ice dam

Short definition from Wiktionary

Noun

1. 1
   An obstruction to the flow of a river caused by the flow of a glacier across its course.
2. 2
   An obstruction to the flow of a river caused by the concatenation of surface ice into a ridge that rises above and sinks below the surface causing a blockage, occurring frequently during spring breakup season.
3. 3
   A mass of ice formed at the transition from a warm to a cold roof surface, frequently formed by refreezing meltwater at the overhang of a steep roof, causing ice and water to back up under roofing materials.
4. 4
   Ellipsis of ice dam membrane.