A major concern was that an eruption might cause the walls of Sherman Crater to collapse, sending lahars into Baker Lake reservoir and cause a wave to overtop, or significantly damage, the Upper Baker Dam. Either event would result in a large volume of water rushing into the Lake Shannon reservoir and potentially cause a surge of water over, or failure of, the Lower Baker Dam. Failure of the Lower Baker Dam would result in catastrophic flooding down the Skagit River with little to no warning. This was an especially worrying scenario for the town of Concrete, which lies at the foot of the Lower Baker Dam.