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Continental Shelf: Definition & Facts

Instructor: David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

After reading this lesson, you will be able to explain what a continental shelf is. You'll also be able to describe what happens beneath your feet as you walk out to sea and list some facts about continental shelves. A short quiz will follow.

What is a Continental Shelf?

It's a sunny day, with a beautiful, blue sky and so you head to the beach. You try to relax in the sun, but being such a good scientist, you can't help but notice things. You notice fish, crabs, and lots of other plant and animal life. But you also notice how flat the beach is and wonder, 'Is it this flat all the way out into the ocean?'

The Australian Continental Shelf (Light Blue)
The Australian Continental Shelf (Light Blue)

Time to investigate! You decide to go on a walk out into the ocean. At first, you're walking on the earth's continental crust. What is a crust? Well, the earth's crust is the rocky, top layer of the earth on which everything else sits: plants, humans, cities, and oceans. Continental crust is made of a mix of felsic and granitic types of rock.

You keep walking into the sea. The water gets gradually deeper as you go, but only at a super slow rate; it's still practically flat and shallow with no sharp drops. This is because you're actually walking on the continental shelf. It's called that because it's continental crust and it's shaped like . . . well, like a shelf.

Topography of a Continental Shelf
Topography of a Continental Shelf

What Happens When the Continental Shelf Ends?

As you continue to walk out into the ocean, the ground stays fairly flat for a long time. Pretty soon you need to snorkel across the surface because it gets too deep to stand.

You keep going until you notice something: suddenly the ground drops away below you. You have reached the shelf break, which is where the continental shelf ends. After this point, the ground descends steeply. This is called the continental slope.

Now, you need to scuba dive, because the ground has dropped so far down you can't see it. As you continue out into the ocean, you notice less plants and animals out here. Back on the continental shelf, you could barely step without crushing a living thing.

After a while, the steep slope lessens; this is called the continental rise. The ocean is still getting deeper, but at a much slower rate.

Cross Section of the Continental Shelf

Eventually, when the ocean is really, super deep, things change in a more fundamental way. Up until now, you were walking on and swimming above the continental crust. But now that you are snorkeling super deep, you left the continental crust behind you and reached the oceanic crust. Oceanic crust is a different kind of ground made of different types of rock; mafic and basaltic to be exact.

Oceanic crust and continental crust aren't connected together and can move in different directions to each other; when this happens, earthquakes shake and volcanoes erupt.

Continental Shelf Facts

Here are some facts about continental shelves:

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