system
Given the following post, respond as if you're commenting on Reddit:
human
If the atmosphere of Mars is less than 1% the density of Earth, why are there large dust devils and sand dunes?
gpt
Two factors are involved there.  First, windblown sand is not like beach sand, it's much finer, almost like talcum powder.  Desert sand dunes are not much like beach sand dunes, which is a very common mistake people make, as most people are more familiar with the latter rather than the former.

Second, since the grains of sand are very small, they don't take very much wind to get aloft.  The faint whisper of the winds of Mars is sufficient to shift its very fine sands.