Ice dam formation is caused when melting snow runs down the roof and then refreezes at the roof edge. 

The water runs down the roof slope underneath the blanket of snow and then refreezes into a band of ice at the roof edge creating a "dam". Additional snowmelt can then pool against the dam and leak into the home through the roofing shingles or metal trim. Ice dams can actually form with as little as 1 or 2 inches of snow accumulation given the right weather circumstances.  

Tulsa Roofing Etc can remove the ice dam to stop the roof from leaking and then come back when the rest of your roof is dry and install metal pans, and or moisture guard in these problematic areas to make sure that the next time the snow falls you are covered. ice dams can only be prevented when snow is taken into consideration when installing your new roofing system.