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It's Only a Matter of Time...

Quick as a … canyon?

Slow changes

So, you've decided that a canyon would be an interesting landscape feature for your backyard. Choose a path, take the garden hose to simulate a river, turn it on and wait. How long? You'll wait a long, long time. Weathering and eroding a canyon, butte, valley or arch takes more than years, more than decades, or perhaps even centuries. You can visit a favorite geological location as an old person and it will look essentially the same as it does today. The rate of these changes is imperceptible; meaning you can't perceive or see it. In most cases, we simply don't live long enough.  

How old is that mountain?

Mountains can be growing as you will see later. Here we watch them shrink by weathering and erosion - slowly, imperceptibly, over time.

     
  • Young mountains are steep. Their tops can be above the timberline and have snow year round. The Himalayas are young mountains.
  • Middle-aged mountains take on a rounded shape. Trees may go right up to the top.
  • Old mountains are well-worn. They look more like hills. The Appalachians are old mountains.

 

 

How old is that stream?

Dead_Horse_pointStreams can also tell their age. A young, active stream runs in a straighter path. Older, lazier streams meander, or wind. They run more slowly. What about this picture of the Green River? Can you see the twists and turns? You don't see rushing water. The canyon walls are steep. This took some time. What's your verdict?

 

Quick changes

Other changes are sudden. Avalanches, landslides, and flash floods can erode, or move land very quickly.
 
  • Avalanche - a waterfall of snow and ice down a hill. They can travel over 100 mph, moving anything in their path: trees, rocks, soil, cabins, skiers, or cars.
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  • Landslide - is similar to an avalanche but instead of snow and ice it is composed of soil and rock. Landslides often happen after a fire. The fire destroys the plants. Plant roots help hold the soil and rock on the hill. Without the roots gravity and spring rains erode the hill down.
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  • Flash flood - if more rain falls than can be soaked into the soil, absorbed by plants, or channeled through waterways, it floods. Flash floods can erode more than 25 centimeters of soil in a few hours.
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    Updated October 24, 2008 by: Glen Westbroek

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