Ice dams are a common threat in the northern climates.  There are a few ways to deal with them.  However, one must understand how they are formed before they can be removed.

Ice dams form at the edge of the roof near the gutters.  In a situation where there is poor ventilation from the attic, warm air rises and melts the snow closest to the roof.  The water then travels to the bottom of the roof where it wants to run off, but cannot, either due to gutter blockage or excessive snow.   Eventually, the water turns to ice and the cycle continues.  The ice forces its way underneath the shingle.  If and when this ice melts, it will create a leak on the inside of the home

Try to keep as much snow off your roof as possible.  This obviously does not mean putting yourself in danger.  Research the various methods of removing snow from the roof, or call in the professionals.  If you do notice water damage in your home, it is best to have the roof or attic repaired in the spring, summer or fall months, to prevent the same problems from happening again.

Source:  http://ezinearticles.com/?Ice-Dams-That-Create-Home-Water-Damage&id=3371331