Even when moisture content is fractional, particles may be bound together by surface tension in the meniscuses between them. This is dependent upon particle size and is affected by a whole range of other possible variables, such as organic content, clay mineralogy, etc. However, generally speaking, with particles of a given size, the required threshold velocities increase with increasing moisture contents. The effectiveness of plant cover depends on cover height, cover form, cover density and presence of plant litter. The work of wind produces both depositional and erosional landforms.
Dunes are the obvious depositional forms and range enormously in form, size and composition.
They may be stable, anchored or mobile and the occurrence of each type depends primarily upon wind regime, sediment supply, vegetation cover and moisture. Australia is particularly noted for its longitudinal dunes and lunettes. The latter are formed by deflation of lake bed sediments, and form distinctive crescentic dunes on the lee side of lakes. The major depositional and erosional features of Australia s arid zone will be covered in the next lecture.