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Table of Contents - Special Paper 392

A Typology of Sculpted Forms in Open Bedrock Channels

by Keith Richardson and Paul Anthony Carling

Abstract 1
Introduction 1
  General Remarks on Bedforms in Open Bedrock Channels 3

Terminology and Definitions
5
  Introduction 5
  Erosion Mechanisms 5
  A Definition of Bedforms in Open Bedrock Channels 6
  Describing the Effect of Rock Structure on Channel Morphology 7
Structural versus Hydrodynamic Control of Morphology 7
    Structurally Influenced Channel Morphologies 9
  Further Definitions 10
    Simple, Compound, and Coalesced Forms 10
    Isolate and Conjugate Forms 11
    Sharp or Cuspate Edges 12
    Flutes and Scallops 12
    Furrows, Grooves, Runnels, Troughs, Welts, and Channels 13
    Potholes 14

A Typology of Bedrock Bedforms
14
  Introduction 14
  1. Concave Features 18
    1.1 Potholes 18
    1.2 Longitudinal Furrows 29
    1.3 Nonlongitudinal Furrows 43
    1.4 Furrow Complexes 46
    1.5 Overhanging Concave Features 48
    1.6 Shallow Concave Surfaces 50
  2. Convex and Undulating Surfaces 50
    2.1 Hummocky Forms 50
    2.2 Other Convex and Undulating Surfaces 53
  3. Composite Forms 55
    3.1 Obstacle Marks 56
    3.2 Hummocky Forms with Linear Depressions 60
    3.3 Convex Surfaces with Steep Lee Faces 63
  4. Solutional Forms 64
    4.1 Solution Pits and Pans 64
    4.2 Scallops 69
    4.3 Other Solutional Forms 74
  5. Tool Marks 75
    5.1 Percussion Marks 75
    5.2 Scratch Marks 77
  6. Large-Scale Sculpted Features 78
    6.1 Uniform Bed Gradient 78
    6.2 Variable Bed Gradient 79

Further Observations and Discussion
83
  Principles Applying to the Morphology of Bedrock Bedforms 83
    1. Continuity of Form 83
    2. Convergence of Form 84
    3. The Constructive Interference of the Flow Structures of Contiguous Bedforms 85
    4. The Prevalence of Sharp Transverse Crests 86
  The Origin of Two Types of Sharp-Crested Transverse Features 87
    Sharp-Crested Hummocky Forms and Scallops: A Comparison 87
    The Origin of Scallops 87
    The Evolution of Directional Scallop Planforms 90
    The Origin of Sharp-Crested Hummocky Forms 90
  The Development of Sharp Edges in General 92
    The Phenomenon of Sharp Edges in Bedrock Bedforms 92
    A Criterion for the Development of Sharp Edges 93
    Types of Sharp Edges 93
    Mean Flow Pathlines Associated with Active Sharp Edges 95
  Further Comments on the Interpretation of Bedforms in Open Bedrock Channels 97
    Bedforms as Indicators of Flow Patterns 97
    Bedforms as Indicators of the Relative Roles of Bedload and Suspended Load in Erosion 99
    The Relative Importance of Erosion by Suspended Load and Bedload: A Hypothesis 101
  The Influence of Substrate on Bedform Development in Open Bedrock Channels 102
    Bedforms in Carbonate Rocks 102
    Bedforms in Silicate Rocks 102
  The Scale of Bedforms in Open Bedrock Channels 103

Conclusions
104
Acknowledgments 105
References Cited 105