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Table of Contents - Special Paper 459

Hydrothermal Processes above the Yellowstone Magma Chamber: Large Hydrothermal Systems and Large Hydrothermal Explosions

by Lisa A. Morgan, W.C. Pat Shanks III, and Kenneth L. Pierce


Abstract 1
Introduction 3
Regional Geology 3
  Hydrothermal Explosions 3
  Large Hydrothermal Explosion Events in Yellowstone 7
  Importance of Hydrothermal Explosion Studies 7
Methodology and Fieldwork 10
  Field Methods 10
  Geochronology 13
  Chemistry, Mineralogy, Oxygen Isotope, and Fluid Inclusion Analyses of Hydrothermal Explosion Deposits 13
  Special Mapping Techniques 15
Results 15
  Large Hydrothermal Explosion Events in Yellowstone National Park 15
  Northern Basin of Yellowstone Lake and Vicinity 28
  Indian Pond Hydrothermal Explosion Crater 30
    Elliott’s Crater 30
    Turbid Lake 33
    Mary Bay Hydrothermal Explosion Crater 35
    Mary Bay hydrothermal explosion breccia 36
      Multiple events associated with the Mary Bay hydrothermal explosion 40
      Breccia-filled fractures along the original Mary Bay crater wall 42
      Preexisting hydrothermal system(s) prior to large explosion event at Mary Bay 42
      Sand beds underlying the Mary Bay explosion breccia 44
    Other Hydrothermal Explosion Craters North of Yellowstone Lake 45
      Sulfur Hills hydrothermal explosion crater 45
      Fern Lake hydrothermal explosion crater 46
      Hot Spring Geyser Basin 46
  West Thumb Geyser Basin 46
    Duck Lake Hydrothermal Explosion Crater 46
    Evil Twin Hydrothermal Explosion Crater 48
  Central Basin of Yellowstone Lake 52
    Frank Island Hydrothermal Explosion Crater 52
    Possible Explosion Craters East of Frank Island 52
  Lower Geyser Basin 52
    Twin Buttes 52
    Pocket Basin 52
  Norris-Mammoth Corridor 55
    Roaring Mountain 55
    Semi-Centennial Hydrothermal Explosion Crater 55
  Chemistry and Oxygen Isotopes of Hydrothermal Explosion Deposits 55
    Breccia Geochemistry 55
    Comparative Geochemistry 56
      Minor and trace elements 58
      Stable isotopes 61
  Related Hydrothermal Features 63
    Large Hydrothermal Domes 63
      Storm Point hydrothermal dome 63
      Domes on the floor of Yellowstone Lake 65
          North Basin hydrothermal dome (“inflated plain”)   65
    Joints 68
      Bridge Bay: Shallow deformation processes associated with hydrothermal fluids 68
      Storm Point joints 68
      Black Dog hydrothermal breccia pipe 69
    Collapse Craters and Dissolution 69
Discussion 69
  Controls on Distribution and Development of Hydrothermal Systems in Yellowstone National Park 71
    Influence of Lava Flows on Fluid Flow 71
    Local Structural Control 73
  Hydrothermal Processes Related to Alteration, Self-Sealing, and Dissolution 74
    Alteration, Dissolution, and Self-Sealing in Subaerial Environments 75
    Alteration, Dissolution, and Self-Sealing in Sublacustrine Environments 75
  Large Hydrothermal Explosions 76
    Triggering Mechanisms of Large Hydrothermal Explosions 78
      The Mary Bay hydrothermal explosion: An extreme event 80
    Energy Considerations for Large Hydrothermal Explosions in Yellowstone 81
  Recent Hydrothermal Explosions: Examples of Smaller Events in Yellowstone 81
  Potential Hazards Associated with Hydrothermal Explosions in Yellowstone 85
    Do Large Hydrothermal Domes Pose a Hazard in Yellowstone? 85
    Effects of Seasonal Lake Level Variations on Hydrothermal Venting in Yellowstone Lake 86
    Role of Seismicity 87
Conclusions 88
Acknowledgments 90
References Cited 91