Origin and Significance of Wet Spots on Scraped Surfaces in the High
Total Page：16
File Type：pdf, Size：1020Kb
Origin and Significance of northeastside of KingChristian Island (77"44'N., 101"15'W.), approximately 3.5 Wet Spots on Scraped Surfaces km. fromthe sea. Therethe surface soils consistof fine marine sediments intermixed in the High Arctic* with small pebbles.The entire camp area and theHercules landing strip are built on a In the westernQueen Elizabeth Islands, surfacecovered with non-sorted polygons. NorthwestTerritories, where most of the On17 July the active layer was 30-50 cm. petroleum exploration in the High Arctic is deep in undisturbed land 200 m. from camp. being conducted, much of the low lying land In thesePolar Semi-desert landscapes is covered with sorted and non-sorted circles 20-40% of the surface is often bare because and polygons 0.5 - 2.0 m. indiameter2 of the activepolygons. Flowering plants The central parts of these islands are usually constituteabout 15% cover,lichens 15%, considered as true Polar Desert with shallow mosses 25%, and dead plants (litter) 5% at lithosols andlittle or no vegetation.2.3 The this site. The dominant flowering plants are coastal areas are referred to as Polar Semi- Papaverradicatum, Alopecurus alpinus, desert, since the marine sediments support a Luzula nivalis, and Drabaalpina. Mosses fairly complete cover of lichens, mosses and appear to initiate plant succession and to act a few scattered flowering plants, usually con- as a spongein holding water for flowering centrated at the marginsof the non-sorted pat- plantsin an environment that is typically terned ground features3 Muchof the oil-camp quite dry after snowmelt. construction takes place on the coastal low- Excavationswere made on boththe dis- landson polygonalsurfaces composed of turbed surface, where the damp spots occur- sandy to silty loams. When these surfaces are red, as well as in the undisturbed area adjacent scraped and reworked for camp areas and air to thecamp. One relatively large wet circular strips in summer, it is common for them to area 1.O - 1.5 m. in diameter was excavated in have numerous wet spots which become soft thework area (Fig. 2). Theupper 10 cm. and spongy and ofjelly-like consistency when were slightly drier and more dense and cohe- FIG. 1. Wetspots occurring on scraped surface in work area of Sunoco Campno. 3002 on N. E. King Christian Island. This area was initially cleared during the spring of 1971. Photograph taken on 17 July 1972. equipment is movedacross them (Fig. 1). sive than the underlying material, which was Althoughsurfaces are often scraped daily, wet and sticky. The centre of thewet spot the abundance of these soft spots may force was found to beunderlain by an ice-rich the abandonment of air strips, or even yard domed area approximately 50 cm.in diam- areas, for much of the summer. eter.The depth to the apex of theice-rich Since the authors have observed numerous basewas 47 cm., while thesurrounding placesin the islands where it is difficult to frozen ground was 52 cm. below the surface maintainair strips in summer due to these (Fig. 2). When the base of the excavation was wetspots, a small study was conducted in scraped with a shovel, many small ice veins 1972 at the Sunoco Camp no. 3002 on the 1 - 5 mm. wide and 20 - 50 cm. long could be seenradiating across the convex area, but *DevonIsland International Biological Pro- essentially none occurred in the surrounding gram ecosystem study, paper no. 26. frozen base. The authors could not ascertain SHORT PAPERSAND NOTES 305 FIG. 2. Excavated wet spot from disturbed site at Sunoco Camp. The vertical wooden stakesare 56 cm. long and reflect the doming of the ice-rich area of the underlying ground. the depth of penetration of the ice veins, but excavationsin each of theareas described, from their size and from other observations it is possible to understand more clearly the inthe region assumed thatthey did not mechanisms responsible for the features. The penetrate more than 0.5 - 1.0 m. below the wet spots in the cleared work-area are located active layer. Such depths of this ice-rich zone at the foci of ground-ice accumulations which havebeen observed in cutsmade on other occur at the margins and intersections of the islandswith similar soils.4 The ice-rich and non-sorted patterned ground. The occurrence slightly domed area was centred immediately of ground-ice at the perimeters of the non- below the wetspot on the surface, so the sorted polygons is explained by the contrac- source of the moisture was clearly identified. tioncracks which form and outline the Moreover,the evidenceseemed tosupport patterned ground. Moisture from the scanty theinitial observation .thatthe .wetspots precipitation(espccially blowing snow) ac- coincidedwith centres of the non-sorted cumulates in thecracks and eventually be- polygons, although this was later found