The Grand Canyon

1
The Grand Canyon
A water created landform
2
The WOW Factor
3
Why is the Canyon Grand?

• The River rises at 5,000m and so has great
  potential energy
• The Colorado Plateau has risen 3,000 m in the
  last 5 million years lifting the river above its
  base level
• The sedimentary rocks are easily eroded
• The discharge is variable and at times very high
• The local climate is very arid reducing
  vegetation and available moisture

4
The v shaped valley

• Vertical erosion depends on
• The height above base level
• The resistance of the rock
• The energy of the stream
• Slope erosion depends on
• The moisture available
• The resistance of the rock
• Permeability of the rock

5
Less resistant rocks like shale give gentle slopes
The oldest, most resistant rocks produce the
steepest valley sides
Taken from Landmark AS Geography Prosser, Raw and
Bishop, Published by Collins
6
Limestone permeable, resistant,
Shale impermeable, easily weathered,
Coconino sandstone very resistant,
Mixed sandstones and shales- some more resistant
than others
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The Side Valleys

• Faults such as Bright Angel are easily exploited
  by water
• The gradient of side valleys is very steep
• Occasional rainstorms cause sheet-wash and free
  sediment

8
Bright Angel Fault is a point of weakness
Shale
Redwall Limestone
9
Study the Cross-section through the canyon
a.     Describe the shape of the canyonb.    
Look at the exposures of limestone on the valley
sides. Do they produce steep cliffs or
gentle slopes?c.     What rock type consistently
produces relatively gentle slopes on the valley
sides?d.     Most of the beds of rock are
horizontal. Do you think this has affected the
profile in any way?e.     Why do you think the
valley at the base of the Canyon is narrower
than the canyon higher up?f.      How has the
climate of the area encouraged the formation of
the canyon?