Lecture 3 Sediment transport. Processes of transport (And a few examples)

Lecture 3

Sediment transport

Processes of transport

(And a few examples)

Transport in fluids

• By settling: Stokes Law

Transport in fluids


U = r2g/18

U = settling velocity

r = radius of particle

g = gravitational acceleration

difference in density

viscosity

Transport in fluids


U = r2g/18

What will fall faster?

Boulders or sand grains?

Transport in fluids


U = r2g/18


Heavier grains or lighter grains?

Transport in fluids


U = r2g/18


Grains in clear water or grains in turbid water?

Transport in fluids


U = r2g/18


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 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/secCoarse 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



• Water-dominated– Rivers, lakes, oceans, estuaries



• Water-dominated

• Ice-dominated



• Water-dominated

• Ice-dominated

• Atmosphere-dominated

An example from the Mono Craters

Pyroclastic fall deposits


Near-source (proximal)

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


Far from source (distal)

Pyroclastic surge deposits

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Lecture 3 Sediment transport. Processes of transport (And a few examples)