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.
Your tour guide starts to open his mouth, but you’re not done. You explain to the crowd that just as weathering can break down a landform, other processes can add to it. Referring back to your friend in Cape Cod, you say that it’s not that the beach disappears, but it is re-deposited every year.
Such a process of adding sediments and rocks to a landform is known as deposition. Further, it doesn’t always have to be every year. To the north, the Canadian Shield was formed by a deposition of glaciers thousands of years ago in one giant deposit. As a result, the land is much more fertile than it would otherwise be.
Locking eyes with your tour guide, you ask if he’s sure that these mountains have never changed, or if he’d like to revise his previous statement. Flabbergasted, he throws his clipboard and runs off. Everyone around you looks confused, then a rather grandmotherly looking figure asks if you’d be willing to continue the tour. Others join the chorus, holding up their payments. You smile and oblige them, shouting just loud enough for the retreating and disgraced guide to hear, ‘and no Coloradan signed the Declaration of Independence!’
In this lesson, we looked at how landforms are changed by volcanoes, weathering, and deposition. Using the example of Hawaii, we saw how volcanoes add new land with every eruption.
Then, looking at Cape Cod, we learned that weathering, especially through water or air erosion or through other means, can turn a mountain into a hill, or change the coastline.Conversely, deposition does the exact opposite. It adds new material to a landmass, either adding land or causing existing features to level out. Beaches that do not disappear, yet change dramatically with major storms and tides, are examples of deposition. Likewise, the Canadian Shield was formed by the deposition of glaciers that have long since retreated.
The Changing Earth Overview
|Volcanoes||eruption rising and forcing land masses upward; the cooled lava forms rock|
|Weathering||physical, chemical, or biological methods tear apart a landform.|
|Deposition||adding sediments and rocks to a landform|
|Canadian Shield||formed by a deposition of glaciers thousands of years ago in one giant deposit|
When this lesson is over, you should be prepared to:
- Explain how the earth landforms may change over time
- Contrast volcanoes, weathering and deposition forms of change