Solifluction

If you sit still in the subarctic for long enough, you risk being run over by just about anything. Glaciers, volcanic ash falls, land slides, rock glaciers, land slumps, mud flows--you name it--if there is a source of detritus, a lubricant to smooth the way, and gravity to propel it, it'll move.

One of the more curious forms of earth movement which are common on the alpine hillsides of interior Alaska are solifluction flows. Solifluction lobes can be seen drooping downhill near many of the roads in the Interior, including the Steese and Taylor highways. A hillside covered with these reminds one of oozing, sagging makeup on an aging actor under the hot lights in a horror movie.

Solifluction is a combined flow and slip movement, involving the surface layers in areas of permafrost. The surface layers thaw to only a small depth during the short summer, and find themselves situated on very slippery footing. Meltwater and rain saturate the soil in the springtime because they cannot percolate into the frozen layers below. This creates a very unstable situation at the interface between the frozen and unfrozen layers, and the heavy, waterlogged bed on top flows downslope as a dense sludge lubricated by the semi-liquid layer below. Solifluction can occur on even moderate slopes, because of the ease with which a lobe slides on the frozen substratum.

By landslide standards, this does not occur abruptly, but solifluction lobes can move downhill as rapidly as several inches per day--almost enough to disturb a picnic.