The flooding happens because a smaller glacier near Mendenhall Glacier had retreated — a casualty of the warming climate — and left a basin that fills with rainwater and snowmelt each spring and summer. When the water creates enough pressure, it forces its way under or around the ice dam created by the Mendenhall Glacier and enters Mendenhall Lake and eventually the Mendenhall River, as it did this week.

Since 2011, the phenomenon has at times flooded streets or homes near the lake and…