Strange Patterns

Melting Ice on Mars

I found this pattern of melting ice on the Martian pole strange. NASA explains the triangular spikes as being caused by wind erosion of the ice, but it seems wind erosion would not cause such sharp spikes. I would expect a more irregular pattern from wind erosion, plus we know that with Mars current thin atmosphere wind is not a very strong force. It seems more likely that the effect results from differing heat absorption near the surface, but what is causing this?