Erosion of steepland valleys by debris flows

Episodic debris flows scour the rock beds of many steepland valleys. Along recent debris-flow runout paths in the western United States, we have observed evidence for bedrock lowering, primarily by the impact of large particles entrained in debris flows. This evidence may persist to the point at which debris-flow deposition occurs, commonly at slopes of less than ∼0.03–0.10. We find that debris-flow–scoured valleys have a topographic signature that is fundamentally different from that predicted by bedrock river-incision models. Much of this difference results from the fact that local valley slope shows a tendency to decrease abruptly downstream of tributaries that contribute throughgoing debris flows. The degree of weathering of valley floor bedrock may also decrease abruptly downstream of such junctions. On the basis of these observations, we hypothesize that valley slope is adjusted to the long-term frequency of debris flows, and that valleys scoured by debris flows should not be modeled using conventional bedrock river-incision laws. We use field observations to justify one possible debris-flow incision model, whose lowering rate is proportional to the integral of solid inertial normal stresses from particle impacts along the flow and the number of upvalley debris-flow sources. The model predicts that increases in incision rate caused by increases in flow event frequency and length (as flows gain material) downvalley are balanced by rate reductions from reduced inertial normal stress at lower slopes, and stronger, less weathered bedrock. These adjustments lead to a spatially uniform lowering rate. Although the proposed expression leads to equilibrium long-profiles with the correct topographic signature, the crudeness with which the debris-flow dynamics are parameterized reveals that we are far from a validated debris-flow incision law. However, the vast extent of steepland valley networks above slopes of ∼0.03–0.10 illustrates the need to understand debris-flow incision if we hope to understand the evolution of steep topography around the world.

[1]  D. Montgomery,et al.  Field measurements of incision rates following bedrock exposure: Implications for process controls on the long profiles of valleys cut by rivers and debris flows , 2005 .

[2]  J. Major,et al.  Debris-flow deposition: Effects of pore-fluid pressure and friction concentrated at flow margins , 1999 .

[3]  J. Franklin,et al.  LOGGING THE MECHANICAL CHARACTER OF ROCK , 1971 .

[4]  R. Bagnold.  Experiments on a gravity-free dispersion of large solid spheres in a Newtonian fluid under shear , 1954, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[5]  D. F. McTigue,et al.  A Nonlinear Constitutive Model for Granular Materials: Application to Gravity Flow , 1982 .

[6]  I. Finnie,et al.  The Mechanism of Material Removal in the Erosive Cutting of Brittle Materials , 1966 .

[7]  S. F. Personius,et al.  Late Quaternary stream incision and uplift in the forearc of the Cascadia subduction zone , 1995 .

[8]  K. Thuro.  Drillability prediction: geological influences in hard rock drill and blast tunnelling , 1997 .

[9]  W. Weber,et al.  Solid-particle erosion of Portland cement and concrete , 1999 .

[10]  A. Howard.  A detachment-limited model of drainage basin evolution , 1994 .

[11]  I. Finnie.  Erosion of surfaces by solid particles , 1960 .

[12]  L. Benda,et al.  Stochastic forcing of sediment supply to channel networks from landsliding and debris flow , 1997 .

[13]  D. Inman,et al.  Observations of rapidly flowing granular-fluid materials , 1985, Journal of Fluid Mechanics.

[14]  Charles S. Campbell,et al.  RAPID GRANULAR FLOWS , 1990 .

[15]  R. Scattergood,et al.  Erosion of Silicon Single Crystals , 1980 .

[16]  Torsten Schaub,et al.  The variability of root cohesion as an influence on shallow landslide susceptibility in the Oregon Coast Range , 2001 .

[17]  P. Haff.  Grain flow as a fluid-mechanical phenomenon , 1983, Journal of Fluid Mechanics.

[18]  P. G. Fookes,et al.  A revision of the graphical method for assessing the excavatability of rock , 1994, Quarterly Journal of Engineering Geology.

[19]  Effect of Shear Surface Boundaries on Stress for Shearing Flow of Dry Metal Powders—An Experimental Study , 1987 .

