Valleys are depressed areas of land–scoured and washed out by the conspiring forces of gravity, water, and ice. Some hang; others are hollow. They all take the form of a "U" or "V."
Rivers and streams make most primary valley cuts, carving steep-walled sides and a narrow floor that from afar looks like the letter "V." The gradient of the river—how quickly it drops—helps define the steepness of the sides and the width of the floor. Mountain valleys, for example, tend to have near-vertical walls and a narrow channel, but out on the plains, the slopes are shallow and the channel is wide.
As waters wind toward the sea, they add to natural twists in the land by stripping sediment from the outsides of bends and dumping it on the insides. The bulk of the rock and dirt is dredged from the bottom of the channel, a process called down cutting that can ultimately lead to deep, slender chasms like Black Canyon in Colorado's Gunnison National Park.
Types of Valleys
Some river and stream valleys, especially those in the mountains or located near the North and South Poles, are transformed by glaciers.
The massive blocks of snow and ice slowly creep downhill where they will meet the least resistance: valleys already cut by rivers and streams. As the glaciers ooze, they pick up rocks and grind away at the valley floor and sides, pressing the "V" into a "U." When the glacier melts, a U-shaped valley marks the spot where the snow and ice once flowed.
Side valleys are formed by tributaries to streams and rivers and feed the main stem. Where the main channel is carved deeper than the tributary, as commonly occurs during glaciations, the side valleys are left hanging. Waterfalls often cascade from the outlet of the upper valley into the drainage below.
Hollows, like those in Appalachia, are small valleys nestled between mountains or hills.
See Photos of Canyons
Giant valleys, called rifts, are found where two pieces of Earth's crust are separated or split apart. One such example is the Great Rift Valley, a rift system stretching from the Middle East to southern Africa.
You May Also Like
Go Further
Animals
- How can we protect grizzlies from their biggest threat—trains?How can we protect grizzlies from their biggest threat—trains?
- This ‘saber-toothed’ salmon wasn’t quite what we thoughtThis ‘saber-toothed’ salmon wasn’t quite what we thought
- Why this rhino-zebra friendship makes perfect senseWhy this rhino-zebra friendship makes perfect sense
- When did bioluminescence evolve? It’s older than we thought.When did bioluminescence evolve? It’s older than we thought.
- Soy, skim … spider. Are any of these technically milk?Soy, skim … spider. Are any of these technically milk?
Environment
- Are the Great Lakes the key to solving America’s emissions conundrum?Are the Great Lakes the key to solving America’s emissions conundrum?
- The world’s historic sites face climate change. Can Petra lead the way?The world’s historic sites face climate change. Can Petra lead the way?
- This pristine piece of the Amazon shows nature’s resilienceThis pristine piece of the Amazon shows nature’s resilience
- Listen to 30 years of climate change transformed into haunting musicListen to 30 years of climate change transformed into haunting music
History & Culture
- Meet the original members of the tortured poets departmentMeet the original members of the tortured poets department
- Séances at the White House? Why these first ladies turned to the occultSéances at the White House? Why these first ladies turned to the occult
- Gambling is everywhere now. When is that a problem?Gambling is everywhere now. When is that a problem?
- Beauty is pain—at least it was in 17th-century SpainBeauty is pain—at least it was in 17th-century Spain
Science
- Here's how astronomers found one of the rarest phenomenons in spaceHere's how astronomers found one of the rarest phenomenons in space
- Not an extrovert or introvert? There’s a word for that.Not an extrovert or introvert? There’s a word for that.
- NASA has a plan to clean up space junk—but is going green enough?NASA has a plan to clean up space junk—but is going green enough?
- Soy, skim … spider. Are any of these technically milk?Soy, skim … spider. Are any of these technically milk?
Travel
- This tomb diver was among the first to swim beneath a pyramidThis tomb diver was among the first to swim beneath a pyramid
- Dina Macki on Omani cuisine and Zanzibari flavoursDina Macki on Omani cuisine and Zanzibari flavours
- How to see Mexico's Baja California beyond the beachesHow to see Mexico's Baja California beyond the beaches
- Could Mexico's Chepe Express be the ultimate slow rail adventure?Could Mexico's Chepe Express be the ultimate slow rail adventure?