Fluvialism

Fluvialism

• Prior model stressed marine planation, based on need to explain “drift” and erratics
• Glacial ideas “freed” imagination to consider other ideas
• Relatively rapid shift to fluvial denudation in 1860s
• Early impact of American geology: western surveys documentation of landforms

Four key papers

• Jukes (1862)
  • Southern Ireland
    • Focus on geomorphology, regional drainage pattern, wind gaps
  • Basic idea
    • Originally flat surface with slight dip to south
    • Hard, folded “Old Red Sandstone” buried in softer rocks
      • East-west trending buried ridges
    • North-to-south flowing rivers erode valleys
    • ORS provides pinning points that slow valley erosion
    • Lateral streams erode softer rocks more quickly
    • Resulting in “stream capture” and total reorganization of drainage network.
• Ramsay (1863)
  • The Weald of southeastern England
    • Broad eroded anticline of Chalk, wind gaps
  • Basic idea
    • Originally flat surface with slight dip to south
    • Broad fold of Chalk buried among older rocks
    • North-to-south flowing rivers erode valleys
    • Chalk provides pinning points that slow valley erosion
    • Lateral streams erode more quickly
    • Result is the erosion of broad low area inside the fold with drainage to North Sea
    • Again, drainage totally reorganized
  • Originally interpreted as due to marine erosion
    • No marine deposits or beaches
    • Limited fetch in embayment would limit marine erosion
• Geikie (1865)
  • Landforms attributed to fluvial and other denudation processes
    • Chemical
      • Due to dissolution; may form caverns
    • Physical
      • Eolian: dunes and weathering
      • Frost/ice: ice wedging
      • Fluvial
        • Erosion of gullies and ravines
        • River channel formation
        • Alluvial fans
        • Deltas
        • Supplies sediment to beaches
  • Uses an imaginary traverse down a Scottish river
  • Very “modern” perspective on processes
• Geikie (1868-69)
  • Attempt to quantify rates of denudation
  • Calculations based upon estimates of sediment load of major rivers
  • Recognizes two types of erosion
    • Mechanical: transported sediment
    • Chemical: dissolved load, not included in calculation

  • River	Time to erode 1 foot	Time for flattening
    Po	729 yr	< 0.5 Myr
    Hoang Ho	1464 yr
    Rhone	1528 yr
    Ganges	2358 yr	2.5 Myr
    Nile	4723 yr
    Mississippi	6000 yr	4.5 Myr
    Danube	6846 yr

  • Strong uniformitarianism tone but acknowledges rates may not be constant
  • Rapid rates of denudation
    • Suggestion that geological time may be over-estimated

Davis (1899)

• Cycle of Landscape Evolution
• Ultimate success of fluvialism