Far above the rugged, glacially carved valleys filling the nooks and crannies of Southeast Alaska's coastal range lurks a hidden hazard.
It emanates from ice- or debris-dammed lakes that form at the edge of a glacier.
During mid- to late-summer months, the pressure on the glacier, or its moraine, builds as the lake level rises.
In the few places where the icy menace of a jökulhlaup (YO-kul-hloip) is well-known - such as Juneau's Taku River - riverfront cabin owners brace themselves, securing their boats from a sudden deluge.
In Yakutat, some residents are lobbying for a multimillion-dollar diversion ditch that would divert floodwater unleashed by Hubbard Glacier from Russell Fjord away from the Situk, a world-class fishing river.
In perhaps dozens or even a couple hundred remote spots in Southeast Alaska, a jökulhlaup may erupt once or twice each summer, breaking a lake's glacial dam and releasing frigid water.
The jökulhlaup emanating from a lake alongside the Tulsequah Glacier in Canada often carries live trees like missiles into the Taku River.
In a bad year, docks at fish camps and massive sections of river bank fronting Taku River cabins may crumble into the torrent.
Sometimes Canadian Taku River fish wheels have been carried off by a bad jökulhlaup. And rafters have been stranded when their boats were carried away, Juneau hydrologist Ed Neal said.
That's not anything like the danger that Skagway, Yakutat and Hyder have faced in both recent and past memory.
Gary Benedict, who owns the Sealaska Inn in Hyder, remembers the town's first jökulhlaup in 1961 with dread.
Not only did it drown some cats, but, "It just about washed the whole town away. No one even knew where the water came from," he said.
Jökulhlaups were "washing all the salmon spawn out of Fish Creek. It did that for two years (in the 60s)," until the town acquired funding to build a new dike to protect the salmon spawning beds, said Hyder resident John Catron.
Hyder lost a steel bridge spanning Texas Creek and a large dike to jökulhlaups, which have grown less severe there in recent years.
Jökulhlaups, like the glaciers themselves, are a remnant of the little Ice Age that have been retreating from their past dominance over the coastal mountains.
"They are kind of hard to predict," said Neal, with the U.S. Geological Survey.
Hyder's jökulhlaups come from the draining of Summit Lake, which is dammed by the Salmon Glacier and is the largest self-draining, ice-dammed lake in Canada, according to a 1992 Canadian scientific study.
In 2002, Skagway and Dyea, a town across Taiya Inlet, got a nasty surprise when they tasted their own very big and bad jökulhlaup.
The National Park Service had to rescue some residents and tourists flooded out by the release of water-logged sediment and floodwaters from a glacial dam above a tributary of the Taiya River, said doctoral geology student Denny Capps, who did a hazard assessment of the jökulhlaup.
"No one washed away but there was a critical hour of rescue out of the campground," Capps said.
There are more jökulhlaups in Southeast and Southcentral Alaska than anywhere else in the world, Capps said Friday.
A native of Louisiana well versed in the danger of floods, Capps became captivated with glaciers and is now studying the jökulhlaups of the St. Elias Mountains for his dissertation at Simon Fraser University in British Columbia.
The hard-to-pronounce term was coined by Icelanders and according to one translation, literally means "glacier jump," Capps said.
Unlike the jökulhlaups in North America, Icelandic glacial outburst floods occurred when volcanoes under the surface of a glacier melted large quantities of ice and generated floods, he said.
Based at Glacier Bay National Park & Preserve this August, Capps is studying glacially dammed Abyss Lake, which had at least two jökulhlaups that sent trees and other debris into Dundas Bay this summer.
Capps believes that some of the glacial lakes that form in Southeast Alaska's coastal mountains could be ticking time bombs.
A 1971 study identified about 700 glacially dammed lakes in Alaska, he said.
One way to determine the level of risk posed by jökulhlaup is to measure the volume of the glacial lake. When the lake empties out, that's the volume that will be released downstream.
Some are in such remote areas that they go unnoticed for years, said Neal, the Juneau hydrologist.
Neal, who works for the U.S. Geological Survey, recently returned from a field trip to the Alsek River and noticed an anomalous jump in water levels at a river gauge.
After making a series of phone calls, Neal said he figured out that a jökulhlaup had occurred in the river.
Looking over maps of the coastal range with a U.S. Geological Survey geologist who also spent time at Glacier Bay this summer, Capps said that the proposed Juneau access road to Skagway lies in the path of some glacially dammed lakes in the Berners Bay and Katzehin river drainages.
One lake is almost four miles long, he said.
The potential of jökulhlaups was studied in 1994 during the proposed road's reconnaissance engineering study, according to state Department of Transportation project manager Reuben Yost.
"We look for evidence of scouring," Yost said. Any jökulhlaups that have occurred in these drainages haven't been big enough to leave scour marks above the rivers' high water mark, he said.
Capps decided to study the jökulhlaups in the St. Elias Mountains but may extend his study to other areas in Alaska.
He hopes to create a computer program that will draw on satellite images and complex algorithms to identify areas where jökulhlaups are likely to occur.
"We recognized that they haven't been looked at throughout time," Capps said.
Elizabeth Bluemink can be reached at firstname.lastname@example.org.
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