Icicles: decorative in concept but a real problem for the homeowner.
They form when snow melt on the roofs meets cold air. Gutters don't work for icy water, and they may even be brought down by the weight.
Even more alarming is that water pools behind the ice dam and will begin seeping into the house, becoming a steady flow that can only be stopped if the dam is removed or there is a protracted thaw. People try using heated wires with limited success.
Trying to remove the ice is tricky and dangerous. It is easy to damage the roof doing it. And you can break your neck.
The culprits are heated top floors that are poorly insulated, and shallow eaves.
A cold attic with an insulated floor works great. So do deep eaves that let the water travel away from the house. Also steep slate roofs.
Living in the cold north is interesting.