Blowout (geomorphology)

A blowout is a sandy depression in a sand dune ecosystem, hollowed out when wind removes sediment. Blowouts are commonly found on coasts and along the margins of arid areas. They tend to start where wind erodes a patch of bare sand on a dune that has been stabilised by vegetation, usually on the drier, more disturbed upper parts of the dune, and they generally do not form on actively moving dunes because the sand needs to be bound by plant roots. Most bare patches re-vegetate before they expand, but when conditions favour it the wind gouges the surface and creates a tunnelling effect that speeds the local airflow. The depression deepens until it reaches material that cannot be eroded or its shape limits it, and the sand carried out is dropped on the downwind side, where it can bury vegetation and enlarge the hollow, a process that helps create parabolic dunes. Plant cover decides whether blowouts form at all: a protective skin of roots and litter resists erosion, and pioneer species can halt a blowout.