What is "ice dam"

n. 1 an obstruction to the flow of a river caused by the flow of a glacier 2 (context roofing English) 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.

An ice dam occurs when water builds up behind a blockage of ice. Ice dams form either when glacier blocks a river and forms a lake or when ice chunks in a river are blocked by something and build up to form a dam, often called an ice jam. Glacial ice dams have historically resulted in massive outburst floods. River ice jams can cause flooding upstream during the jam, flooding downstream when the jam releases, and damage from the ice itself on structures and ships in or near the river. Ice jams on a lake or ocean occur during the spring break-up if wind driven ice piles up along a shoreline.

An ice dam is an ice build-up on roofs of buildings which may cause water damage to the building and contents if the water leaks through the roof.