Dam Failure Lesson Learned: Natural dams can form quickly through processes such as landslides, avalanches, and river ice jams. In some cases, the formation of natural dams requires prompt intervention to protect people and property.

While the focus of dam safety is appropriately on manmade dams, practitioners need to be aware that nature also forms dams that can fail with devastating results. These dams can form quickly and form large dams through such processes as landslides, avalanches, glacial ice movement, and river ice jams. In some cases, a prompt intervention response is needed because the watercourse impounded by a natural dam can quickly become a lake and become a hazard. Dams formed from landslides, glacial ice, and neoglacial moraines are the natural dams that present the greatest threat to people and property¹. This lesson learned is to make the reader generally aware of the natural dams that have the most potential to become a risk. Specific geologic formation and failure mechanisms of natural dams can be found in the references.