Physics of Glaciers (eBook)

Front Cover 1
Title Page 2
Copyright Page 3
Table of Contents 4
Preface to Fourth Edition 12
Preface to First Edition 13
Chapter 1. Introduction 14
1.1 Introduction 14
1.2 History and Perspective 15
1.3 Organization of the Book 19
Further Reading 22
Chapter 2. Transformation of Snow to Ice 24
2.1 Introduction 24
2.2 Snow, Firn, and Ice 24
2.2.1 Density of Ice 25
2.3 Zones in a Glacier 26
2.3.1 Distribution of Zones 28
2.4 Variation of Density with Depth in Firn 29
2.5 Snow to Ice Transformation in a Dry-snow Zone 32
2.5.1 Processes 32
2.5.2 Models of Density Profiles in Dry Firn 35
2.5.3 Reduction of Gas Mobility 38
2.6 Hoar Layers 39
2.7 Transformation When Meltwater Is Present 40
Further Reading 41
Chapter 3. Grain-Scale Structures and Deformation of Ice 42
3.1 Introduction 42
3.2 Properties of a Single Ice Crystal 43
3.2.1 Structure 43
3.2.2 Deformation of a Single Crystal 45
3.3 Polycrystalline Ice: Grain-scale Forms and Processes 46
3.3.1 Orientation Fabrics: Brief Description 46
3.3.2 Impurities and Bubbles 46
3.3.3 Texture and Recrystallization 48
3.3.4 Formation of C-axis Orientation Fabrics 56
3.3.5 Mechanisms of Polycrystalline Deformation 61
3.4 Bulk Creep Properties of Polycrystalline Ice 64
3.4.1 Strain Rate and Incompressibility 64
3.4.2 Deviatoric Stress 65
3.4.3 Bench-top Experiments: The Three Phases of Creep 65
3.4.4 Isotropic Creep Behavior 67
3.4.5 Controls on Creep Parameter A 77
3.4.6 Recommended Isotropic Creep Relation and Values for A 85
3.4.7 Anisotropic Creep of Ice 91
3.5 Elastic Deformation of Polycrystalline Ice 101
Appendix 3.1 101
Appendix 3.2: Data for Figure 3.16 102
Chapter 4. Mass Balance Processes: 1. Overview and Regimes 104
4.1 Introduction 104
4.1.1 Notes on Terminology 107
4.2 Surface Mass Balance 109
4.2.1 Surface Accumulation Processes 109
4.2.2 Surface Ablation Processes 112
4.2.3 Annual (Net) Balance and the Seasonal Cycle 113
4.2.4 Annual Glacier Balance and Average Specific Balances 115
4.2.5 Variation of Surface Balance with Altitude 115
4.2.6 Generalized Relation of Surface Balance to Temperature and Precipitation 117
4.2.7 Relation of Glacier-wide Balance to the Area-Altitude Distribution 121
4.3 Mass Balance Variations of Mountain Glaciers 122
4.3.1 Interannual Fluctuations of Balance 122
4.3.2 Cumulative Balance and Delayed Adjustments 124
4.3.3 Regional Variations of Mass Balance 126
4.4 Englacial Mass Balance 128
4.4.1 Internal Accumulation 128
4.4.2 Internal Ablation 128
4.5 Basal Mass Balance 129
4.5.1 Basal Accumulation 129
4.5.2 Basal Ablation 131
4.6 Mass Loss by Calving 134
4.6.1 The Calving Spectrum 135
4.6.2 Calving from Tidewater Glaciers 136
4.6.3 Calving from Ice Shelves 137
4.6.4 Calving Relations for Ice Sheet Models 140
4.7 Methods for Determining Glacier Mass Balance 140
4.8 Mass Balance Regimes of the Ice Sheets 144
4.8.1 Greenland Ice Sheet 144
4.8.2 Antarctic Ice Sheet 147
Further Reading 149
Chapter 5. Mass Balance Processes: 2. Surface Ablation and Energy Budget 150
5.1 Introduction 150
5.1.1 Radiation 151
5.1.2 Energy Budget of Earth’s Atmosphere and Surface 151
5.2 Statement of the Surface Energy Budget 153
5.2.1 Driving and Responding Factors in the Energy Budget 154
