Ice blocking the Knik River near Palmer/Greg Johnson photo

A lobe of the Knik Glacier has cut off the flow of the river of the same name near Palmer, Alaska, leaving some recent visitors to the remote headwaters wondering if a glacially dammed lake that hasn’t existed for decades could be forming once again.

From 1918 until 1966, the glacier regularly blocked the river and the water behind it backed up to create an impoundment more than 100-feet deep named “Lake George.” Five decades have passed since that last happened, but the New York Times was worried about the possibility of a new ice dam as late as 1985.

“The fear that a dam will again be created by the Knik Glacier once again hangs like an icy Sword of Damocles over the Knik River valley,” the Times’ Walter Sullivan reported in October of that year.

“Every year from 1918 to 1966, with one exception, the Knik Glacier blocked drainage from a tributary valley and spring melt-water raised the water level 160 feet….Then, each summer, water poured over the edge of the ice dam and began to cut an escape route through the glacier, where it abuts Mount Palmer,” Sullivan wrote. “The flow gained momentum, sweeping jumbled blocks of ice from its path and cutting a gorge 300 feet deep and five miles long.

“In the valley beyond, the lazy trickle of the Knik River, long starved of its water supply, became a destructive flood. It swept away bridge approaches, buried highways and inundated farms.

“In earlier outbreaks, before settlement of the valley was curbed, Indian villages were entirely destroyed. In the 1920’s a community planned at Matanuska, where the Alaska Railroad and Glenn Highway cross the valley, was abandoned because of flood damage.”

Those who remember the worry of the 1980s wonder what would happen if the bad, old days were to return.

Long time Alaskan Greg Johnson noted the growth in the Knik valley downstream from the glacier. There are now homes and subdivisions along the river, and Johnson said that when the state redesigned the Glenn Highway 30 years ago it was not designed to deal with the major outburst floods that then appeared to be ancient history.

DON’T PANIC

Johnson and others worry about the possibility of future disasters, but hydrologists with the U.S. Geological Survey in Anchorage don’t think there’s any need to worry at this time.

The current block, they said, looks to be a replay of a temporary, seasonal phenomenon that has taken place over the course of several past winters. It has likely gone unnoticed by most people because of a couple of snow-short winters when snowmachine riders found it difficult to ride to the glacier, said USGS hydrologist Jeff Conaway.

Good snow this year has allowed a lot of people to explore the Knik valley once more.

Snowmachine riders exploring the ice-blocked Knik River/Greg Johnson photo

Many of the riders have gone far enough past the terminus of the glacier to notice the wall of ice blocking the opening between its southwest edge and the Mount Palmer bedrock to which Sullivan referred.

Conaway and others believe that ice is mainly just a jumble of icebergs that failed to wash out on the last high water of the fall.

“We don’t have the river flow there to move those icebergs out,” Conaway said. “It’s just a small tongue (of ice) out against the bedrock.”

The tongue Conaway describes is obvious in an aerial photograph taken by Shad O’Neel of the USGS earlier this month. The photo clearly shows snow-covered Inner Lake Gorge contained by a geographic feature named simply Low Ridge to the north. Low ridge at the top of the obvoius, frozen lake in this photo:

USGS photo

The Knik Glacier is in the center of the photo. To the left of the glacier is The Gorge where Lake George formed when the glacier dammed the river in the past. About halfway between the southern edge of the glacier and the broad, open expanse of the Knik River valley to the north is the tongue to which Conaway refers.

“Jeff is right that the thermo-mechanical erosion shuts off in winter, and the terminus pushes forward a bit,” O’Neel emailed. (There are) other factors, too, not uncommon for winter advances.  It does seem to float either continuously or when spring comes.  The closure has been reported in recent years, but no major outburst has been reported. The area that is pinched is very small when seen from the air.”

Both hydrologists are hopeful this remains the seasonal scenario for decades to come.

“I like to see destruction just as much as any young boy,” Conaway confessed, but it would be a real disaster if it happened in the Knik River valley of today.

And the odds are the Knik Glacier will stay put. Most Alaska glaciers have been thinning and retreating in recent years.  The retreat has been tied to global warming.

But even as most glaciers have retreated, there have been exceptions.

The Hubbard Glacier near Yakutat has advanced and retreated repeatedly in recent years, and there are now concerns it could advance to dam Russell Fjord by mid-century. A new lake forming in Russell Fiord coud threaten the Yakutat area with flooding.

And the Skilak Glacier on the Kenai Peninsula has regularly dammed the Skilak River in recent years. Fortunately, as was the case this year, releases from the dam above Skilak Lake have come in the late fall or early winter when flows on the Kenai River, into which Skilak drains, are low.

The latest release last October caused the Kenai River to rise by nine feet,  but it fell short of flood stage because it was running so low at the time. The Peninsula Clarion, the local newspaper for the Kenai, noted the water rising, but reported no serious damage.