SAND MOVEMENT

I have discussed previously that desert sand moves by prevailing winds. But there are several ways in which they can move.

Sand particles can be carried by either:

Types of sand movement

Creep – These particles are too heavy to be picked up and moved however they can be slowly rolled by the wind or knocked along the grounds surface when other smaller particles collide with them through saltation.

Saltation – This is the picking up and movement of large particles from the grounds surface. As the winds carry the particles, they pick up velocity causing them to bounce along the ground. This bouncing process can heavily erode surfaces.

Suspension – Where particles are held in the air suspended by upward air currents which are then carried by winds.

Beach dunes

Okay slightly off-topic, beach dunes, also knows as coastal sand dunes, are formed by materials being blown in from the coast over the land. Sand is moved inland via saltation and air pressure between the warm land and colder sea.

I am not sure to what extent coastal dunes relate to desertification processes, however I came across coastal dunes when exploring the different types of dune formations and thought I’d make reference to them as I vaguely remember learning about them.

Unlike desert dunes, which comprise of little or no vegetation, coastal dunes can enhance vegetation growth. There are several sequences for the development of these particular dunes:

• At the back of the beach, sand can become trapped by rocks, seaweed and driftwood. Vegetation struggles to grow here however the little vegetation that does grow are referred to as pioneers e.g. sea rocket and saltwort.
• The development of the first dunes are known as embryo dunes. These dunes become stable by the growth (colonisation) of grasses e.g. sea couch, lyme and marram.



Coastal dune transect

• Embryo dunes can raise in height forming foredunes. These foredunes are mobile and can move up the beaches creating a main ridge (yellow dune), fixed dunes (grey dunes), dune heaths and mature dunes which all support a range of vegetation (see diagram). For more information on these types of dunes, the types of vegetation they support and the processes involved see:

http://www.s-cool.co.uk/a-level/geography/coastal-processes/revise-it/coastal-deposition

http://www.seftoncoast.org.uk/shore_featuresanddune.html

http://www.geography-site.co.uk/pages/physical/coastal/dunes.html

I do believe, however, that I have gone way off topic of ‘desertification’ and have been pulled into coastal environments, which is not an area that is classified under extreme landscapes. Going off topic is an easy thing to do, especially when in the classroom. I may return to coastal landscapes, their processes and features in later posts. For now it is only important that students are aware of the types of sand movement and are able to define each process.

Links:

http://milford.nserl.purdue.edu/weppdocs/overview/wndersn.html

http://geography.howstuffworks.com/terms-and-associations/sand-dune1.htm