Question

A sand dune at the beach is not a stable community. Use your knowledge to explain why?

Answer 1

Answer:

Explanation:

The size and morphology of coastal dunes is dependent on the complex interaction between controlling winds, sediment supply, and the geomorphology of the nearshore and beach environment. At the most basic level, dunes can be divided into those that form from the direct supply of sediment from the beach face (primary dunes), and those that form from the subsequent modification of primary dunes (secondary dunes).

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Classification of Coastal Dunes

Depending on the characteristics and availability of the sediment supply, dominant wind velocity and direction, moisture and vegetation present, and the geomorphology of the nearshore and beach face, dunes of various size and morphology are formed (for processes on aeolian transports see Sloss et al. this issue). Sand deposition, accretion, and erosion within the coastal environment result in the development of a variety of dune morphologies; however, a general classification into primary and secondary dunes can be made (Davis 1980, Masselink & Hughes 2003). Primary dunes are composed of sand blown directly from the beach face (active beach), whereas secondary dunes develop following the subsequent modification of primary dunes.

Primary Dunes

Davies (1980) defined "primary dunes" as dunes with a sand supply derived primarily from the beach and "impeded primary" dunes as those in which vegetation plays a major role (i.e., impedes downwind transport) in the development of the dune. They are the dunes closest to the shoreline, dynamically linked to beach processes, and significantly influenced by wave action as both a constructional and erosional force.

Foredunes

Foredunes develop at the rear of the backshore environments (landward of the active beach) and generally comprise shore-parallel, convex, symmetrical to asymmetrical dune ridges. The morphology of foredunes is varied but they can be classified into three main types: incipient foredunes, established foredunes, and relict foredunes (Short & Hesp 1982, Hesp 2002).

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