Transcript Erosion and Landscape Evolution

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-NepalTibet
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