Glacial outburst floods aren't a new phenomenon in Alaska, but climate change is scrambling the geography of risk.

Residents in some parts of Juneau prepared to evacuate ahead of what could be a record surge of flooding as rainwater and snowmelt in a huge basin dammed by Alaska’s Mendenhall Glacier started to flow downstream toward the capital city.

Because the flooding has been a growing concern, city officials have installed emergency flood barriers along several miles of riverbanks.