Summit Lake outburst floods Salmon River; Hyder road at risk

The Salmon River near Hyder is rising after a glacier-dammed lake outburst from Summit Lake began Monday, threatening the road to Premier, Canada near mile point 9 along the Salmon River.

National Weather Service Juneau issued back-to-back special weather statements, one at 10:03 p.m. Monday and another at 5:38 a.m. Tuesday, confirming the outburst is underway. The river is expected to crest Wednesday or Thursday, but NWS said the total volume of water Summit Lake will release is unknown. "It is unknown how much water will be released from Summit Lake which results in large uncertainty on crest height and timing," the agency said.

The Road at Risk

NWS identified the road from Hyder to Premier, Canada as the potential impact area for this event, specifically near mile point 9 along the Salmon River.

NWS warned of debris in the floodwater and said the cold temperature of the water creates a high risk of hypothermia for anyone who enters it. The agency asked residents and travelers to report observed impacts directly to NWS Juneau.

A Known Hazard, Uncertain Scale

The Salmon Glacier and Summit Lake system near Hyder is a documented recurring outburst-flood hazard in Southeast Alaska, with mid-July drainage from this system a known seasonal pattern. A 2022 USGS analysis found that outburst floods in some glacierized watersheds are peaking faster and carrying greater infrastructure risk as glacier conditions change.

How high the Salmon River crests depends on how much water Summit Lake holds. That number is not yet known.