Sculpting the Earth

By Nimmer, Peter | The World and I, October 1998 | Go to article overview

Sculpting the Earth


Nimmer, Peter, The World and I


Featuring complex shapes, precipitous drops, And multiple geologic traits, canyons manifest Some of nature's most spectacular scenery.

Mother Nature's recipe for a good canyon: In a large basin, place a layer of soft rock a couple hundred feet thick, run a stream over it, and occasionally sprinkle on a pinch of rain. (For an extra special canyon, uplift a generous portion of the rock.) Bake the mixture for about a million years, but not too much longer.

Mother Nature has been making canyons for a long, long time. And she's gotten pretty good at it. The best way to enjoy one of these tasty treats is to go on a canyon hike. A walk through a steep-walled canyon can be one of the most stimulating outdoor experiences you will ever have. The combination of flowing water, water-polished rock, and sharp cliffs makes the occasion truly memorable. And each canyon is unique. One can be huge--Arizona's Grand Canyon covers an area larger than New York City-while another can be a slot no wider than your arm span.

As encapsulated by the above recipe, canyon building involves a few simple but essential components. A canyon starts to form when a river or stream passes over soft rock, frequently sandstone or limestone. The soft rock permits downward erosion by the running water. The area needs only sparse rainfall, to ensure that erosion occurs mainly at the bottom of the canyon, with little effect on the sharp edges of the canyon walls. If these conditions persist over time, the river can continue to cut into the underlying bedrock and steep-sided cliffs will be formed.

Canyons are therefore found in arid regions that typically receive most of the annual precipitation in one season. When rain comes to a desert, it is usually sudden, intense, and dramatic. Large amounts of rainfall-- sometimes the entire year's precipitation-can occur in just a few hours.

On the other hand, if the area is wet with regular rainfall, the river banks will be continually eroded and wide valleys instead of canyons will be formed. Moreover, in northern latitudes, ancient glaciers appear to have scoured out certain areas, generating wide rivers today. Canyons will occur only where limited rain causes little weathering over time.

Streams and rivers continue to cut down into bedrock until they reach what is called their base level, when they can no longer move sediment away. When a stream is young, it is elevated above base level, allowing its flow to be rapid enough to continue eroding the bed. But an old stream has a slower flow that is unable to carve out much more material, and the bed has been eroded down to base level.

When an area is uplifted by geologic forces, the base level may undergo sudden readjustment, so that old streams can begin to cut downward again. For instance, the Colorado Plateau experienced rapid uplift, so that old rivers such as the Colorado were suddenly able to erode more material. This process has generated dramatic features with complex scenery, including the unusual combination of steep canyon walls with wide meanders in the river's course.

The combination of water running over soft rock in an arid region can form a beautiful canyon in about a million years or so. But after several million years, canyons are eroded away and the river valley becomes wide.

How is it possible?

If you've been to a canyon, you may have wondered how a narrow stream could have the energy to carve out such huge amounts of rock. It seems just impossible! But tourists seldom glimpse the stream's true power, observable only when it's flooding.

If the area's topography is such that it funnels nearly all the rainwater into a single streambed, the volume of water is focused and magnified. In a narrow canyon, the result is a huge flash flood--a wall of water that unleashes tremendous power, changing the stream from a petty trickle to a raging torrent 10 feet deep, within minutes. …

The rest of this article is only available to active members of Questia

Sign up now for a free, 1-day trial and receive full access to:

  • Questia's entire collection
  • Automatic bibliography creation
  • More helpful research tools like notes, citations, and highlights
  • Ad-free environment

Already a member? Log in now.

Notes for this article

Add a new note
If you are trying to select text to create highlights or citations, remember that you must now click or tap on the first word, and then click or tap on the last word.
One moment ...
Default project is now your active project.
Project items

Items saved from this article

This article has been saved
Highlights (0)
Some of your highlights are legacy items.

Highlights saved before July 30, 2012 will not be displayed on their respective source pages.

You can easily re-create the highlights by opening the book page or article, selecting the text, and clicking “Highlight.”

Citations (0)
Some of your citations are legacy items.

Any citation created before July 30, 2012 will labeled as a “Cited page.” New citations will be saved as cited passages, pages or articles.

We also added the ability to view new citations from your projects or the book or article where you created them.

Notes (0)
Bookmarks (0)

You have no saved items from this article

Project items include:
  • Saved book/article
  • Highlights
  • Quotes/citations
  • Notes
  • Bookmarks
Notes
Cite this article

Cited article

Style
Citations are available only to our active members.
Sign up now to cite pages or passages in MLA, APA and Chicago citation styles.

(Einhorn, 1992, p. 25)

(Einhorn 25)

1

1. Lois J. Einhorn, Abraham Lincoln, the Orator: Penetrating the Lincoln Legend (Westport, CT: Greenwood Press, 1992), 25, http://www.questia.com/read/27419298.

Cited article

Sculpting the Earth
Settings

Settings

Typeface
Text size Smaller Larger Reset View mode
Search within

Search within this article

Look up

Look up a word

  • Dictionary
  • Thesaurus
Please submit a word or phrase above.
Print this page

Print this page

Why can't I print more than one page at a time?

Full screen

matching results for page

Cited passage

Style
Citations are available only to our active members.
Sign up now to cite pages or passages in MLA, APA and Chicago citation styles.

"Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences." (Einhorn, 1992, p. 25).

"Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences." (Einhorn 25)

"Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences."1

1. Lois J. Einhorn, Abraham Lincoln, the Orator: Penetrating the Lincoln Legend (Westport, CT: Greenwood Press, 1992), 25, http://www.questia.com/read/27419298.

Cited passage

Thanks for trying Questia!

Please continue trying out our research tools, but please note, full functionality is available only to our active members.

Your work will be lost once you leave this Web page.

For full access in an ad-free environment, sign up now for a FREE, 1-day trial.

Already a member? Log in now.