The Geomorphic Footprints of Natural Hazards

Tim Davies is Professor in the School of Earth and Environment at University of Canterbury, New Zealand. Educated in Civil Engineering in UK in the 1970s, he taught in Agricultural Engineering and subsequently Natural Resources Engineering at Lincoln University, New Zealand before transferring to University of Canterbury in the present millennium to teach into Engineering Geology and Disaster Risk and Resilience. He has published a total of over 140 papers on a range of pure and applied geomorphology topics including river mechanics and management, debris-flow hazards and management, landslides, earthquakes and fault mechanics, rock mechanics and alluvial fans; natural hazard and disaster risk and resilience. Oliver Korup is Professor in the Institute of Environmental Sciences and Geography and the Institute of Geosciences, University of Potsdam, Germany. Following an academic training in Germany and New Zealand, his research and teaching is now at the interface between geomorphology, natural hazards, and data science. He has worked on catastrophic erosion and disturbances in mountain belts, particularly on landslides, natural dams, river-channel changes, and glacial lake outburst floods. John J. Clague is Emeritus Professor at Simon Fraser University. He was educated at Occidental College, the University of California Berkeley, and the University of British Columbia. He worked as a Research Scientist with the Geological Survey of Canada from 1975 until 1998, and in Department of Earth Sciences at Simon Fraser University from 1998 until 2016. Clague is a Quaternary geologist with research specializations in glacial geology, geomorphology, natural hazards, and climate change, and has authored over 200 papers on these topics. He is a Fellow of the Royal Society of Canada and an Officer of the Order of Canada.

