Ice dams form through a specific and somewhat counterintuitive process: heat escaping from your attic warms the roof deck enough to melt snow near the ridge, that meltwater runs down to the colder eaves and refreezes, and over successive freeze-thaw cycles, a ridge of ice builds up right at the roof edge — often right where your gutters are.
Once that ice dam forms, additional meltwater has nowhere to go and can back up under your shingles, leading to leaks well above where the actual ice is sitting. The weight of the ice itself can also pull gutters away from the fascia or crush them outright.
The real fix isn’t heated cables or chipping ice away, though those can help in the short term — it’s addressing the root cause, which is usually inadequate attic insulation or ventilation letting too much heat escape into the roof deck. If ice dams have been a recurring problem at your home, it’s worth having both your attic ventilation and your gutters evaluated together, since fixing one without the other often doesn’t solve the underlying issue.