The Changing Earth: Volcanoes, Weathering & Deposition

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  • 0:00 A Different World
  • 0:47 Volcanoes
  • 1:46 Weathering
  • 2:30 Deposition
  • 3:48 Lesson Summary
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Lesson Transcript
Instructor: Kevin Newton

Kevin has edited encyclopedias, taught middle and high school history, and has a master's degree in Islamic law.

While we may not see it every day, the world is always changing. In this lesson, with the help of an ill-informed tour guide, we will see how volcanoes, weathering, and deposition work to continually change the surface of our planet.

A Different World

Imagine you were on vacation in the Rocky Mountains of Colorado. You booked a tour and are regretting it, since it's clear that this guy has no idea what's going on. After all, you read the guidebook on the plane ride in and are pretty sure that there were no Coloradans at the signing of the Declaration of Independence. Still, he's going on and on, and you're supposed to be on vacation. But you've finally had it when he utters 'look at these majestic mountains that have always been here just like this!'

'Enough!', you scream.

Everyone looks at you as you take a deep breath. Calmly, you explain that the landforms are indeed changing. As some people give you a puzzled look, you explain that every day, all over the world, landforms are changing.


The tour guide is clearly not amused, but you don't care. You remember last year's vacation to Hawaii and what your very able tour guide from there told you. The Hawaiian Islands were formed from underwater volcanoes that erupted. Every time they erupted, the cooled lava formed rock, making the volcano taller. As a result, they eventually poked out of the water, but the process is still continuing. Because of this, the Hawaiian Islands are always growing, and in a few thousand years, there should be another island to the west. Granted, the Rocky Mountains were formed by the movement of tectonic plates, but just as Hawaii was changing, so, too, were the Rockies.

The tour guide gets a smug look on his face and says that all of that was a theory. You reply that it is a theory, but a pretty good one, and ask him if he has a better one. He dodges the question and says that since he can't see it happening, then it must not be able to be proved. The crowd looks back at you.


Luckily, you have visual evidence of changes that the Earth undergoes, too. You explain to the crowd that your best friend just sent you pictures from her trip to Cape Cod. She went to a cemetery where many of the tombstones had signs of weathering, by which physical, chemical, or biological methods tear apart a landform. In fact, she could barely read the names on some of the markers due to moss and other organisms growing on them. You explain that this is a very small-scale version of what happens elsewhere, as the Appalachians were once as high as the Rockies. However, the combination of mosses, acid rain, and hot summers and cold winters have reduced the once jagged mountains to a much smoother range.

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