Permafrost, Phillips, Springman & Arenson (eds) © 2003 Swets & Zeitlinger, Lisse, ISBN 90 5809 582 7 Morphogenesis of frost boils in the Galbraith Lake area, Arctic Alaska C.L. Ping & G.J. Michaelson Palmer Research Center, University of Alaska Fairbanks, Palmer, USA P.P. Overduin Water and Environmental Research Center, University of Alaska Fairbanks, USA C.A. Stiles Department of Soil Science, University of Wisconsin, Madison, USA ABSTRACT: Frost boils (non-sorted circles) from different physiographic settings on the northern foothills of Alaska’s Brooks Range show contrasting physico-chemical properties as compared to those formed on uplands of the Arctic Foothills and Coastal Plains of Arctic Alaska. Frost boils in the Galbraith Lake Basin formed in relatively uniform fine-textured lacustrine sediments and occur in lineations along frost cracks sub-parallel and perpendicu- lar to the lake shoreline in somewhat poorly- to poorly-drained areas. These features have no vegetative cover, and finer textures (clays) than the surrounding tundra-covered sandy soils. At depth within the lacustrine frost boils, clayey material has been extruded into the surrounding sandy matrix suggesting that the saturated fine-textured sediments have been emplaced in a liquid form into the frozen sandy layer, creating a textural differentiation between soils under the tundra and those within the frost boil. Frost boils and surrounding soils in other areas of arctic Alaska do not have this differentiation and appear to have similar textures, indicating that extrusion emplace- ment is not a significant formation process in these dominantly silt-textured, upland tundra soils. 1 INTRODUCTION and surrounding tundra in the Galbraith Lake area have contrasting properties; the frost boils consist of fine- Cryoturbation is described as the process of deforma- textured lacustrine sediments that reflect the physical tion and mixing of soil caused by frost heave during and chemical nature of the parent rocks around the freeze back of the active layer (Van Vleit-Lanoë 1991). lake basin whereas the tundra soils are eolian sand. This process results in cryogenic features that include Most frost boils form along thermal contraction cracks warped horizons, frost-churned organic matter in the parallel to the lakeshore. lower active horizons and the upper permafrost, as well as sorted and non-sorted circles. However, some highly contorted layers and diapiric forms suggest that 2 PHYSICAL ENVIRONMENT some cryoturbation occurs by viscous flow of thawed soil (Swanson et al. 1999). Frost boils are one kind of The study site is located in the Galbraith Lake Basin non-sorted circle and some researchers have suggested in the foothills of the northern flank of the Brooks that some periglacial ground patterning, especially Range. The area lies within the continuous lowland frost boils, could result from this same density-driven permafrost regions described by Ferrians et al. (1969) differential viscous flow (Hallet et al. 1988). where permafrost can reach a depth of 200 m under Frost boils occur on exposed areas in tundra zones. the coastal margin of the Beaufort Sea. The Brooks They are found in regions of arctic coastal plain tundra Range foothill/piedmont areas have been through sev- to subarctic tundra. Generally, frost boils form on eral episodes of Quaternary glaciation (Hamilton 1987) exposed landscape positions, influenced by strong and have deep flat-bottomed, U-shaped valleys invari- winds that keep these areas relatively free of snow. ably containing shallow, broad-braided streams drain- However, frost boils are also found on poorly drained ing northward out of the Philip Smith Mountains lowlands in the Arctic Coastal Plains and basins of the in this area. Galbraith Lake Basin lies within one of Arctic Foothills of Alaska. On the uplands of the Arctic these glacial valleys and is situated in Pleistocene Foothills, the frost boils occur in clusters of more or glacio-fluvial deposits within Late Mississippian/Early less circular vegetation-free patches and in soils con- Permian age uplands (Brosge et al. 1979). This area sisting mainly of silt-sized particles (Bockheim et al. has notable cryohydrogenic features such as aufeis 1998; Ping et al. 1998; Walker et al. 1998). These accretions, pingos and continuous lineations of frost upland frost boils are moderately well to somewhat boils as part of the landscape. Galbraith Lake itself is poorly-drained and form in parent materials similar the remnant of a large lake dammed by a glacier that to the surrounding soils. However, soils of frost boils drained periodically throughout the Early Quaternary 897 of each horizon to permafrost in the center of the frost boil; and (2) 15 cm distance from either side at 25 cm depth. Soil samples were also taken outside of the frost boil areas as a control. The samples were stored in a cooler and shipped to the laboratory, where they were air-dried and crushed to pass 60-mesh (2 mm) sieve before characterization analyses. 