Coastal and Oceanic Landform (21.Dune System)

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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.

• 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.

  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)

Foredunes

• 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;

                                                  blowouts

                                                  parabolic dunes

                                                 transgressive dunefields

Blowouts

• 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 .