Patterns of wind flow and aeolian deposition on a parabolic dune on the southeastern shore of Lake Michigan

Sand deposition and patterns of wind flow were studied on Green Mountain Beach (GMB) dune, a large Lake Michigan coastal dune that is transitional between a trough blowout and a fully-developed parabolic dune. Deposition pins were used to study the amount and pattern of aeolian sand deposition on the lee slopes of GMB dune over 20 months. In the late fall and winter, sand supported by ice between the grains accumulated on the upper- to mid-slopes, and became over-steepened (38°). During measurement periods containing two major storms with wind gusts up to 25 m/s, a total of 44% of the deposition on the lee slope occurred, compared to an average of 9% for comparable time periods between storms. Sand was delivered by mass movement to the lower slopes during the spring thaw. Very little sand was deposited on lee slopes during the summer. Maximum sand deposition occurred near the dune axis, oriented southwest–northeast, and then decreased rapidly along the limbs. Maximum sand transport and dune migration were oriented towards the northeast despite the dominant regional winds during the fall and winter being from the west and northwest. Arrays of anemometers and wind vanes were used to study airflow patterns within GMB dune on five different days. These studies indicate that steering of winds in the deflation area of the dune may be responsible for the northeasterly sediment transport. They also suggest, however, that the ability of the dune to steer winds, and thus, control the direction of sand transport and deposition, decreases when the angle between the oncoming winds and the dune axis is too great.