Dunes first begin their life as a stationary pile of sand that forms behind some type of vertical obstacle.
(Dunes; begin; their life; as a stationary pile of sand; T:first) (a stationary pile of sand; forms; L:behind some type of vertical obstacle)
Dunes a stationary pile of sand
begin forms
their life as a stationary pile of sand T:first
L:behind some type of vertical obstacle