5.2.2 Melt and Warming Driven by Net Energy Flux 154
5.3 Components of the Net Energy Flux 155
5.3.1 Downward Shortwave Radiation 156
5.3.2 Reflected Shortwave Radiation 158
5.3.3 Longwave Radiation 161
5.3.4 Field Example, Net Radiation Budget 161
5.3.5 Subsurface Conduction and Radiation 163
5.3.6 Turbulent Fluxes 165
5.4 Relation of Ablation to Climate 173
5.4.1 Calculating Melt from Energy Budget Measurements 173
5.4.2 Simple Approaches to Modelling Melt 175
5.4.3 Increase of Ablation with Warming 178
5.4.4 Importance of the Frequency of Different Weather Conditions 181
5.4.5 Energy Budget Regimes 182
Further Reading 186
Chapter 6. Glacial Hydrology 188
6.1 Introduction 188
6.1.1 Permeability of Glacier Ice 189
6.1.2 Effective Pressure 190
6.2 Features of the Hydrologic System 190
6.2.1 Surface (Supraglacial) Hydrology 191
6.2.2 Englacial Hydrology 192
6.2.3 Subglacial Hydrology 194
6.2.4 Runoff from Glaciers 198
6.3 The Water System within Temperate Glaciers 207
6.3.1 Direction of Flow 207
6.3.2 Drainage in Conduits 210
6.3.3 Drainage in Linked Cavities 218
6.3.4 Subglacial Drainage on a Soft Bed 222
6.3.5 Summary of Water Systems at the Glacier Bed 225
6.3.6 System Behavior 227
6.4 Glacial Hydrological Phenomena 229
6.4.1 Jökulhlaups 229
6.4.2 Antarctic Subglacial Lakes 233
Further Reading 235
Chapter 7. Basal Slip 236
7.1 Introduction 236
7.1.1 Measurements of Basal Velocity 237
7.1.2 Local vs. Global Control of Basal Velocity 239
7.2 Hard Beds 242
7.2.1 Weertman’s Theory of Sliding 242
7.2.2 Observations at the Glacier Sole 246
7.2.3 Improvements to Weertman’s Analysis 247
7.2.4 Discussion of Assumptions 249
7.2.5 Comparison of Predictions with Observations 250
7.2.6 How Water Changes Sliding Velocity on Hard Beds 251
7.2.7 Sliding of Debris-laden Ice 263
7.2.8 Sliding at Sub-Freezing Temperatures 266
7.2.9 Hard-bed Sliding: Summary and Outlook 267
7.3 Deformable Beds 268
7.3.1 Key Observations 269
7.3.2 Till Properties and Processes 270
7.3.3 Constitutive Behaviors 277
7.3.4 Slip Rate ub on a Deformable Bed 282
7.3.5 Large-scale Behavior of Soft Beds 286
7.3.6 Continuity of Till 290
7.3.7 Additional Geological Information 292
7.4 Practical Relations for Basal Slip and Drag 293
Further Reading 296
Chapter 8. The Flow of Ice Masses 298
8.1 Introduction 298
8.1.1 Ice Flux 299
8.1.2 Balance Velocities 301
8.1.3 Actual Velocities 302
8.1.4 How Surface Velocities Are Measured 306
8.2 Driving and Resisting Stresses 308
8.2.1 Driving Stress and Basal Shear Stress 308
8.2.2 Additional Resisting Forces and the Force Balance 312
8.2.3 Factors Controlling Resistance and Flow 314
8.2.4 Effective Driving Force of a Vertical Cliff 320
8.3 Vertical Profiles of Flow 322
8.3.1 Parallel Flow 322
8.3.2 Observed Complications in Shear Profiles 324
8.4 Fundamental Properties of Extending and Compressing Flows 328
8.4.1 General Concepts 328
8.4.2 Uniform Extension or Compression 330
8.5 General Governing Relations 332
8.5.1 Local Stress-equilibrium Relations 333
8.5.2 General Solutions for Stress and Velocity 334
8.5.3 Vertically Integrated Force Balance 335
8.5.4 General Mass Conservation Relation (Equation of Continuity) 343
8.5.5 Vertically Integrated Continuity Equations 344
8.6 Effects of Valley Walls and Shear Margins 351
