Moderate flooding is expected from a glacial dam outburst in Alaska's capital city

JUNEAU, Alaska — A flood warning was issued Saturday after an outburst from a glacial lake in Alaska's capital.

Suicide Basin is a side basin of the Mendenhall Glacier above the city of Juneau. Since 2011 it has released glacier lake outburst floods each year that cause inundation along Mendenhall Lake and the Mendenhall River.

“We expect moderate flooding from this event, not major flooding,” said Nicole Ferrin, warning coordination meteorologist with the National Weather Service in Juneau.

Residents had 24 to 36 hours to prepare for flooding, she said. The flood warning was in effect until Monday.

The forecast called for the river to crest at around 11 to 11.5 feet (3.35 to 3.5 meters) early that day, the weather service said.

Officials warned people to stay away from the river. Recent snow has made the banks very slippery.

Suicide Basin fills with rainwater and snowmelt during the spring and summer and at a certain point builds enough pressure to force its way out through channels it carves beneath Mendenhall Glacier.

The basin started refilling with fall rain over the last couple of months, Ferrin said. It was not certain how quickly it will drain or if it will empty completely.

In August, roughly 290 residences were damaged after the lake sent floodwaters into neighborhoods.

The Mendenhall River crested at 15.99 feet (4.9 meters) then, a new record, topping the level during last year’s flood by about a foot, and the water reached farther into the Mendenhall Valley, officials said.

Juneau, a city of about 30,000 people in southeast Alaska, is reachable only by plane or boat.