[20]  S. Savage,et al.  Stresses developed by dry cohesionless granular materials sheared in an annular shear cell , 1984, Journal of Fluid Mechanics.

[21]  P. Earle,et al.  Survey of precursors to P'P': Fine structure of mantle discontinuities , 2003 .

[22]  L. Benda,et al.  Predicting deposition of debris flows in mountain channels , 1990 .

[23]  S. Savage,et al.  The motion of a finite mass of granular material down a rough incline , 1989, Journal of Fluid Mechanics.

[24]  J. F. Woodruff.  Debris Avalanches as an Erosional Agent in the Appalachian Mountains , 1971 .

[25]  J. H. Neilson,et al.  Erosion by a stream of solid particles , 1968 .

[26]  David R. Montgomery,et al.  Geologic constraints on bedrock river incision using the stream power law , 1999 .

[27]  G. Tucker,et al.  Dynamics of the stream‐power river incision model: Implications for height limits of mountain ranges, landscape response timescales, and research needs , 1999 .

[28]  M. Lockwood.  The case for transient magnetopause reconnection , 1996 .

[29]  M. E. Gulden,et al.  Impact damage in brittle materials in the elastic-plastic response régime , 1978, Proceedings of the Royal Society of London. A. Mathematical and Physical Sciences.

[30]  M. Brandon,et al.  Late Cenozoic exhumation of the Cascadia accretionary wedge in the Olympic Mountains, northwest Washington State , 1998 .

[31]  R. Goodman.  Introduction to Rock Mechanics , 1980 .

[32]  R. Kochel,et al.  Role of debris flows in long-term landscape denudation in the central Appalachians of Virginia , 2003 .

[33]  奥西 一夫,et al.  MOTION, DEBRIS SIZE AND SCALE OF DEBRIS FLOWS IN A VALLEY ON MOUNT YAKEDAKE, JAPAN , 1990 .

[34]  J. Jenkins,et al.  A theory for the rapid flow of identical, smooth, nearly elastic, spherical particles , 1983, Journal of Fluid Mechanics.

[35]  Masayuki Watanabe,et al.  Investigation and analysis of volcanic mud flows on Mt Sakurajima, Japan , 1981 .

[36]  D. J. Bogucki.  Debris Slides in the Mt. Le Conte Area, Great Smoky Mountains National Park, U.S.A. , 1976 .

[37]  Brian R. Lawn,et al.  Strength Degradation of Glass Impacted with Sharp Particles: I, Annealed Surfaces , 1979 .

[38]  J. C. Jaeger,et al.  Fundamentals of rock mechanics , 1969 .

[39]  K. Gahr,et al.  Microstructure and Wear of Materials , 1987 .

[40]  Richard M. Iverson,et al.  Flow of variably fluidized granular masses across three‐dimensional terrain: 1. Coulomb mixture theory , 2001 .

[41]  G. Tucker,et al.  Implications of the shear stress river incision model for the timescale of postorogenic decay of topography , 2003 .

[42]  David R. Montgomery,et al.  Shallow landsliding, root reinforcement, and the spatial distribution of trees in the Oregon Coast Range , 2003 .

[43]  P. Rosen,et al.  Updated repeat orbit interferometry package released , 2004 .

[44]  F. Nakamura,et al.  Dendrochronological analysis of debris flow disturbance on Rishiri Island , 1997 .

[45]  Dorothy J. Merritts,et al.  Geomorphic response of coastal streams to low, intermediate, and high rates of uplift, Medocino triple junction region, northern California , 1989 .

[46]  R. Drew,et al.  Wettability and spreading kinetics of molten aluminum on copper-coated ceramics , 2006 .

[47]  Jon J. Major,et al.  Groundwater Seepage Vectors and the Potential for Hillslope Failure and Debris Flow Mobilization , 1986 .

[48]  H. Suwa,et al.  Dissection of valleys by debris flows , 1980 .

[49]  L. Benda,et al.  Sediment routing by debris flow , 1987 .

