Erosion and Landscape Evolution

Anatomy of a
Drainage
System

The
Continental
Divide,
Colorado

The Ideal Stream Cycle (W.M.
Davis, 1880)
Not a Literal Time Sequence
• Youth
• Maturity
• Old Age
• Rejuvenation

The Ideal Stream Cycle

Youthful Landscape, Utah

Young-Mature Landscape, California

Mature Landscape, Pennsylvania

Monadnock, Colorado

Monadnocks, Maine

Old Age Landscape, South America

Rejuvenation
• Some change causes stream to speed up and cut deeper.
– Uplift of Land
– Lowering of Sea Level
– Greater stream flow
• Stream valley takes on youthful characteristics but retains features of older stages as well.
• Can happen at any point in the cycle.

Rejuvenation

Rejuvenation, San Juan River,
Utah

Machu Picchu, Peru

Machu Picchu, Peru

The Onset of Old Age? Indiana

Why the Stream Cycle Doesn't
Explain Everything
• Changes in sea level during the ice ages
• Most landscapes have been repeatedly rejuvenated
• Seems to work best in stable interiors of
Africa, Australia and South America.

Superposed (Antecedent) Drainage
Streams Cut Right Through High Topography
• Crustal Uplift Across River
• Rejuvenation
• Buried Ridge

The
Ultimate
Antecedent
Drainage,
India-Nepal-
Tibet

Rejuvenated Peneplain

Devil’s Gap, Wyoming

The Huang
He: “China’s
Sorrow”
• 1887: 2,000,000 dead
• 1931: 3,700,000 dead
• 1938: The Chinese dynamite levees to slow the Japanese; half a million Chinese died.

River Diversions in the Caspian
Region

Why is the Danube Blue?

Arid and Humid Weathering
Compared
• Rain: Rare, May Be Seasonal, Often
Violent
• Soil: Thin or Absent
• Vegetation: Sparse-no Continuous Cover
• Chemical Weathering: Weak
• Episodic Processes Dominate

Arid Erosion Cycle
• Alluvial Fans
• Playa Lakes
• Pediments

Alluvial Fans, Utah

Old Arid Landscape

Deltas

Deltas, Greece

Yosemite Falls, California

Niagara Falls

Evolution of Niagara Falls

Lakes
Limited Lifetime
Thousands - Millions of
Yr.
How They Form:
• Grabens (Faulting)
– Tahoe 1600'
– Baikal 5600'
– Tanganyika 4000'
•
Scour
– Great Lakes to 1300'
– Great Slave L. 2000'
– Lake Winnipeg
Damming: Crustal movement, Landslide, etc.
Volcanic Collapse -
Crater Lake
Sinkholes
Kettle Ponds

How Lakes Die
• Eutrophication
• Infilling - Only Way to Destroy Very Deep
Lakes
• Drainage at Outlet
• Climate Change