The glacier floods with water from melting ice have risen in the past few days as they flow through a river that runs through the capital of Alaska, without major damages reported, although authorities warned that the waters could remain high for several hours.
Some residents of Juneau in the flood-prone area heeded the warnings and evacuated after water began to escape from the dam around the Mendenhall Glacier on Tuesday.
By Wednesday morning, the city reported that water was accumulating on a handful of streets after seeping under the newly erected barriers designed to protect houses from the river, but no major damage was evident, even as the river rose to record levels.
The Mendenhall Glacier is about 19 kilometers (approximately 12 miles) from Juneau, home to 30,000 people, and is a popular tourist attraction due to its proximity to the capital of Alaska and easy access via hiking trails.
The houses in the outskirts of the city are just a few kilometers from Mendenhall Lake, which lies beneath the glacier, with many facing the Mendenhall River, where the glacial runoff is flowing.
The river reached higher levels at 6 a.m. local time, already surpassing last year’s record flooding level of nearly 5 meters (16 feet), and it was expected to peak at 8 a.m. before the waters receded by Thursday, according to the National Weather Service. Preliminary measurements indicated that a record set last year was broken.
Bowl flooding is an annual issue
Bowl flooding has become an annual concern since 2011, and in recent years has destroyed homes and flooded hundreds of households.
Government agencies installed temporary barriers this year hoping to protect hundreds of homes from widespread damage.
The flooding occurs because a smaller glacier near the Mendenhall Glacier collapsed — a victim of warm weather — leaving a bowl that fills with rainwater and melting ice every spring and summer.
When the water creates enough pressure, it finds its way under or around the ice dam created by the Mendenhall Glacier, enters Mendenhall Lake, and ultimately flows through the Mendenhall River, as it did on Tuesday.
Before the bowl started to overflow, the water level was rising rapidly — up to 1.20 meters (4 feet) per day during particularly sunny or rainy days, according to the National Weather Service.
The city experienced successive years of record floods in 2023 and 2024 — with the river reaching 4.9 meters (16 feet) last August, about 30 centimeters (1 foot) above the previous record set a year earlier — and the floods extended further into the Mendenhall Valley. This year’s flood was predicted to reach between 4.9 and 5.1 meters (16.3 and 16.8 feet).
Last year, nearly 300 residences were damaged.
A large discharge can release about 15 billion gallons of water, according to the University of Alaska Southeast and the Alaska Climate Adaptation Science Center.
That’s equivalent to nearly 23,000 Olympic-size pools. During last year’s flood, the flow rate in the mighty Mendenhall River was approximately half that of Niagara Falls, say the researchers.
Temporary dike installed to prevent glacier flooding
The city officials responded to homeowners’ concerns this year by working with state, federal, and tribal entities to install a temporary dike along approximately 4 kilometers (2.5 miles) of riverbank in an attempt to protect against widespread flooding.
The 10,000 Hesco barriers are essentially giant sandbags meant to fully protect over 460 properties during a 5.5-meter (18-foot) flood event, stated emergency manager Ryan O’Shaughnessy.
The Army Corps of Engineers at the start of what is expected to be a multi-year process to study the conditions in the region and explore options for a more permanent solution, such as a dike. The timeline has angered some residents who find it unreasonable.
Glacial runoff floods are expected to continue as the Mendenhall Glacier acts as an ice dam to seal the bowl, a process that could span another 25 to 60 years, according to university and science center researchers.
