Origin and Significance of Wet Spots on Scraped Surfaces in the High Arctic
AbstractIn the western Queen Elizabeth Islands, Northwest Territories, where most of the petroleum exploration in the High Arctic is being conducted, much of the low lying land is covered with sorted and non-sorted circles and polygons 0.5-2.0 m in diameter. ... Much of the oil-camp construction takes place on the coastal low-lands on polygonal surfaces composed of sandy to silty loams. When these surfaces are scraped and reworked for camp areas and air strips in summer, it is common for them to have numerous wet spots which become soft and spongy and of jelly-like consistency when equipment is moved across them .... a small study was conducted in 1972 at the Sunoco Camp no. 3002 on the northeast side of King Christian Island (77° 44'N, 101° 15'W), approximately 3.5 km from the sea. There the surface soils consist of fine marine sediments intermixed with small pebbles. The entire camp area and the Hercules landing strip are built on a surface covered with non-sorted polygons. ... Excavations were made on both the disturbed surface, where the damp spots occurred, as well as in the undisturbed area adjacent to the camp. ... From the information obtained during the excavations in each of the areas described, it is possible to understand more clearly the mechanisms responsible for the features. The wet spots in the cleared work-area are located at the foci of ground-ice accumulations which occur at the margins and intersections of the non-sorted patterned ground. The occurrence of ground-ice at the perimeters of the non-sorted polygons is explained by the contraction cracks which form and outline the patterned ground. Moisture from the scanty precipitation (especially blowing snow) accumulates in the cracks and eventually becomes incorporated in the underlying frozen ground as ice veins. Since the cracks are areas of greater moisture (as well as microhabitats), the plants tend to congregate in them and in turn reinforce the moisture content by (1) their greater moisture-holding capacity, (2) more efficient moisture entrapment, and (3) retarding the rate of thaw owing to the slightly greater insulation they provide. Once such a surface is disturbed, as it was in this case by light blading with a bulldozer, the vegetation is destroyed (at least the above- surface parts). Greater thawing may then occur, during which the moisture is drawn to the surface by capillary action as melting of the ground ice takes place. These bladed areas increase soil compaction and therefore thermal conductivity, and so melt is accelerated. In addition, the organic matter and remaining live plant material in the crack act as a "wick" drawing the moisture to the surface. A last but very important factor is the movement of heavy equipment over the surface. ... Their main area of concentration was in the work area in front of the camp where there was continual movement of equipment. The repetitive application of pressure over an area rich in ground ice ... has a "pumping" action whereby moisture is slowly forced to the surface. This constant agitation distributes the water throughout the mass, and the material becomes "quick" owing to the reduction of intergranular pore pressure. This results in loss of cohesion, and the material becomes spongy and jelly-like when pressure is applied. The practical significance of this brief investigation is that the wet spots will probably not increase in size or the surface deteriorate further, but in fact there should be an improvement. It appeared from discussion with camp managers on two islands that, after two or three summers of use of the surface and scraping, the wet spots dry out. The best approach to the use of these vegetated (and therefore ice-rich) non-sorted, patterned ground surfaces in the High Arctic is to clear the areas before thawing occurs in the spring, and if possible not to use them heavily during the first one or two summers. By the second or third summer much of the ground ice will have thawed, so there should be less chance of major problems with wet and soft spots - unless the summer is unusually wet, as it was 1973.