Sand dunes are accumulations of windblown sand piled up in mounds or ridges. Cryoconite, powdery windblown dust containing soot, sometimes reduces albedo on glaciers and ice sheets. Deposits of this windblown silt are known as loess. The ridge is primarily composed of the windblown glacially derived sediment known as loess. Stabilising dunes can help protect beaches by catching windblown sand, increasing natural beach formation. Windblown salt dust from exposed playas may affect upland soils and vegetation. Sediment and debris from the Okavango River and windblown sand were gradually filling the lake. Windblown sand erodes glass in dry climates, protective layers add expenses. Fences can allow sand traps to create blowouts and increase windblown sand capture. A layer of windblown sand transformed the monument into a simple hillock. He suggested windblown sand or dust as the cause of the clouds. Up until the 1940s, Point Dume was a windblown, treeless bluff covered by native chaparral. His hair was windblown and full of raindrops. According to the United States Geological Survey, Brownsville's soils are primarily alluvium and windblown deposits. The materials were designed for resistance to windblown dust, sand and chemical agents.