8.6.1 Transverse Velocity Profile Where Basal Resistance Is Small 352
8.6.2 Combined Effects of Side and Basal Resistances 353
8.7 Variations Along a Flow Line 359
8.7.1 Factors Controlling Longitudinal Strain Rate 359
8.7.2 Local-scale Variation: Longitudinal Stress-gradient Coupling 360
8.7.3 Large-Scale Variation 364
8.8 Flow at Tidewater Margins 366
8.8.1 Theory 366
8.8.2 Observations: Columbia Glacier 368
8.9 Ice Sheets: Flow Components 369
8.9.1 Flow at a Divide 370
8.9.2 Ice Streams 373
8.9.3 Ice Shelves 386
8.9.4 Transition Zone Between Grounded and Floating Ice 397
8.9.5 Flow Over Subglacial Lakes 398
8.10 Surface Profiles of Ice Sheets 398
8.10.1 Profile Equations 398
8.10.2 Other Factors Influencing Profiles 403
8.10.3 Relation Between Ice Area and Volume 408
8.10.4 Travel Times 409
8.10.5 Local-scale Relation of Surface and Bed Topography 410
Further Reading 411
Chapter 9. Temperatures in Ice Masses 412
9.1 Introduction 412
9.2 Thermal Parameters of Ice and Snow 413
9.3 Temperature of Surface Layers 414
9.4 Temperate Glaciers 418
9.4.1 Ice Temperature 418
9.4.2 Origin and Effect of Water 420
9.4.3 Distribution of Temperate Glaciers 421
9.5 Steady-state Temperature Distributions 422
9.5.1 Steady-state Vertical Temperature Profile 422
9.6 Measured Temperature Profiles 426
9.7 General Equation of Heat Transfer 429
9.7.1 Derivation of Equation 429
9.7.2 Boundary and Basal Conditions 432
9.8 Temperatures Along a Flow Line 433
9.8.1 Observations 434
9.9 Time-varying Temperatures 436
9.10 Temperatures in Ice Shelves 439
Chapter 10. Large-Scale Structures 442
10.1 Introduction 442
10.2 Sedimentary Layers 443
10.3 Foliation 443
10.3.1 Elongate Bubble Forms 447
10.3.2 Finite Strain 447
10.4 Folds 449
10.4.1 Folding in Central Regions of Ice Sheets 451
10.5 Boudinage 451
10.6 Faults 453
10.7 Implications for Ice Core Stratigraphy 454
10.8 Ogives and Longitudinal Corrugations 456
10.9 Crevasses 458
10.9.1 Patterns and Conditions for Occurrence 458
10.9.2 Crevasse Depth and Propagation 462
10.9.3 Related Tensional Features 464
10.10 Structural Assemblages 465
Further Reading 465
Chapter 11. Reaction of Glaciers to Environmental Changes 466
11.1 Introduction 466
11.2 Reaction to Changes of Mass Balance: Scales 467
11.2.1 Net Change of Glacier Length 468
11.2.2 Simple Models for Response 469
11.2.3 Simple Models for Different Zones 474
11.3 Reaction to Changes of Mass Balance: Dynamics 477
11.3.1 Theoretical Framework 477
11.3.2 Ice Thickness Changes 482
11.3.3 Relative Importance of Diffusion and Kinematic Waves 489
11.3.4 Numerical Models of Glacier Variation 490
11.4 Reactions to Additional Forcings 496
11.4.1 Response of Glaciers to Ice and Bed Changes 496
11.4.2 Factors Influencing the Reaction of an Ice Sheet to the End of an Ice Age 498
11.4.3 Ice Flow Increased by Water Input 503
11.5 Changes at a Marine Margin 507
11.5.1 Conceptual Framework 508
11.5.2 The Tidewater Glacier Cycle 513
11.5.3 Interactions of Ice Shelves and Inland Ice 516
11.5.4 Forcing by Sea-level Rise 521
Further Reading 523
Chapter 12. Glacier Surges 524
12.1 Introduction 524
12.2 Characteristics of Surging Glaciers 526
12.2.1 Spatial Distribution and Relation to Geological Setting 526
