Coastal and Oceanic Landform (21.Dune System)

                                                                                                       Back to Coastal and Oceanic Landform

The size and morphology of coastal dunes is dependent on the complex interaction between controlling winds, sediment supply, and the geomorphology of the near shore and beach environment.

  •   Dunes can be divided into the beach face (primary dunes)
  •  Form from the subsequent modification of primary dunes (secondary dunes).

Incipient foredune forming in Ipomoea plants and grasses, Yucatan coast, Mexico.
Incipient foredune forming in Ipomoea plants and grasses, Yucatan coast, Mexico.

  • There are 2 broad Zones within dune system;

                              1.The interdune
                              2.The backdune. 

  • Primary physical processes produce different zones 

                               1.The degree of exposure to / protection from on-shore winds.
                                    Dgree of sand stabilization

                              2.Soil moisture.

Classification of Coastal Dunes

Established foredune in southern Brazil.
Established foredune in southern Brazil.

  The foredune-:
                                  Most exposed to onshore winds& salt spray .
                                  It is dominated by Ammophila breviligulata (beach grass),other species. 

 The interdune-:
                                  Dominated by a combination of beach grass.
                                  Broader diversity of other species.

  The backdune-:More protected portions of the dune
                                   Characterized by;
                                                                       maritime (“sunken”) forests
                                                                       shrub thickets
                                                                       interdunal swales.


Primary Dunes

  • primarily from the beach.
  • "impeded primary" dunes plays a major role.
  • They are closest to the shoreline.
  • Dynamically linked to beach processes.
  • Significantly influenced by wave action(constructional & erosional force)


  • Develop at the backshore environments
  • Comprise shore-parallel convex
  • Symmetrical to asymmetrical dune ridges
  • Classified into 3 main types: 
                                      1.incipient foredunes
                                      2.established foredunes
                                      3.relict foredunes

Secondary Dunes

  • Result of the subsequent modification of the "primary dune".
  • Continued aeolian processes.
  • Generally located further inland.
  • Separated from nearshore processes.
  • Secondary dunes include;
                                                  parabolic dunes
                                                 transgressive dunefields


  • Commonly occur  foredune.
  • Older vegetated dunes.
  • Erosional dune landforms.
  • There  are typically trough-, bowl-, or saucer-shaped depressions.
  • Formed by wind erosion of a pre-existing sandy substrate.

Parabolic dunes

  • Transport of sand.
  • Blowouts development of parabolic dunes.
  •  Consist of  depositional lobe with two trailing arms.
  • Enclose a deflation basin.
  •  This produces a characteristic U-shape .

No comments:

Post a Comment