Imminent “glacial outburst” flooding threat prompts disaster declaration in Alaska

Alaska Gov. Mike Dunleavy issued a state disaster declaration Monday as a result of what he called the “imminent threat of catastrophic flooding from a glacier lake outburst flood (GLOF)” in the Juneau area. It would mark the third straight year of serious glacier-related flooding in Juneau, the state capital, in extreme southeastern Alaska.

The flooding would be associated with Suicide Basin, a side basin of the Mendenhall Glacier, Dunleavy said.

“Hydrologic monitoring by the National Weather Service (NWS) and U.S. Geological Survey (USGS) confirms that the volume of water currently impounded in Suicide Basin has reached or exceeded levels observed during prior flood-of-record events,” he warned in a statement. “A release is expected at any time. Flooding is likely to affect the Mendenhall River and surrounding neighborhoods in the Mendenhall Valley.”

The National Weather Service Juneau office said, “The Basin is full and continues to over-top. … As of 10 p.m. Monday, the release has NOT begun, but could happen at any point this week.”

The declaration follows joint local disaster declarations and requests for assistance from the city and borough of Juneau and two local Indian tribes, Dunleavy noted.

A GLOF a year ago caused widespread damage to homes, public infrastructure and utilities and prompted state and federal disaster declarations.

Video posted on social media two years ago showed towering trees behind a home falling into the rushing Mendenhall River as the water ate away at the bank. Eventually the home, teetering at the edge, also collapsed into the river.

To try to curb the impact of future flooding, Juneau and the Army Corps of Engineers have installed more than two miles of flood control barriers along the river.