Week 5: Mass Transport Processes - Sediment Gravity Flows

Tuesday: Mass Transport Processes

  • Distinction between two major types of sediment transport processes:
    1. "Normal" traction transport: clear-water flows, in which shear stress is applied to sediment in the bed
    2. Mass-Transport processes: mass movements resulting from the weight of sediment; water is usually part of these types of movements, but the driving force is the weight of the sediment itself, not flowing water.

    Mass Transport Processes (Table 2.1) aredivided into:
    (1) Elastic Behavior: rockfall, slides and slumps;
    (2) Sediment Gravity Fows: have plastic and fluidal rheology (= focus for today)

  • Some Examples of mass-transport processes: slides, slumps, landslides, debris flows, avalanches, turbidity currents.
  • Why/Where do mass-transport "events" occur? Most of these are triggered by slope failures. Critical conditions for slope failure, a few factors such as water saturation, slope oversteepening, and E.Q. shaking.


  • Mass Flows typically evolve downslope, undergo "flow transformations":

    Example: slide ==> slump ==> debris flow ==> turbidity current (if subaqueous)

    Many/most flow transformations of this type result from incorporation of water into the flowing material, can also occur in subaerial settings (during floods, in streams, etc.)

  • Different types of flows, their physical behavior, main particle support mechanisms, and types of deposits (the product) produced by these processes.

    Today we focussed on processes and products of debris flows and turbidity currents.
    Processes     include material properties (plastic vs. fluidal), flow behavior (laminar vs. turbulent), and particle support mechanisms (matrix cohesive strength vs. turbulent suspension).
    Products     are sedimentary deposits that have distinctive grain size, sorting, textures, and sedimentary structures.

  • All summarized in Table 2.1 and Figures 2.6-2.8 AND all of Box 2.4 including figures.

    See also the nice Handout (Nemec, 1990) showing flow transformations in gravelly sediment gravity flows.

    We watched some cool Sediment Transport Movies that are posted online by Paul Heller (debris flows and turbidity currents) ... and photos of matrix-supported conglomerates and turbidites in the field.

    Here are a few examples from Field Photos

    Return to Lecture Outlines