Sands of Time Title
This site provides detailed information on the sand dunes of the Sefton coast in North West England
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Blowouts
 

Vegetation plays a major role in stabilising the surface of the dune sand, developing root systems in the unconsolidated substrate, creating a layer of calm air immediately above the surface and adding organic matter which will also help to hold the sand together. If the vegetation is removed (for example by rabbit burrowing) this protection is gone. Strong winds can then pick up the sand and blow it elsewhere. A 'hole' is created in the surface of the dunes called a blowout.

 
A Small Blowout
A Small blowout
 

Formation of blowouts is an entirely natural process in the dunes. The very highly specialised plants of the early stages of dune succession (such as Marram) are very susceptible to damage and strong winds are experienced at the coast.

The sand surface of the blowout may eventually be recolonised by plants and 'heal' over. Sand Sedge Carex arenaria is well adapted to do this by sending underground rhizomes across the sand just below the surface, with shoots growing upwards to the surface at regular intervals.

 
Sand Sedge recolonising a Blowout
Sand Sedge re-colonising a blowout
 

The blowout may continue to increase to an extremely large size. There is an enormous blowout on Ravenmeols Local Nature Reserve called the Devil's Hole.

 
Devils Hole on Ravenmeols
A large blowout called Devil’s Hole on Ravenmeols dunes (1993).
 

If the surface is eroded down to the level of the water table wet sand will be exposed. The wind cannot pick up wet sand as the water holds the sand grains together and the hollow will not become any deeper. This creation of a surface of wet sand is how a secondary dune slack is formed.

 
Blowout and erosion down to wet sand
Blowout and erosion down to wet sand at the water table
 

The sand removed by the wind is usually deposited on the lee side of the blowout where it may cover the vegetation.

 
Sand deposited on lee side of Blowout
Sand deposited on vegetation on the lee side of blowout
 

Blowouts are most likely to occur near to the coast where there is less shelter from the strong onshore winds and the specialised vegetation at the early stages of succession is more fragile. Vegetation with a complete ground cover, high biomass and a well developed organic soil horizon is far less susceptible to damage and erosion.

 

 

For more information about this project email dunes@hope.ac.uk at Liverpool Hope University.
  Go to the site of Liverpool Hope University    

Liverpool Hope University worked with English Nature and the
Sefton Coast Partnership to implement the Sands of Time project.