During winter, temperatures drop so much that CO2 freezes
Nothing really happens on Mars, it's just one big desert. It seems that anything interesting there happened a long time ago. But it's not all dead, some spectacular phenomena can still be spotted.NASA has put together a video showing some of the things happening at Mars' frozen poles where water and carbon dioxide ice forms.
When this ice thaws, the carbon dioxide builds up as a gas beneath eventually exploding bringing up large quantities of dark Martian sand with it.
The CO2 ice, or dry ice, forms during the winter when temperatures drop so much that the gas becomes a solid. In the spring, the dry ice sublimates, it goes straight from solid to gas.
This phenomenon leads to some very interesting and quite alien looking landscape, a very dynamic one as well, something scientists didn't really believe they'd find on Mars.