why the wind erosion remain confined to the lower level of a rock
Answers
The first effect is the winnowing of light particles. Wind erosion is very selective, carrying the finest particles - particularly organic matter, clay and loam - many kilometres. The build-up of this alluvial matter stripped by the wind from the periglacial steppes gave rise to the fertile loess soils that cover large areas of Europe and North America, where highly productive farming has developed.
• The most spectacular forms are dunes - mounds of more or less sterile sand - which move as the wind takes them, even burying oases and ancient cities.
• Degradation of sedimentation crusts on the surface of stripped soils, or the weathering of rocks at their base where they are in contact with the soil (abrasion).
• Sheets of sand travelling close to the ground (30 to 50 metres) can degrade crops (particularly millet or cotton seedlings in semi-arid zones).
• Lastly, wind erosion reduces the capacity of the soil to store nutrients and water, thus making the environment drier.