Slush Flows

The last thing anyone needs is to be caught up in a churning slurry of meltwater, snow and other debris sometimes-moving down slope fast enough to carry 75-ton rocks across even gentle slopes. Called slush flows, slush bursts, slushers, slush flow avalanches or water avalanches, these flows tend to occur during rapid spring breakup in arctic and subarctic alpine regions.

Slush flows are known to occur in the Brooks Range, in the mountain areas of Alaska's Seward Peninsula and occasionally in the Talkeetna Mountains near Anchorage. During the summer of 1980, a road grader on the Alaska pipeline haul road was struck by a slush flow. It caused no damage other than to pack icy slush around the grader's engine, but the driver was lucky that the flow was small.

Much more serious was a slush flow that struck the small coal mining settlement of Longyearbyen, Spitsbergen, on June 11, 1953. Not realizing the danger, people there built several houses and a hospital on a debris fan formed by earlier slush flows. The buildings stood for a decade until the fateful day "a turbulently tumbling wall of slush, rock debris, and ice blocks advanced rapidly down the valley toward the hospital complex. This moving tongue slammed into the upper group of buildings and they disintegrated as if swatted into oblivion by a gigantic hand." This graphic description of the event that killed three and injured twelve persons was given by Fairbanks geologist Richard D. Reger at a recent Alaska Science conference.

Slush flows occur during spring breakup in locations where an accumulation of snow becomes saturated with water. Dr. Reger and his coworkers have found that the most dangerous times are when the temperature has risen to about the 40°F (5°C) mark and remained there for 24 or more hours. Afternoon is the worst time for slush flows.

Dry snow avalanches typically release from slopes steeper than 25 degrees, but slush flows can cascade from slopes as gentle as 3 or 4 degrees--practically level ground. Sometimes slush flows churn along slowly, at other times they move faster than 25 mph (40 km/h). A small slush flow may be only a foot or so thick, but those thicker than 50 feet have been observed. Owing to the high density of a slush flow, due largely to its high water content, the flows have high momentum--like a moving locomotive, they are almost unstoppable and, therefore, are highly destructive.