12.2.2 Distribution in Time 527
12.2.3 Temperature Characteristics 528
12.2.4 Characteristics of Form and Velocity 529
12.3 Detailed Observations of Surges 530
12.3.1 Surges of Temperate Glaciers 530
12.3.2 The Role of Water: Variegated Glacier 533
12.3.3 Surges Where the Bed Is Partly Frozen 536
12.3.4 Surges of Polythermal Tidewater Glaciers 539
12.4 Surge Mechanisms 541
12.4.1 General Evidence Relevant to the Mechanism 541
12.4.2 The Mechanism for Temperate Glaciers 545
12.4.3 Polythermal Glaciers 549
12.5 Surging of Ice Sheets? 550
12.6 Ice Avalanches 551
Chapter 13. Ice Sheets and the Earth System 554
13.1 Introduction 554
13.2 Interaction of Ice Sheets with the Earth System 555
13.2.1 Processes Driving Ice Sheet Change 556
13.2.2 Feedback Processes 561
13.3 Growth and Decay of Quaternary Ice Sheets 568
13.3.1 Relation to Milankovitch Forcings 570
13.3.2 Climate Forcings at the LGM 574
13.3.3 Onset of Quaternary Cycles 576
13.3.4 Heinrich Events 576
13.4 Ice Sheet Evolution Models 578
13.4.1 Model Components 578
13.4.2 Model Calibration 582
13.4.3 Simulations of Quaternary Ice Sheets 582
Further Reading 587
Chapter 14. Ice, Sea Level, and Contemporary Climate Change 588
14.1 Introduction 588
14.1.1 Equivalent Sea Level 589
14.1.2 Recent Climate and Sea-level Change 590
14.2 Global Warming and Mountain Glaciers 591
14.2.1 History of Glacier Lengths 592
14.2.2 Worldwide Mass Balance of Mountain Glaciers and Small Ice Caps 595
14.2.3 Sea-level Forecasts: Mountain Glaciers and Small Ice Caps 599
14.3 The Ice Sheets and Global Warming 603
14.3.1 Greenland 603
14.3.2 Antarctica 608
14.3.3 Model Forecasts of Ice Sheet Contributions to Sea-level Change 614
14.3.4 Simple Approaches to Forecasts for the Century Ahead 617
14.4 Summary 620
14.4.1 Recent Sea-level Rise 620
14.4.2 The Twentieth Century 621
14.4.3 This Century 621
Chapter 15. Ice Core Studies 624
15.1 Introduction 624
15.1.1 Some Essential Terms and Concepts 625
15.1.2 Delta Notation 625
15.2 Relation Between Depth and Age 627
15.2.1 Theoretical Relations 627
15.2.2 Determination of Ages 635
15.2.3 Difference of Gas and Ice Ages 643
15.3 Fractionation of Gases in Polar Firn 643
15.4 Total Air Content 647
15.5 Stable Isotopes of Ice 649
15.5.1 Conceptual Model 649
15.5.2 Interpretation of Records 657
15.6 Additional Techniques of Temperature Reconstruction 663
15.6.1 Borehole Temperatures 663
15.6.2 Melt Layers 664
15.6.3 Thermal and Gravitational Fractionation of Gases 665
15.7 Estimation of Past Accumulation Rates 665
15.8 Greenhouse Gas Records 667
15.8.1 Histories of Atmospheric Concentration 667
15.8.2 Isotopic Compositions of Greenhouse Gases 672
15.9 Gas Indicators of Global Parameters 672
15.9.1 Global Mean Ocean Temperature 672
15.9.2 Global Biological Productivity 673
15.10 Particulate and Soluble Impurities 673
15.10.1 Electrical Conductivity Measurement (ECM) 675
15.10.2 Primary Aerosols 675
15.10.3 Secondary Aerosols 677
15.11 Examples of Multiparameter Records from Ice Sheets 680
15.11.1 Deglacial Climate Change 680
15.11.2 A Long Record of Climate Cycling 680
15.12 Low-latitude Ice Cores 683
15.13 Surface Exposures in Ablation Zones 685
Further Reading 687
Appendix A: A Primer on Stress and Strain 688
Index 696
Color Plates 714