Preface ix


Acknowledgements xiii


1 Natural Disasters and Sustainable Development in Dynamic Landscapes 1


1.1 Breaking News 1


1.2 Dealing with Future Disasters: Potentials and Problems 4


1.3 The Sustainable Society 5


1.4 Benefits from Natural Disasters 7


1.5 Summary 10


2 Defining Natural Hazards, Risks, and Disasters 13


2.1 Hazard Is Tied To Assets 13


2.1.1 Frequency and magnitude 14


2.1.2 Hazard cascades 16


2.2 Defining and Measuring Disaster 17


2.3 Trends in Natural Disasters 18


2.4 Hazard is Part of Risk 19


2.4.1 Vulnerability 19


2.4.2 Elements at risk 21


2.4.3 Risk aversion 23


2.4.4 Risk is a multidisciplinary expectation of loss 23


2.5 Risk Management and the Risk Cycle 24


2.6 Uncertainties and Reality Check 25


2.7 A Future of More Extreme Events? 26


2.8 Read More About Natural Hazards and Disasters 28


3 Natural Hazards and Disasters through The Geomorphic Lens 33


3.1 Drivers of Earth Surface Processes 34


3.1.1 Gravity, solids, and fluids 34


3.1.2 Motion mainly driven by gravity 36


3.1.3 Motion mainly driven by water 37


3.1.4 Motion mainly driven by ice 39


3.1.5 Motion driven mainly by air 40


3.2 Natural Hazards and Geomorphic Concepts 40


3.2.1 Landscapes are open, nonlinear systems 40


3.2.2 Landscapes adjust to maximise sediment transport 41


3.2.3 Tectonically active landscapes approach a dynamic equilibrium 43


3.2.4 Landforms develop toward asymptotes 44


3.2.5 Landforms record recent most effective events 46


3.2.6 Disturbances travel through landscapes 46


3.2.7 Scaling relationships inform natural hazards 48


4 Geomorphology Informs Natural Hazard Assessment 51


4.1 Geomorphology Can Reduce Impacts from Natural Disasters 51


4.2 Aims of Applied Geomorphology 53


4.3 The Geomorphic Footprints of Natural Disasters 54


4.4 Examples of Hazard Cascades 56


4.4.1 Megathrust earthquakes, Cascadia subduction zone 56


4.4.2 Postseismic river aggradation, southwest New Zealand 58


4.4.3 Explosive eruptions and their geomorphic aftermath, Southern Volcanic Zone, Chile 59


4.4.4 Hotter droughts promote less stable landscapes, western United States 59


5 Tools for Predicting Natural Hazards 63


5.1 The Art of Prediction 63


5.2 Types of Models for Prediction 66


5.3 Empirical Models 67


5.3.1 Linking landforms and processes 68


5.3.2 Regression models 70


5.3.3 Classification models 72


5.4 Probabilistic Models 73


5.4.1 Probability expresses uncertainty 74


5.4.2 Probability is more than frequency 77


5.4.3 Extreme-value statistics 80


5.4.4 Stochastic processes 81


5.4.5 Hazard cascades, event trees, and network models 83


5.5 Prediction and Model Selection 84


5.6 Deterministic Models 85


5.6.1 Static models 85


5.6.2 Dynamic models 86


6 Earthquake Hazards 95


6.1 Frequency and Magnitude of Earthquakes 95


6.2 Geomorphic Impacts of Earthquakes 97


6.2.1 The seismic hazard cascade 97


6.2.2 Post-seismic and inter-seismic impacts 99


6.3 Geomorphic Tools for Reconstructing Past Earthquakes 100


6.3.1 Offset landforms 101


6.3.2 Fault trenching 102


6.3.3 Coseismic deposits 104


6.3.4 Buildings and trees 107


7 Volcanic Hazards 111


7.1 Frequency and Magnitude of Volcanic Eruptions 111


7.2 Geomorphic Impacts of Volcanic Eruptions 113


7.2.1 The volcanic hazard cascade 113


7.2.2 Geomorphic impacts during eruption 114


7.2.3 Impacts on the atmosphere 115


7.2.4 Geomorphic impacts following an eruption 116


7.3 Geomorphic Tools for Reconstructing Past Volcanic Impacts 118


7.3.1 Effusive eruptions 118


7.3.2 Explosive eruptions 120


7.4 Climate-Driven Changes in Crustal Loads 124


8 Landslides and Slope Instability 131


8.1 Frequency and Magnitude of Landslides 131


8.2 Geomorphic Impacts of Landslides 134


8.2.1 Landslides in the hazard cascade 134


8.2.2 Landslides on glaciers 136


8.2.3 Submarine landslides 137


8.3 Geomorphic Tools for Reconstructing Landslides 137


8.3.1 Landslide inventories 137


8.3.2 Reconstructing slope failures 138


8.4 Other Forms of Slope Instability: Soil Erosion and Land Subsidence 141


8.5 Climate Change and Landslides 143


9 Tsunami Hazards 151


9.1 Frequency and Magnitude of Tsunamis 151


9.2 Geomorphic Impacts of Tsunamis 153


