Geography Reference
In-Depth Information
Now take a look at the Appalachian Mountains, even though it may seem like a complete change
of subject. The Canyon “goes down” while the Appalachians “go up,” but not very grandly. Indeed,
while they sport a decent peak or two, nobody is going to call them “The Grand Mountains.” But they
used to be. As noted in Chapter 6, geologists estimate some of the Appalachians were once 30,000
feet high. That's higher than Mount Everest, the highest mountain on Earth. But those once-mighty
mountains got worn down and
carried away,
mainly by runoff from precipitation, making molehills
out of mountains.
And so the Grand Canyon and the Appalachians — two very different landforms — turn out
to have something fundamentally in common. A process of removal has shaped both of them.
That is, both have been shaped by gradational force.
Getting Carried Away
Just how does gradational force work, as for example when it turns a 30,000 foot high mountain of
yesteryear into a 3,000 foot high mountain of today? Basically, it's a two-part process. Gradational
force is part of nature, which has at its disposal mechanisms (described in the next section) that can
break great big rocks into tiny bits of rocks that are easily transportable. After that, another set of
mechanisms picks upthe tiny pieces andcarries them away.These twosets ofmechanisms are known
respectively as
weathering
and
mass wasting.
It may take them hundreds or thousands or even mil-
lions of years to turn a mountain into a molehill, but nature is in no rush. Indeed, it has all the time in
the world.
Weathering the Earth
Weathering refers to the natural processes that break rock into smaller and smaller pieces.
Weathering can be broken down into two types,
mechanical
and
chemical.
Mechanical weathering
