere, and the basalt is melted, creating pockets of magma. The process of subduction is the reason oceanic plates are younger than continental ones, as the oceanic crust is "recycled".
  • Narrow continental shelf - the coastal areas around continents which are submerged under water, are continental shelves. At areas of active continental margins, the continental shelves are narrow, quickly dropping off into the subduction zone and the oceanic trench.
  • Ocean trenches - the process of subduction results in a steep slope from the continent to the ocean floor. At the base of this sloop, deep oceanic trenches are formed.
  • Volcanoes and earthquakes - the magma produced through subduction can be forced back to the surface through volcanic activity. Earthquakes can also result from the stress produced as the two tectonic plates push against each other.

Active Margin Example

Areas of active continental margins can be found around the world.

  • West coast of North and South America - the North American and South American tectonic plates are both being pushed westward, resulting in active continental margins on the pacific coasts as the Pacific plate is subducted. Various features typical of active continental margins can be found along these coasts. Mountains, such as the Andes in South America, are being pushed up, while volcanic activity is taking place throughout the region, famously in areas such as the Cascades Volcanic Province, which is home to Mt. St. Helens in the United States.


Mt St Helens in Washington State is a volcano resulting from the tectonic forces of an active continental margin

mt st helens volcano over active continental margin


  • East and South-East Asia - on the other side of the Pacific, the Euroasian continental plate is pushing against the Pacific oceanic plate. The Marianas Trench, the deepest ocean trench in the world, is a result of the subduction in this area. In addition to volcanic activity, numerous earthquakes strike this region as a result of these tectonic movements.
  • The Ring of Fire - both the west coasts of North and South America as well as East and South-East Asia are part of the Ring of Fire. This is a horse-shoe shaped area around the Pacific Ocean that is undergoing subduction, resulting in a high amount of volcanic activity. This Ring of Fire exists along active continental margins.


The Ring of Fire is the area along the active continental margins of the Pacific Plate

Ring of Fire along active continental margins


Passive Continental Margins

At areas of the lithosphere where continental and oceanic plates are not meeting, passive margins are found. These areas have low levels of tectonic and seismic activity, as no friction or stress is created by tectonic movements. These passive continental margins can share a number of characteristics.

Continental and Oceanic Crust

To understand active and passive continental margins, it's important to gain a basic understanding of the way our planet is put together. The earth is not a solid clump of rock. Instead, it has different layers comprised of different materials. You can relate the main layers of the earth to a hard-boiled egg. The yellow inner yolk of the egg relates to the earth's core, which is a very hot place.

The white part of the egg relates to the earth's mantle, which is the largest layer and also pretty hot. The mantle is mostly solid, but the rock and material within the mantle can melt and form magma, which is the hot, molten rock that we associate with volcanoes. The shell covering the egg relates to the earth's crust.

Like the eggshell, the earth's crust is relatively thin and can break into sections of crust or plates. The continental crust is the part of the earth's crust that makes up the continents. The oceanic crust is the part of the earth's crust that underlies the oceans.

Continental Margin

The continental crust is less dense than the material that makes up the underlying mantle, so it tends to float on top of the mantle and move around. Of course, even though we live on the continental crust, we do not feel this movement because it's very slow, in the range of about 1-10 centimeters during the course of a year.

The continental crust is also less dense than the oceanic crust, so the oceanic crust does not move as much. But, because the continental crust is moving, it can knock into the oceanic crust at a place called the continental margin. We can define the continental margin as the zone that separates the continental crust from the oceanic crust.

Active Continental Margin

So, as you can imagine, just about anywhere there is a large land mass meeting up with a large body of water, we would find a continental margin. But, not all continental margins are created equal. Some are active and some are passive. Active continental margins are continental margins that are tectonically active. When we look at the term 'tectonics' in geology, we see that it refers to the study of the deformation of the earth's rocky crust and the forces that cause this deformation.

So, an area of the world that is tectonically active would be an area where the rocky crust folds or deforms, as seen in mountain building. It would also be the site of earthquakes and volcanoes. The West Coast of the United States is a good example of an active continental margin. Earthquakes have been known to shake California and other west coast states, and the Aleutian Islands of Alaska have many highly active volcanoes.