[50]  S. Wood,et al.  Fire, storms, and erosional events in the Idaho batholith , 2001 .

[51]  S. Hsiau,et al.  Fluctuations and self-diffusion of sheared granular material flows , 1999 .

[52]  S. Wiederhorn,et al.  Effect of material parameters on the erosion resistance of brittle materials , 1983 .

[53]  E. Foufoula‐Georgiou,et al.  Channel network source representation using digital elevation models , 1993 .

[54]  D. Lague,et al.  Constraints on the long‐term colluvial erosion law by analyzing slope‐area relationships at various tectonic uplift rates in the Siwaliks Hills (Nepal) , 2003 .

[55]  S. Savage,et al.  Shear stresses developed during rapid shear of concentrated suspensions of large spherical particles between concentric cylinders , 1983, Journal of Fluid Mechanics.

[56]  L. Benda.  The influence of debris flows on channels and valley floors in the Oregon Coast Range, U.S.A. , 1990 .

[57]  T. Davies.  Debris-flow surges : experimental simulation , 1990 .

[58]  S. Cannon.  Debris-flow generation from recently burned watersheds , 2001 .

[59]  Burbank,et al.  Structural and topographic evolution of the central Transverse Ranges, California, from apatite fission‐track, (U–Th)/He and digital elevation model analyses , 2000 .

[60]  Measurement of debris flow and sediment-laden flow using a conveyor-belt flume in a laboratory , 1981 .

[61]  R. Webb,et al.  Cosmogenic 3He ages and frequency of late Holocene debris flows from Prospect Canyon, Grand Canyon, USA , 1999 .

[62]  S. Savage,et al.  The effects of an impact velocity dependent coefficient of restitution on stresses developed by sheared granular materials , 1986 .

[63]  R. Stephenson.  Flexural models of continental lithosphere based on the long‐term erosional decay of topography , 1984 .

[64]  H. J. R. Deketh,et al.  Towards the prediction of rock excavation machine performance , 1998 .

[65]  G. Tucker,et al.  Landscape response to tectonic forcing: Digital elevation model analysis of stream profiles in the Mendocino triple junction region, northern California , 2000 .

[66]  An Experimental Study of the Rapid Flow of Dry Cohesionless Metal Powders , 1986 .

[67]  Alberto Lamberti,et al.  Granular streams rheology and mechanics , 2000 .

[68]  W. Dietrich,et al.  Sediment and rock strength controls on river incision into bedrock , 2001 .

[69]  P. Wapner,et al.  Slurry erosion of polyphenylene sulfide-glass fiber composites , 1987 .

[70]  Kurosch Thuro,et al.  Roadheader Excavation Performance - Geological And Geotechnical Influences , 1999 .

[71]  R. Iverson,et al.  U. S. Geological Survey , 1967, Radiocarbon.

[72]  Richard M. Iverson,et al.  New views of granular mass flows , 2001 .

[73]  M. Stack,et al.  Impact angle effects on the transition boundaries of the aqueous erosion–corrosion map , 1999 .

[74]  S. Hsiau,et al.  Measurements of velocity fluctuations of granular materials in a shear cell , 1998 .

[75]  Garnett P. Williams,et al.  Erosional and Depositional Aspects of Hurricane Camille in Virginia, 1969 , 1973 .

[76]  André Vervoort,et al.  Correlation between dredgeability and mechanical properties of rock , 1997 .

[77]  V. S. Vutukuri,et al.  Handbook on mechanical properties of rocks. Testing techniques and results. Volume 1. Textbook : 200F, 30T, 260R. TRANS. TECH. PUBLICATIONS, V1, 1974, 300P , 1974 .

[78]  W. Dietrich,et al.  The importance of hollows in debris flow studies; Examples from Marin County, California , 1987 .

[79]  G. Wieczorek,et al.  Debris-flow hazards in the Blue Ridge of central Virginia , 2000 .

[80]  A. Evans,et al.  Fracture Mechanics of Ceramics , 1986 .

[81]  G. L. Sheldon,et al.  An investigation of impingement erosion using single particles , 1972 .