9.2.1 Tsunamis in the hazard cascade 153


9.2.2 The role of coastal geomorphology 154


9.3 Geomorphic Tools for Reconstructing Past Tsunamis 155


9.4 Future Tsunami Hazards 162


10 Storm Hazards 165


10.1 Frequency and Magnitude of Storms 165


10.1.1 Tropical storms 165


10.1.2 Extratropical storms 166


10.2 Geomorphic Impacts of Storms 167


10.2.1 The coastal storm-hazards cascade 167


10.2.2 The inland storm-hazard cascade 171


10.3 Geomorphic Tools for Reconstructing Past Storms 172


10.3.1 Coastal settings 173


10.3.2 Inland settings 174


10.4 Naturally Oscillating Climate and Increasing Storminess 175


11 Flood Hazards 181


11.1 Frequency and Magnitude of Floods 182


11.2 Geomorphic Impacts of Floods 183


11.2.1 Floods in the hazard cascade 183


11.2.2 Natural dam-break floods 185


11.2.3 Channel avulsion 189


11.3 Geomorphic Tools for Reconstructing Past Floods 190


11.4 Lessons from Prehistoric Megafloods 194


11.5 Measures of Catchment Denudation 196


11.6 The Future of Flood Hazards 198


12 Drought Hazards 205


12.1 Frequency and Magnitude of Droughts 205


12.1.1 Defining drought 206


12.1.2 Measuring drought 207


12.2 Geomorphic Impacts of Droughts 208


12.2.1 Droughts in the hazard cascade 208


12.2.2 Soil erosion, dust storms, and dune building 208


12.2.3 Surface runoff and rivers 210


12.3 Geomorphic Tools for Reconstructing Past Drought Impacts 211


12.4 Towards More Megadroughts? 215


13 Wildfires 219


13.1 Frequency and Magnitude of Wildfires 219


13.2 Geomorphic Impacts of Wildfires 221


13.2.1 Wildfires in the hazard cascade 221


13.2.2 Direct fire impacts 221


13.2.3 Indirect and post-fire impacts 222


13.3 Geomorphic Tools for Reconstructing Past Wildfires 225


13.4 Towards More Megafires? 227


14 Snow and Ice Hazards 231


14.1 Frequency and Magnitude of Snow and Ice Hazards 231


14.2 Geomorphic Impact of Snow and Ice Hazards 232


14.2.1 Snow and ice in the hazard cascade 232


14.2.2 Snow and ice avalanches 233


14.2.3 Jokulhlaups ¨ 236


14.2.4 Degrading permafrost 237


14.2.5 Other ice hazards 239


14.3 Geomorphic Tools for Reconstructing Past Snow and Ice Processes 240


14.4 Atmospheric Warming and Cryospheric Hazards 241


15 Sea-Level Change and Coastal Hazards 247


15.1 Frequency and Magnitude of Sea-Level Change 248


15.2 Geomorphic Impacts of Sea-Level Change 250


15.2.1 Sea levels in the hazard cascade 250


15.2.2 Sedimentary coasts 251


15.2.3 Rocky coasts 253


15.3 Geomorphic Tools for Reconstructing Past Sea Levels 254


15.4 A Future of Rising Sea Levels 257


16 How Natural are Natural Hazards? 263


16.1 Enter the Anthropocene 263


16.2 Agriculture, Geomorphology, and Natural Hazards 266


16.3 Engineered Rivers 270


16.4 Engineered Coasts 272


16.5 Anthropogenic Sediments 274


16.6 The Urban Turn 277


16.7 Infrastructure’s Impacts on Landscapes 278


16.8 Humans and Atmospheric Warming 279


16.9 How Natural Are Natural Hazards and Disasters? 281


17 Feedbacks with the Biosphere 287


17.1 The Carbon Footprint of Natural Disasters 287


17.1.1 Erosion and intermittent burial 289


17.1.2 Organic carbon in river catchments 291


17.1.3 Climatic disturbances 293


17.2 Protective Functions 296


17.2.1 Forest ecosystems 296


17.2.2 Coastal ecosystems 299


18 The Scope of Geomorphology in Dealing with Natural Risks and Disasters 309


18.1 Motivation 310


18.2 The Geomorphologist’s Role 312


18.3 The Disaster Risk Management Process 313


18.3.1 Identify stakeholders 313


18.3.2 Know and share responsibilities 314


18.3.3 Understand that risk changes 315


18.3.4 Analyse risk 316


18.3.5 Communicate and deal with risk aversion 317


18.3.6 Evaluate risks 319


18.3.7 Share decision making 321


18.4 The Future—Beyond Risk? 322


18.4.1 Limitations of the risk approach 323


18.4.2 Local and regional disaster impact reduction 323


18.4.3 Relocation of assets 325


18.4.4 A way forward? 325


19 Conclusions 329


19.1 Natural Disasters Have Immediate and Protracted Geomorphic Consequences 329


19.2 Natural Disasters Motivate Predictive Geomorphology 329


19.3 Natural Disasters Disturb Sediment Fluxes 330


19.4 Geomorphology of Anthropocenic Disasters 331


References 332


20 Glossary 333