What is a dune?

   A dune is a hill of sand. Dunes are found along shores of lakes and oceans and in sandy deserts. Some of the biggest dunes in the world are on the shores of Lake Michigan.
   Dunes are built by the wind. A small plant may start a dune. Wind carrying a load of sand strikes the little plant and drops part of its load. The sand forms a tiny hill in front of the plant. Now the wind strikes the tiny hill and drops more sand. Little by little the hill grows.
   In one way dunes are very different from other hills—they go traveling. The wind blows sand up one side of the hill and over the top. The sand rolls down on the other side. In this way the dune slowly moves. Sometimes a moving dune buries a forest. Sometimes it moves on past and leaves a forest graveyard behind it.
   There are many dunes that are no longer traveling. This is the story of almost every dune that has stopped moving: A newer dune first shut off much of the wind. Then small plants began to grow on the old dune. These plants helped protect the surface sand from the wind. Bigger plants could then grow and hold the dune in place. Some dunes have forests on them.