Juneau, Alaska – Water has begun to be released from the ice dam of Suicide Basin, a glacial lake formed by the Mendenhall Glacier. This event is expected to cause significant flooding along the Mendenhall River, with water levels anticipated to peak between late Tuesday and Wednesday. Residents in vulnerable areas have been advised to move to higher ground as a precautionary measure.
This phenomenon, known as a glacial outburst flood or jökulhlaup, occurs when the pressure of accumulated water exceeds the glacier's containment capacity. The release of water into Mendenhall Lake and the river below has been a recurring concern for the Juneau community since 2011, with past events causing considerable property damage. In response to the current threat, a temporary levee system utilizing Hesco barriers, a military-grade flood defense system, has been erected along the riverbanks. This measure is designed to protect numerous properties and mitigate flood levels, aiming to match those experienced last year. The Mendenhall River's water level is closely monitored, with a major flood stage typically set at 14 feet. Current forecasts suggest the river could crest at approximately 16.6 feet, potentially surpassing the record set in August 2024, when the river reached 15.99 feet.
The Mendenhall Glacier, a prominent natural feature and tourist attraction in Southeast Alaska, serves as a natural dam for Suicide Basin. This basin collects rainwater and snowmelt throughout the spring and summer. As the glacier recedes due to climate change, the capacity of Suicide Basin to hold water increases, leading to more potent flood events. The first recorded jökulhlaup on the Mendenhall River occurred in July 2011. Officials have been actively preparing for this year's event, with the U.S. Army Corps of Engineers assisting in the deployment of the Hesco barriers. These barriers are intended to fortify riverbanks and redirect water. While these measures are designed to withstand floods up to 17 feet, their performance beyond that threshold remains uncertain. The state of Alaska has issued a disaster declaration to proactively position resources and personnel to support local efforts in safeguarding lives and essential services. The community is advised to stay informed through official channels and heed all evacuation warnings.