Further on the infrared observations of the "fans" seen on the
surface in the vicinity of the spiders appears here:

Carbon-Dioxide Frost Settling from Seasonal Outbursts on Mars (Movie).
http://mars.jpl.nasa.gov/mro/gallery/video/index.html#CarbonDioxideFrost

This page shows both visible light and infrared images of the fans
due to venting gas. The conclusion presented here is that the fans are
due to CO2 gas release because of the infrared signatures. However, it
is notable that there is quite a bit of evidence in the infrared of
water ice in the images as well. Then the infrared images as well are
still consistent with possibility of dissolving CO2-water clathrates.

Bob Clark