not comes incorporated in the underlying frozen to be the case. ground as ice veins. Since the cracks are areas Two excavationswere then madein the of greater moisture (as well as microhabitats), undisturbed area adjacent to the camp. These the plants tend to congregate in them and in were done in such a way as to transect the turnreinforce the moisture content by (1) centre and margins of the patterned ground theirgreater moisture-holding capacity, (2) features.The camp area itself wasnearly more efficient moistureentrapment, and (3) level, butthe surface was inclined 1 - 3 to retarding the rate of thaw owing to the slight- the northwest, and the polygons were slightly ly greater insulation they provide. elongated in the direction of the slope. Ice- Once such a surface is disturbed, as it was rich slightly domedareas were also discovered in this case by light blading with a bulldozer, herebut, it is importantto observe,they the vegetation is destroyed (at leastthe above- coincided with the margins and intersections surfaceparts). Greater thawing maythen of the polygons, not the centres. The active occur, during which the moisture is drawn to layer was on average 12 cm. shallower in the the surface by capillary action as melting of non-disturbed areaas opposed tothe dis- the ground ice takes place. These bladed areas turbed site, and there was less difference be- increasesoilcompaction andtherefore tween the levels of the ice-rich and ice-poor thermal conductivity, and so melt is ac- areas. The depth of the activelayer above celerated.4 In addition, theorganic matter the ice-rich base was 36 cm., while it was 39 and remaininglive plant material in the crack cm. to the surrounding frozen ground. There act as a "wick" drawing the moisture to the were no wet spots in the undisturbedsite, and surface. the material was friable andeasy to excavate. A last but very importantfactor is the There was also no unfrozen water at the base movement of heavyequipment over the of the excavation at the zone of contact with surface. It was found during the field recon- the ground ice. It began to melt quickly as naissance of 1972 that the wet spots did not soon as it was exposed, however. occur in the sleeping-quarter area or on the From the information obtained during the runway, although in the previousyear, and 306 SHORTPAPERS AND NOTES also in 1973, the air strip contained numerous R. R. Riewe, D. W.A. Whitfield and P. wet areas. Their main area of concentration Widden. 1973. Arctic tundra ecosystems. was in the work area in front of the camp Annual Review of Ecologyand System- where there was continualmovement of atics, 4: 359-99. equipment. The repetitive application of pres- 4Babb, T. A. and L. C. Bliss. 1974. Effects sure over an area rich in ground ice (such as of physical disturbance on arctic vegetation by a fork-lift when unloading aircraft) has a in the Queen Elizabeth Islands. Journal of “pumping” action whereby moisture is slowly Applied Ecology, 11: 549-62. forced to the surface. This constant agitation speck, R. B., W. E. Hanson and T. H. Thorn- distributes the water throughoutthe mass, burn. 1953. Foundation Engineering. New and the material becomes “quick” owing to York: John Wiley. the reduction of intergranular pore pressure.5 This results in loss of cohesion, and the material becomes spongy and jelly-like when The Use of APT Satellite pressure is applied. The practical significance of this brief Imagery in a Subarctic investigation is that the wet spots will prob- Airborne Oceanographic Survey ably not increase in size orthe surface deteriorate further, but in fact there should GENERAL be an improvement. It app-ared from discus- sion with camp managers on two islands that, Duringan airborne oceanographic survey after two or threesummers of use of the of ice conditions in the east Greenland drift- surface and scraping, the wet spots dry out. stream in April 1972, earth-oriented satellite The best approach to the use of these veg- photographs were received aboard theresearch etated (and therefore ice-rich) non-sorted, aircraft Arctic Fox of the U.S. Naval Ocean- patterned ground surfaces in the High Arctic ographic Office. Thesephotographs, broad- is to clear the areas before thawing occurs in cast directly from the satellites Nimbus 4 and the spring, and if possible not to use them ESSA 8 (Environmental Survey Satellite) heavily during the first one or two summers. were received by means of an APT(automatic picture transmission) satellite receiver station1 By the second OT third summer much of the ground ice will have thawed, so there should equippedwith a specially-modified airborne be less chance of major problems with wet satellite communication antenna. and softspots-unless the summer is un- The satellitephotographs showed the ice usually wet, as itwas in.1973. and cloud conditions for the Greenland Sea as they existed -during each flight.