Lecture 3 Sediment transport

Processes of transport (And a few examples)

Transport in fluids By settling: Stokes Law

Transport in fluids By settling: Stokes Law U = r 2 g  /18  U = settling velocity r = radius of particle g = gravitational acceleration  difference in density  viscosity

Transport in fluids By settling: Stokes Law U = r 2 g  /18  What will fall faster? Boulders or sand grains?

Transport in fluids By settling: Stokes Law U = r 2 g  /18  What will fall faster? Heavier grains or lighter grains?

Transport in fluids By settling: Stokes Law U = r 2 g  /18  What will fall faster? Grains in clear water or grains in turbid water?

Transport in fluids By settling: Stokes Law U = r 2 g  /18  What will fall faster? Clasts on Earth or clasts on Mars?

The effect of turbulence Multiple grains also slow settling, because they increase the effective viscosity

Transport in fluids By settling: Stokes Law By rolling, jumping and suspension

Whether or not movement occurs is a function of...

…density, mass, shape, size, flow velocity, and turbulence. Consider, for example, the influence of flow velocity

Shear of the fluid near the bed produces lift. If the lift forces are greater than the gravitational forces on the grain, the grain moves off the bed.

Fine sand ~ 1 cm/sec Coarse sand ~ 2 cm/sec Medium pebbles ~ 8 cm/sec

This only applies to silt-sized and larger particles. Why?

Bedload, suspended load. Rolling, saltation and suspension.

Transport environments Gravity-dominated –Rock falls, taluses

Transport environments Gravity-dominated –Rock falls, taluses Water-dominated –Rivers, lakes, oceans, estuaries

Transport environments Gravity-dominated –Rock falls, taluses Water-dominated Ice-dominated

Transport environments Gravity-dominated –Rock falls, taluses Water-dominated Ice-dominated Atmosphere-dominated

An example from the Mono Craters Pyroclastic fall deposits

An example from the Mono Craters Near-source (proximal)

With Stokes Law in mind, how might one explain these types of grading?

An example from the Mono Craters Far from source (distal)

Pyroclastic surge deposits