Flow, deformation, and transport - Physical Processes in Earth and Environmental Sciences - page 139

Upslope propagation of failure

Curvilinear failure plane

Shear mixing around flow front

Possible
aquaplaning

Weak layer/high pore pressure

Sediment slumps and slides

Free-shear layers

Separation zone,
turbulent mixing

Turbulent suspension eventually
overtakes or diverts from debris flow

Flow separation point

Debris flow with turbulent cap

Flow ceases when slope drops below critical
slope needed to exceed Bingham yield stres

Turbidity flow

Limited (<15%) resuspension
by turbulent “pick-up”
under head and body

Velocity of head, u h = 0.7 (g´h) 0.5

Fig. 4.64 Various possible flow transformations from subaqueous sediment slumps and slides via debris flows to turbidity flows.

denser and ambient fluid also takes place by entrainment
behind the head. Continued forward motion of the head at
constant velocity requires a transfer of denser fluid (buoy-
ancy flux) from the tail into the head (and thus for the tail to
move faster than the head) in order to compensate for
boundary friction, fluid mixing, and loss of denser fluid in

the head region. A steady state is brought about in flows
that have a near-constant input of dense solution with time.
In Nature, steady turbidity flows might occur over a
period of time as sediment-laden river water debouches
into a water body and travels along the bottom as a
continuous underflow. By way of contrast, surge-like