Massive quantities of snow accumulate as moist Pacific air moves over the St. Elias Mountains, feeding the St. Elias Icefields. Valley glaciers radiate out from the icefields, fed by the icefields themselves. Glacial movements are often immense and spectacular and the St. Elias Mountains are home to the greatest concentration of surging glaciers in North America.
Surge type glaciers alternate between quiescent periods of slow movement and brief periods of fast surging motion when the toe of the glacier rapidly advances. During the quiescent period the glaciers continue to slowly flow, but ice gradually builds up in the accumulation area until a threshold is reached at which point ice is rapidly transferred down-glacier in a surge.
During a surge a glacier can move 100 times faster than usual leaving ice stranded on valley walls and forming jumbled ice cliffs, chaotic crevassing and seracs on its surface. The toe of the glacier advances down valley, often by several kilometres in a matter of months. The advance doesn’t mean there is more glacial ice, but that the ice is moving downhill more quickly. Milder temperatures at the glacier’s terminus cause the ice to melt more quickly and the toe of the glacier recedes. And the cycle begins again.
In the past, surges of Nàłùdäy (Lowell Glacier) have dammed the Alsek River at Goatherd Mountain. The resulting lakes extended well back to and over the present site of the Village of Haines Junction. The most recent Neoglacial Lake Alsek drained around 1850 in two days after the ice dam broke, with a flow rate comparable to that of the Amazon River. Huge gravel current ripples from this outflow, as well as wave-cut lake benches, are visible in the park along the Alsek Trail. The flooding events associated with Nàłùdäy's surges are the subject of Southern Tutchone First Nation people's legends and stories.
Since 1948 Nàłùdäy has surged five times, once about every fifteen years. This is the largest number of surges documented for any surging Yukon glacier. Even though the toe has rapidly and dramatically advanced each time, causing consternation, it hasn’t caused a complete blockage of the river. And a pattern is emerging. Each surge is a little less pronounced and doesn’t last quite as long as the previous one.
Over the same period Nàłùdäy has undergone significant wasting, which is consistent with other glaciers in the region, and likely underlies the reduction in surge extent and duration. Even if a surge were to completely block the river today, Nàłùdäy's ice has thinned so much that the impounded lake would likely spill over the top of the ice dam before the rising lake waters would reach Haines Junction. That's good news for the Village.
More recently, during the summer of 2018, record temperatures resulted in a massive “snow swamp”, a slushy mixture of snow and melt water, forming on the upper reaches of Nàłùdäy surface. While the phenomenon itself is not unusual in the warm summer months, its size (45 square kilometres) and the speed with which it formed (a matter of several days) were unprecedented. Over the next several weeks the melt water drained into Lowell Lake at Nàłùdäy's toe increasing the rate of flow in the Alsek River downstream of the lake. A little more ice shed from an already thinning glacier. And a reminder that the warming world we are inhabiting might not be good news for glaciers.