Kluane Lake is one of the Yukon's crown jewels. The largest lake in the territory, its azure blue waters extend for 70 kilometres, draining north until they eventually mix with those of the Yukon River.

But fast forward a century or so, and Kluane Lake might be slightly less grand. Most of its water flows out of the Kaskawulsh Glacier, and -- like all of the major glaciers in the St. Elias Mountains -- this massive sheet of ice is retreating.

Now about 80 percent of the meltwater draining out of the glacier flows north into Kluane Lake via the Slims River. The rest of the melting ice feeds the Kaskawulsh River, which flows east and south into the Alsek River and on to the Pacific Ocean.

Every decade or so, this pattern is reversed and most of the glacier's meltwater flows into the Kaskawulsh River. Water levels in Kluane Lake drop when this happens. If a change of direction became permanent, the lake water might also warm up as it would not be fed by icy glacial water through the summer.

That scenario is just one of the many possible ones for the St. Elias area, according to Peter Johnson, a geographer at the University of Ottawa. He has been studying the glaciers flowing out of the St. Elias Mountains for three decades, speculating on what will happen as these massive sheets of ice slowly melt away.

Johnson thinks that conditions underneath the ice cause the changes in direction. Water flowing underneath the glacier is under a great deal of pressure, and can cause channels to collapse and change course quickly.

While working by the terminus of the Donjek Glacier, he witnessed how quickly new channels can form. During one ten-day interval, he watched the water flowing out of the glacier change course twice, switching from one side of the valley to the other.

Up until a few years ago, the Donjek River ran along the east side of the valley. Then it was diverted underneath the ice, causing a channel to collapse and a small lake to form. In 1998, when the dam at the head of the lake gave way, a large wave of water swept down the Donjek River.

"It distributed blocks of ice for ten kilometres down the valley," says Johnson. "There were ice blocks all over the valley floor."

About ten years ago Johnson began noticing some of the effects of the retreating glaciers, such as lakes that form on some glaciers in the summer.

For example, a small lake used to form at the confluence of the north and central arms of the Kaskawulsh Glacier. As the glacier continues to retreat, Johnson suspects that it may not form in the future, but melting ice could form new lakes in other places.

Even though the major glaciers are all edging backing into the mountains, some glaciers will periodically surge. A number of glaciers in the St. Elias Mountains are known for their spectacular leaps forward.

The Lowell Glacier has surged forward several times in the past, completely blocking the Alsek River and forming a huge body of water called Glacial Lake Alsek. When an ice dam on the lake gave way about 150 years ago, a wall of water roared down the Alsek River as the lake drained.

Glaciers surge at regular intervals, and the Lowell leaps forward about once every 15 to 20 years. But Johnson does not think that Glacial Lake Alsek could form again, as the glacial ice is thinner now and less capable of forming a dam across the river.

It is now known how fast glaciers might be retreating, as there are no regular glacier-monitoring systems in the St. Elias Mountains. Johnson thinks that the rate of retreat has increased in the last decade or so, and expects that trend to continue. He says that if people want clues as to what Kluane might look like in another century or so, they should take a drive over White Pass on the Skagway Road.

"There was 1,000 metres of ice sitting there 10,000 years ago. Melt all of the ice in the St. Elias and the country will look more like White Pass," he says.

Peter Johnson can be contacted at peterj@aix1.uottawa.ca. An abstract of his work, "Change and Variability in the Hydrology of the Boundary Ranges of the St. Elias Mountains" can be found at http://www.taiga.net/arctic2000/abstracts/johnson.html.