Why do ice jams often form where a river slope becomes gentler?

Ice jams often form where a river's slope changes from steeper to milder because the river's capacity to transport ice is reduced in these areas.12

When moving ice—which has been broken up and transported downstream by increased flow—reaches a section of the river with a gentler slope, the river's ability to carry that volume of ice decreases. If the quantity of ice exceeds the river's transport capacity at that point, the ice accumulates, creating an ice jam. These jams can also occur when moving ice encounters an intact ice cover, such as in a large pool or at the point where a river flows into a lake.12

Such blockages are significant because they can raise water levels, potentially causing flooding, and may lead to structural damage if the ice collides with bridges or other infrastructure.12