Massive amounts of rain and snowmelt from Alaska’s Mendenhall Glacier have begun to spill over, and authorities urged residents in parts of Juneau to evacuate Tuesday because of possible record floodwaters downstream.
In recent days, authorities have been warning people in the flood zone to be prepared to evacuate.
On Tuesday morning they confirmed that water had begun to overflow from under the ice dam and flow downstream, with flooding expected from Tuesday evening into Wednesday.
Flooding in the river basin has become an annual problem, with hundreds of homes washed away and inundated in recent years.
This year, government agencies introduced a temporary levy in hopes of preventing widespread damage.
“Based on all the information we have, this is going to be a new record,” National Weather Service meteorologist Nicole Ferrin said at a news conference Tuesday.
The Mendenhall Glacier, a thinning and retreating glacier that is a major tourist attraction in southeast Alaska, dams Suicide Lake, which fills with rain and snowmelt each spring and summer.
The basin itself remained after the retreat of a smaller glacier located nearby.
When the water pressure in the basin reaches a sufficient level, it is forced under or around the ice dam, entering Mendenhall Lake and eventually the Mendenhall River.
Before the pool reached its limit and began overflowing over the weekend, water levels were rising rapidly — up to 1.22 meters per day on particularly sunny or rainy days, according to the National Weather Service.
The threat of so-called glacier outburst flooding has plagued parts of Juneau since 2011, with some years seeing limited flooding of streets or properties near a lake or river.
However, 2023 and 2024 marked two consecutive years of record flooding: last August, the river rose 17 feet (4.9 m) – 1 foot (30 cm) above the previous record set the year before – and flooding extended further into the Mendenhall Valley.
This year’s flood water level is predicted to be between 4.96 and 5.12 m.
Last year, about 300 residential buildings were damaged.
A major breach could release about 15 billion gallons of water, according to the University of Alaska Southeast and Alaska State University’s Climate Adaptation Science Center.
That’s the equivalent of nearly 23,000 Olympic swimming pools. During last year’s flood, the Mendenhall River’s raging flow was about half that of Niagara Falls, researchers said.
This year, city officials responded to property owners’ concerns by working with state, federal and tribal agencies to install a temporary levee along about 2.5 miles of the riverbank in an attempt to protect against major flooding.
Installing about 10,000 4-foot-tall barriers will protect more than 460 properties from flooding similar to last year, said Nate Ramsey, deputy director of the city’s Department of Engineering and Public Works.
The U.S. Army Corps of Engineers is at the beginning of what is expected to be a multi-year process of studying conditions in the region and exploring options for a longer-term solution.
These deadlines have caused outrage among some residents, who consider them unreasonable.
Flash floods are expected to continue as long as the Mendenhall Glacier acts as an ice dam blocking the basin, which could be another 25 to 60 years, according to researchers at the university and the center.
Sourse: breakingnews.ie