Question

Vast tracts of moving sand​

Answer 1

Explanation:

Dunes might look like a little more than a pile of sand, but they are constantly changing. They form when water and air pile loose sand against a barrier, such as foothills or tall mountains. Dunes grow, shrink, change shape, and move positions as water and air move around them. Some of the national parks contain large expanses of dunes, including vast tracts of white sand dunes and the tallest dunes in North America. Find out more about the science and stories behind sand dunes and their diverse ecosystems.