The of a dune is characterized by a decrease in energy and sand avalanches, which occur due to oversteepening

Dunes move over time with the wind as sand grains climb the windward slope of the dune until they are pushed it the leeward side where they slip down the lee slope. And it is called Leeward Side. leeward sides of the mountains has lost much of its moisture making these regions much drier. 

because they are eaten by the frog and the frog getseaten by the snake and the snake by the eagle

condensation. good luck!