Each summer in the mountains above Juneau, Alaska, meltwater from the massive Mendenhall Glacier flows into mountain lakes and into the Mendenhall River, which runs through town.

One of Alaska's most populated cities is bracing for potentially catastrophic flooding as a basin dammed within the Mendenhall Glacier has started to release water.

Mendenhall River crested at a record-setting 16.65 feet deep as of 7:15 a.m. Alaska time (12:15 Eastern), and began to empty, according to National Weather Service experts. The water level had fallen to about 8.