Blowout (geology)

Blowouts are sandy depressions in a sand dune ecosystem (psammosere) caused by the removal of sediments by wind.

Commonly found in coastal settings and arid margins, blowouts tend to form when wind erodes into patches of bare sand on stabilized vegetative dunes. Generally, blowouts don’t form on actively flowing dunes due to the fact that they need to be bound by some extent, such as plant roots. These depressions usually start on the higher parts of the stabilized dunes on the account that desiccation and disturbances are more considerable which allows for greater surface drag and sediment entrainment when sand is bare. Most of the time, exposures become quickly re-vegetative before they could become blowouts and expand; however, when the opportunities are given, wind erosion can lower the exposure surface and create a tunneling affect, which increases the wind speed. The depression may continue until it hits a non-erodible substrate or morphology limits it. The eroded substances climbs the steep slopes of the depression and become deposited on the downwind side of the blowout which can form a dune that covers vegetation and lead to a larger area of depression; a process that helps create parabolic dunes.

Although there is a wide variety of vegetation that live in dune environments around the world, most plant species play a key role in determining whether blowouts will form or not by the result of how strong their protective skins can suppress erosion and how capable some pioneer species can repress further erosion if a dune becomes exposed.

Protective Skin

In the first case, the primary objective for the protective skin is to resist disturbances that will form open exposures and create blowouts. To prevent erosion, vegetation helps reduce shear stress by covering the surface and mechanically binding soil together. The protective skin is composed of vegetation that is above and below ground surface and decomposing plant liter. Additionally, the protective skin can also be composed of a wide variety of species that could constitute environments like grasslands and forest. However, if the climate changes, it can directly influence the health of the vegetation, which can make the skin fragile; nevertheless, the rate of change may take some time and may be different for stabilized dunes in different environments.

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