Active continental margins tend to have a narrow continental shelf, which is the submerged border of the continent. So, the continent drops off quickly along an active margin and meets up with the more dense oceanic crust. Because the oceanic crust is heavier, it gets forced underneath the continental crust, carrying lots of rock toward the hotter mantle of the earth, where it can melt. This area where plates converge and one plate is driven below the other is called a subduction zone. This contributes to the earthquakes and volcanic activity that we see associated with active continental margins.

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Video Transcript

Earth

When you are active, you are always on the go and have a lot of energy. When you're passive, you tend to lie around and things happen slowly. Planet Earth behaves in a similar way. It has active areas where earthquakes rattle the ground and volcanoes erupt, and it has passive areas where sediment slowly deposits and few earth-shaking occurrences happen. In this lesson, you will learn about these active and passive areas of the world, as you take a look at active and passive continental margins.

Continental and Oceanic Crust

To understand active and passive continental margins, it's important to gain a basic understanding of the way our planet is put together. The earth is not a solid clump of rock. Instead, it has different layers comprised of different materials. You can relate the main layers of the earth to a hard-boiled egg. The yellow inner yolk of the egg relates to the earth's core, which is a very hot place.

The white part of the egg relates to the earth's mantle, which is the largest layer and also pretty hot. The mantle is mostly solid, but the rock and material within the mantle can melt and form magma, which is the hot, molten rock that we associate with volcanoes. The shell covering the egg relates to the earth's crust.

Like the eggshell, the earth's crust is relatively thin and can break into sections of crust or plates. The continental crust is the part of the earth's crust that makes up the continents. The oceanic crust is the part of the earth's crust that underlies the oceans.

Continental Margin

The continental crust is less dense than the material that makes up the underlying mantle, so it tends to float on top of the mantle and move around. Of course, even though we live on the continental crust, we do not feel this movement because it's very slow, in the range of about 1-10 centimeters during the course of a year.

The continental crust is also less dense than the oceanic crust, so the oceanic crust does not move as much. But, because the continental crust is moving, it can knock into the oceanic crust at a place called the continental margin. We can define the continental margin as the zone that separates the continental crust from the oceanic crust.

Active Continental Margin

So, as you can imagine, just about anywhere there is a large land mass meeting up with a large body of water, we would find a continental margin. But, not all continental margins are created equal. Some are active and some are passive. Active continental margins are continental margins that are tectonically active. When we look at the term 'tectonics' in geology, we see that it refers to the study of the deformation of the earth's rocky crust and the forces that cause this deformation.

So, an area of the world that is tectonically active would be an area where the rocky crust folds or deforms, as seen in mountain building. It would also be the site of earthquakes and volcanoes. The West Coast of the United States is a good example of an active continental margin. Earthquakes have been known to shake California and other west coast states, and the Aleutian Islands of Alaska have many highly active volcanoes.

Active continental margins tend to have a narrow continental shelf, which is the submerged border of the continent. So, the continent drops off quickly along an active margin and meets up with the more dense oceanic crust. Because the oceanic crust is heavier, it gets forced underneath the continental crust, carrying lots of rock toward the hotter mantle of the earth, where it can melt. This area where plates converge and one plate is driven below the other is called a subduction zone. This contributes to the earthquakes and volcanic activity that we see associated with active continental margins.

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Frequently Asked Questions

What are three major features of a passive continental margin?

Passive continental margins are low in tectonic and seismic activity. This means that the inland coast and the sea floor are gradually sloped through erosion. There are few earthquakes and long river systems which may create estuaries.

Is Antarctica a passive or active continental margin?

The continent of Antarctica is bounded by a passive continental margin. As a result, there is little tectonic or seismic activity.

What is the meaning of a continental margin?

A continental margin is the area where tectonic plates meet. This may result in the process of subduction, in which the denser oceanic plate is pushed down into the asthenosphere by the less dense continental plate.

Where are two locations of active continental margins?

Active continental margins can be found throughout the world. The western coasts of North and South America are one example of active continental margins, where mountains are being formed, volcanoes and earthquakes occur, and deep oceanic trenches are found. The east coast of Asia is another active continental margin where the deepest oceanic trench, the Marianas, can be found.

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