Blowout (geology)

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

Blowouts occur in partially vegetated dunefields including continental dunes as well as coastal dunes. In either case, a blowout forms when a patch of protective vegetation is lost, allowing strong winds to "blow out" sand and form a depression. Although they generally remain small, blowouts can expand to kilometers in size and up to around 70m in depth.

Causes of vegetation loss include extended droughts, fire (natural and anthropogenic) or, in extreme cases, trampling by humans, cattle, horses, etc. Fire is the most common cause, however. In time, succession will begin again as suitable seeds are blown in and pioneers become re-established.

Coastal sand dunes are found just inland from a beach, and are formed as the wind blows dry sand inland beyond the beach. It follows that this can only happen when there is an area of reasonably flat land inland from the beach. In time, this rather inhospitable surface will be colonised by pioneer species. These species (e.g. marram grass) will stabilise the dunes and prevent them moving any more. The process of plant succession will eventually see these dunes converted to woodland (depending on the climate) and a mature soil will have formed.

Blowouts provide an important habitat for flora and fauna.