Suspension (geology)
In sedimentology, suspension is a type of sediment transport. The transported material is also referred to as floating cargo . Suspension can take place in various transport media.
Suspension by water
The first transport medium of the suspension is water. The sediments that are transported in or by rivers can either be transported rolling or jumping on the river bed (debris load, soil load) or as suspended load (suspension). How the material is transported depends primarily on the flow speed and grain size of the transported material, see fluvial sediment .
Suspension by wind
However, the term suspension can also mean the transport of material by wind. The loose material is lifted from the ground by turbulence (eddies in the air flow) and transported with the wind. The type of transport is also dependent on the grain size and speed of the flowing medium - here the wind speed.
If the specific rate of descent of the particles is less than the speed of thrust, particles will be carried in suspension with the wind (often in dust storms ) and will not sink back to the ground. In general, particles with a diameter between 20 and 70 µm can travel many kilometers ( short-term suspension ). Fine dust (<20 µm) can linger in the atmosphere for long periods of time and cover very long distances ( long-term suspension ).
Coarser material is only moved by jumping in saltation and quickly falls back to the ground after a few meters in the event of wind erosion. If the particles hit other particles on landing, part of it is transferred to them and they move forward crawling. This secondary mode of locomotion is called reptation .
Suspension plays a very important role, especially in the spread of loess. Here the loess is deposited directly from the suspension when the wind speed drops. The flat subsidence of the "dust clouds" creates relief-compensating ceilings. If it is accumulated from the saltation, dunes tend to form, as is the case with sand.
literature
- Harald Zepp : Geomorphology. An Introduction ( UTB ; Vol. 2164). 3rd, revised edition. Schöningh, Paderborn 2004, p. 138 ff., P. 171 ff., ISBN 3-8252-2164-4 .
Individual evidence
- ↑ a b after Pye (1987) in Jürgen Schultz (2000): Handbook of Eco Zones . Ulmer Verlag, Stuttgart 2000, p. 371, ISBN 3-8001-2752-0 .