In this screenshot from a video shared Monday by Capital City Fire/Rescue, the waters of Suicide Basin have topped the low point in the dam holding the reservoir and are beginning to flow downhill. (Screenshot)

In this screenshot from a video shared Monday by Capital City Fire/Rescue, the waters of Suicide Basin have topped the low point in the dam holding the reservoir and are beginning to flow downhill. (Screenshot)

Suicide Basin begins releasing water, but flooding risk unknown

Mendenhall Lake levels are declining, not rising

Suicide Basin began its long-awaited release of water late Monday, but there are no signs of incipient flooding along the banks of the Mendenhall River or Mendenhall Lake.

In fact, water levels within the lake and river system dropped Monday and Tuesday following the end of weekend rainfall.

“That’s telling us there is not that much inflow,” said Aaron Jacobs, a hydrologist with the National Weather Service in Juneau. “We’re not putting out any advisories or warnings or watch statements yet because we’re still seeing how this is going to evolve.”

For the past eight years, Suicide Basin, in a side lobe of the Mendenhall Glacier, has been collecting and releasing water with seasonal regularity, occasionally causing minor flooding along the lake and river that share the glacier’s name.

The worst flooding was in 2016, and the scientists who monitor the basin have previously told the Empire that water levels within its reservoir are at or above 2016 levels.

It’s not yet clear whether that means the Valley should expect another summer of high water.

Since it began causing regular floods, the basin has released its water through channels beneath the glacier. Those channels are normally blocked by ice, but when the water pressure within the basin exceeds the strength of the ice, the channels break open, allowing the basin to drain.

This year is different. In late June, an ice shelf more than 1,000 feet long calved into the basin. It was thought at the time that the titanic tumult might jar the channels open. Instead, the ice appears to have sealed the basin more tightly. With the subglacial channels blocked, the basin has filled to the point that it now tops the dam holding water within the basin.

Late Monday, the basin’s water began flowing over the dam and downhill, along the boundary between the glacier and the eastern rock wall that defines its border.

A helicopter video shared by Capital City Fire/Rescue on Monday (embedded below) shows that flow disappearing into the glacier after traveling several thousand feet downhill. In prior years, it has taken several days for water released from the basin to begin affecting the level of Mendenhall Lake and River. It is not clear whether this different avenue will also take several days to show effects.

In addition, it is not clear how quickly water will be released from the basin via this new channel. The flow of water over the dam is expected to gradually erode it, allowing more water to flow out of the basin.

“It’s too early to tell how this is going to evolve,” Jacobs said.

• Contact reporter James Brooks at or 523-2258.

More in Home

Juneau-Douglas High School: Kalé junior Kai Ciambor puts a shot past Ketchikan's Kingston Dell (11), Alex Gilley (1) and Eunchong Lee during the Crimson Bears 4-2 win over the Kings at Adair-Kennedy Field on Friday. (Klas Stolpe / For the Juneau Empire)
Crimson Bears eat Kings for pre-senior night pitch feast

JDHS boys soccer team one step closer to taking region title from Ketchikan.

Members of the Thunder Mountain High School culinary arts team prepare their three-course meal during the National ProStart Invitational in Baltimore on April 26-28. (Photo by Rebecca Giedosh-Ruge)
TMHS culinary arts team serves a meal of kings at national competition

Five students who won state competition bring Alaskan crab and salmon to “Top Chef”-style event.

Sen. Lyman Hoffman, D-Bethel, listens to discussion on the Senate floor on Wednesday. (James Brooks/Alaska Beacon)
A look at some of the bills that failed to pass the Alaska Legislature this year

Parts of a long-term plan to bring state revenue and expenses into line again failed to advance.

Rep. Genevieve Mina, D-Anchorage, stares at a pile stack of budget amendments on Tuesday. (James Brooks/Alaska Beacon)
Alaska lawmakers expand food stamp program with goal of preventing hunger, application backlogs

More Alaskans will be able to access food stamps following lawmakers’ vote… Continue reading

Nathan Jackson (left) and John Hagen accept awards at the Central Council of the Tlingit and Haida Indian Tribes of Alaska President’s Awards banquet. (Courtesy photo)
Haines artists get belated recognition for iconic Tlingit and Haida logo

Nathan Jackson and John Hagen created the design that has been on tribal materials since the ‘70s.

House Minority Leader Calvin Schrage (center), an Anchorage independent, talks with Reps. CJ McCormick, a Bethel Democrat, Neal Foster, a Nome Democrat, and Bryce Edgmon, a Dillingham independent, as a clock shows the midnight Thursday deadline for the 33rd Alaska Legislature to adjourn passed more than an hour earlier. (Mark Sabbatini / Juneau Empire)
33rd Alaska Legislature adjourns well past deadline, due to last-minute rush and disputes by House

Bills on correspondence schools, energy, crime pass on final day; election, other bills cause holdup

Dori Thompson pours hooligan into a heating tank on May 2. (Lex Treinen/Chilkat Valley News)
Hooligan oil cooked at culture camp ‘it’s pure magic’

Two-day process of extracting oil from fish remains the same as thousands of years ago.

Shorebirds forage on July 17, 2019, along the edge of Cook Inlet by the Tony Knowles Coastal Trail in Anchorage. The Alaska Legislature has passed a bill that will enable carbon storage in reservoirs deep below Cook Inlet. The carbon-storage bill include numerous other provisions aimed at improving energy supplies and deliverability in Cook Inlet and elsewhere. (Yereth Rosen/Alaska Beacon)
Alaska Legislature passes carbon-storage bill with additional energy provisions

The Alaska Legislature has passed a bill that combines carbon storage, new… Continue reading

Most Read