Dunes

List of Figures xi Acknowledgements xv Introduction 1 Part One 1 Wind and Sand 7 Wind versus Bed 7 The Law of the Wall 8 Improving the wind/bed model 9 Lift-Off 12 Holding down by gravity 12 Holding down by cohesion 12 Raising by lift 13 Raising by drag 13 Raising by bombardment 14 Thresholds 14 Grain size 16 The slope of the bed 17 The dynamics of water content 17 Crusts 19 Pellets 20 Sand in Motion 20 Saltation 20 Streamers and other medium-scale patterns of saltating sand 22 Reptation 22 Creep 23 Other near-surface activity 23 Suspension 24 The vertical distribution of load and grain size 24 The saturation length 24 The fetch effect 26 The response of a loose bed to erosion by the wind 27 The Transport Rate 27 Shapes, densities and mixtures of size 29 Hard surfaces 30 Rough surfaces 30 Moisture, temperature and humidity 31 Rain 31 References 31 2 Ripples 32 Subtypes 35 Models 36 Flow response 36 Gravity wave 36 Saltation length 37 Shadow zone 37 Mathematical 37 Pattern 38 3 The Form and Behaviour of Free Dunes 39 Definitions 39 Early Stages 39 Start 39 Minimum size 40 The Profile of a Fully Grown Dune 41 Toe 41 Windward slope (or 'stoss slope') 43 Crest 45 Lee slope 46 Movement 53 Turnover time, bulk transport 56 Size 56 Flow-hierarchy models 57 Grain-size models 57 The time/supply model 58 References 58 Part Two 1000 to 10,000 m2; 100 to 1000 years 59 4 Pattern in Free Dunes 61 Definitions 61 Wind-Directional Regimes 62 Global winds 62 Local wind systems 62 The Classification of Wind-Directional Regimes 65 Wind-Directional Regimes and Dune Pattern 66 Transverse Dunes 66 Two-dimensional pattern: vertical and downwind 67 Two-dimensional pattern: horizontal and transverse to the wind 68 Self-organisation 69 Barchans 71 Quasi-transverse patterns 75 Linear Dunes 80 Introduction 80 Models of formation 82 Sand Sheets 88 Dunes with Distinctive Sand 90 Gravel dunes 90 Zibars 91 Clay dunes 92 Lunettes 92 Gypsum dunes 93 Diatomite sands 93 Volcanic sands 93 Snow and ice dunes 94 Niveo-aeolian deposits 94 References 94 5 Forced Dunes 96 Dunes Built around Bluff Obstacles 96 Climbing and echo dunes 96 Flanking and lee dunes 97 Cliff-top and falling dunes 99 Dunes on Gently Sloping Terrain 99 Reference 99 6 Dunes and Plants 100 Wind, Sand and Plants 100 Rigid objects 100 Spatial pattern 101 Porosity 102 Flexibility 102 Plants as living things 103 The broader time/space framework 104 Dunes among Plants 104 Nebkhas 104 Blowouts 107 Parabolic dunes 109 References 111 7 Coastal Dunes 112 Coastal Dunes and Climate 112 The Beach-Dune System 114 Exclusively Coastal Dunes 117 Embryo dunes 117 Fore-dunes ('frontal dunes' or 'retention ridges') 118 Tsunamis 120 Coastal sand sheets 120 References 121 Part Three >0.3 mm; 8 Sand Seas 125 Terms 125 Large Sand Seas 127 Growth and Development 127 Sand Seas in Tectonic Basins 129 Topographically Unconfined Sand Seas 131 Transfer between Sand Seas 133 9 A History of Dune Sand 134 Provenance 134 Recycling 137 Maturation 139 Mineralogy 139 Size characteristics 141 Shape and surface texture 141 Redness 144 Relationships between Dune Fields and the Sources of Their Sand 145 Source-bordering dune fields 145 Dune fields that have migrated away from their source 145 Sand seas that have taken sand from many local sources 146 The Australian sand seas and some aeolian sandstones 146 References 146 10 A History of Inland Dunes 147 Very Ancient Dunes: Siliceous Windblown Sandstones 147 The Emergence of Familiar Spatial and Dynamic Patterns 151 Dune Historiography 153 Dating 153 Dune-building environments 156 The long-term development of sand seas: sediment state 160 Quaternary Dune-Building Climates 160 Dunes in the Early- and Mid-Pleistocene 162 Late Pleistocene Dunes 163 The main theatres of dune formation in the Late Pleistocene 165 Dunes in the Holocene 175 The deglaciated North 176 The mid-latitudes 177 The semi-arid tropics 178 The present deserts 178 References 179 11 A History of Coastal Dunes 181 Long Sequences 181 Sea Level 181 Other Controls 182 Calcareous Aeolianite 184 Reference 185 12 Mars, Venus, Titan 186 Similarities 186 Differences 187 Sand 188 Ripples and Transverse Aeolian Ridges 190 Dunes 191 Mars 191 Venus 194 Titan 194 Reference 195 Part Four Care 197 13 Local, Short-Term Care ( Dunes in Deserts 199 Folk science 199 New approaches 200 Stabilised Dunes in Semi-Arid Areas 204 Coastal Dunes 204 References 207 14 Sustainability (>100,000 m2; >10 years) 208 Constraints 208 Complexity 208 Uncertainty 210 Environmental change 210 Sustainability 211 Coastal dunes 211 Stabilised inland dunes 212 References 213 Index 214