4 RESULTS AND DISCUSSION The cross section of soils formed under a frost boil and the surrounding tundra at the Galbraith Lake site is shown in Fig. 2. Figure 1. Location of the study site in Arctic Alaska. The grayish Cf horizons belong to the clay bed and the gleyed Bg horizons are the portions of clay that intruded into the adjacent sandy soils. Soils in the tun- up to the end of the Wisconsin glacial interval. Glacio- dra areas surrounding the frost boils have 5 to 12 cm lacustrine parent material sediments are locally derived organic horizon (Oi) overlying a loamy sand layer from the Mississippian age Lisburne Group (dolomitic consisting of a dark gray 2A and a bluish gray 2Bg limestones and argillaceous shales), Permian age horizons that overlies a clay layer. In contrast, the frost Echooka Formation (calcareous siltstones and bioclas- boils have a clayey texture throughout. The frost boils tic limestones), and the Late Cretaceous age Fortress are moderately well-drained at the surface, where the Mountain Formation (iron-enriched conglomerates, grayish brown colors (AC and Bw) indicate increased shales and interbedded sandstones) that comprise oxidation. The gleyed colors at the frost boil margins extensive exposed sequences near the lakebed (Brosge indicate limited drainage toward their edges due to a et al. 1979). raised frost table (Cf3). Selected properties of the The study site is located north of Galbraith Lake soils formed under the frost boil and the tundra are next to a small shallow remnant lake (Fig. 1). Frost presented in Table 1. polygons with diameter of more than 10 meters form Most soils of frost boils in this area have a columnar around the shoreline in a concentric pattern. Frost boil structure in the surface horizon, a result of the both lineation form along the polygon cracks, with a range the shrinking of clay-rich parent material and saline of diameters from 80 to 160 cm. Recently formed soil solutions. The mineral soil horizons have an alka- frost boils are as small as 20 cm in diameter. The site line reaction throughout the depths (pH 7.8–8.1) and a is somewhat poorly-drained and the water table is narrow range of carbon content (2.2–4.0%) suggest- within 20 cm during the growing season. The area has ing the uniformity of the soil from different horizons. a landcover type of moist non-acidic tundra according The high clay content (Ͼ46%) and low CEC of the to Auerbach et al. (1996). The vegetation consists of mineral horizons indicate the presence of low-activity Dryas integrafolia, Salix lenata, Carex spp., and moss clays. Tomyhypnum spp.). This is verified by mineralogical studies of the clay fraction that indicate the predominant clay minerals are kaolinite, chlorite, Al-interlayered hydromicas 3 METHODS and pyrophyllite (Stiles & Ping 1996). The dominant cations on the exchange complex are Ca and Mg, with A soil pit was excavated across a frost boil complex to a base saturation of 80–87%, characteristic of non- a depth of Ͼ100 cm that extended below the active acidic tundra in the area (Ping et al. 1998). Vertical layer and into the upper permafrost. A total of three cracks of the columnar structures reach to a Ͼ20 cm pits were excavated. Soil morphology of each pit depth. The dominantly clay texture, the chemical pro- was studied and described according to Soil Survey perties and the clay mineralogy all indicate that this Manual (Soil Survey Division Staff 1993). Cryogenic material is of lacustrine origin. The bedrock lithology fabrics were described according to French (1988). is also reflected in both the chemical properties as Soil horizon nomenclature follows Soil Survey Staff well as the clay mineralogy. The sandy layer (2Bg) (1999). Each pit was photographed and the soil hori- above the clayey layer has a similar soil reaction to the zons (or soil zones) identified on a drawing with clayey layer (pH 7.9) due to the parent rocks in the boundaries marked on a grid. Soil samples were taken Atigun Valley and the lowland position. The sandy from the frost boil in two transects: (1) from the center layer is reworked material from sand dunes (Kreig & 898 Galbraith Lake basin are: 1. During freeze up, the sandy layers overlying clayey layers begin to freeze first, while the clay layer below remain saturated. 2. These clayey layers remain unfrozen due to the high salt content, and the water content within the profile reaches the liquid limit. 3. Cryostatic pressure exerted by the overlying frozen sands and freeze-up from the permafrost forces the Figure 2. The cross section of soils formed under a frost still liquid clayey materials to be extruded from boil and the tundra at the Galbraith Lake site, Arctic the weakest location within the profile: along the Alaska.