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HomeMy WebLinkAboutResponse to Permafrost Terrain to Disturbance PP. 1-17 1986ENV 057 Alaska Power Authority LIBRARY COPY RESPONSE OF PERMAFROST TERRAIN TO DISTURBANCE: A SYNTHESIS OF OBSERVATIONS FROM NORTHERN ALASKA, U. S. A. DANIEL E. LAWSON Reprinted from Arctic and Alpine Research, Vol. 18, No. 1, 1986, pp. 1-17 ENV os7 Arctic and Alpine Research, Vol. 18, No. 1, 1986, pp. 1-17 RESPONSE OF PERMAFROST TERRAIN TO DISTURBANCE: A SYNTHESIS OF OBSERVATIONS FROM NORTHERN ALASKA, U.S.A. DANIEL E. LAwson U.S. Army Cold Regions Research and Engineering Laboratory 72 Lyme Road, Hanover, New Hampshire 03755-1290, U.S.A. ABSTRACT Former exploratory drilling sites in the National Petroleum Reserve-Alaska, are examples of the long-term physical modifications resulting from disturbance of perennially frozen terrain. Camp construction and drilling activities in the late 1940s/early 1950s resulted in disturbances which can be grouped by their first modification to the site and its thermal regime: trampling of vegetation, killing the vegetative cover, removal of the vegetative mat, or removal of the vegetation and soil. Removal of the vegetation led to the most extensive modifications at all sites, but the subsequent response to disturbance between sites varied with primarily four factors: (1) ground ice volume, (2) distribution and size of massive ground ice, (3) material properties during thaw, and (4) relief, including progressive changes during thaw subsidence. Variations in response time resulted from the influence of these factors on the type and activity of degradational processes that ensued. Terrain underlain by ice-poor sediments that are stable upon thawing, for example, was altered only by thaw subsidence and consolidation, while ice-rich sediments that are unstable at thaw were extensively modified by a complex interac- tion of slumping, sediment flow, and thermal and mechanical erosion. Drainage promoted meltwater erosion, whereas undrained areas were modified significantly less and attained stability more rapidly. Physical stability is required for growth of vegetation and thermal equilibration, and has taken over 30 yr to attain in ice-rich, thaw-unstable areas. Ice-poor, thaw-stable materials in undrained or low relief areas required an estimated 5 to 10 yr for stability; thaw depth measurements suggest that certain of these areas have also equilibrated thermally. INTRODUCTION The long-term effects of human impact on arctic ter- rain underlain by permafrost are not well understood. An understanding of these effects is needed for a realistic ap- praisal of the terrain’s sensitivity to development, and thus for assessing potential methods to prevent unwanted environmental changes. Former drill sites in the Naval Petroleum Reserve Num- ber 4 (PET-4, Figure 1), now designated the National Petroleum Reserve-Alaska (NPRA), are examples of the effects of camp construction and drilling operations on perennially frozen sediments and terrain after approxi- mately 30 yr. Thirty-six exploratory wells were drilled in PET-4 by the U.S. Navy from 1944 to 1953 (Reed, 1958). These drilling sites lie within several different geologic, topographic, and climatic settings of the North Slope region. From 1978 to 1982, I examined the long-term effects of disturbance at 10 sites, three intensively, with the intent to (1) define physical changes in the near-surface mate- rials and terrain resulting from camp construction and drilling activities, (2) define the degradational processes that modified the site to its present condition, and (3) D. E. Lawson / 1 evaluate the physical properties that determined spatial and temporal variations in the site modifications. Attain- ing this final objective would indicate potential param- eters or criteria for identifying and possibly mapping ter- rain sensitive to disturbance. In this paper, I summarize certain aspects of this re- search and discuss its implications for the recovery of permafrost terrain to disturbance, including the time over which it may take place. Details of this research are in- cluded in Lawson (1979, 1982, 1983), Lawson and Brown (1979), and Lawson et al. (1978). FIELD SITES The three sites studied in detail were Fish Creek, Oumalik, and East Oumalik (Figure 1). These sites were last occupied in 1949, 1950, and 1951, respectively. Their geology and morphology are summarized in Table 1. In general, the immediate area upon which each exploratory well was located had little relief, ranging from about 0.5 to 2 m. Surficial materials were reasonably uniform in composition and texture (generally silt or sand). The un- disturbed active layer thickness typically ranged from about 0.3 to 0.4 m. These sites were chosen for detailed studies because sev- eral characteristics common among them simplified com- paring the effects of disturbance: (1) Each site was occupied for approximately one year and last occupied about 30 yr ago. (2) Construction methods, drilling activities, equip- ment, buildings, and vehicles used at each site were essen- tially the same. (3) None of the sites had been affected significantly by man’s activities before the PET-4 drilling program. METHODS I used standard geological techniques to analyze the response of each site to disturbance. Details of the surfi- cial geology of the disturbed areas were defined mainly by field and laboratory analyses of equivalent undisturbed areas that were identified by comparing aerial photo- graphs taken in 1948 with photographs from 1977 or 1978. Because no observations had been made between the time when the three sites were abandoned and when this study was begun, the degradational processes had to be interpreted from the morphology of the modified ter- rain and the sedimentology of deposits of the degrada- tional processes. Whenever possible, trenches were dug to examine the sedimentology of disturbed and undis- turbed near-surface materials. Surficial materials in the active layer and the peren- nially frozen ground underlying disturbed and undis- turbed areas were sampled by coring. Drill holes were located upon representative surficial features and along transects across disturbed and undisturbed terrain. A total of 120 holes were cored to depths ranging from 1.5 to 43 m. An additional 450 holes of 1.5-m depth and spac- ing of 2 m were augered along several transects across each site. All transects, as well as the topography of dis- turbed and undisturbed areas at each site, were surveyed using a self-leveling level or theodolite. Details of the drill- ing equipment and methods of coring are described in Lawson and Brockett (1980) and Brockett and Lawson (1985). The geology of each drill hole, including the type and distribution of visible ground ice, was logged. The active layer thickness was determined by probing with a steel rod at various times during the summer season, and ground temperatures were measured in selected boreholes with a thermistor calibrated to +0.01°C. Frozen and thawed samples were selected for laboratory analyses fol- 2 / ARCTIC AND ALPINE RESEARCH lowing standard procedures that included grain size dis- tribution, moisture content, ice volume, organic content by loss on ignition, bulk density, and liquid and plastic Atterberg limits. These data were used to calculate various material properties such as degree of saturation, porosity, void ratio, and textural statistics. ARCTIC OCEAN Camp Beaufort Seo Chukchi Sea 162 O° 18" 156° 154° 132 Ficure 1. Map of the NPRA region locating East Oumalik, Oumalik, and Fish Creek in northern Alaska. DISTURBANCE AND RESPONSE The types of disturbance—camp activities and con- sediment with the vegetative mat (Table 2). Each type of struction —can be categorized according to the first physi- disturbance is described in detail and illustrated in Law- cal modification they caused. These categories are (1) son et al. (1978) and Lawson (1982). trampling and compaction of the organic mat including The physical response at each site differs according to the living vegetation, (2) killing of vegetation, (3) removal the degree that the thermal regime of the affected area of the vegetative mat, and (4) removal of near-surface is altered by each disturbance type. A modified thermal TABLE | Summary of site geology and physiographic setting of the East Oumalik, Oumalik, and Fish Creek drill sites Physiographic Near-surface Site province materials Geologic origin Relief Fish Creek Arctic Coastal Plain Fine- to medium-grained Camp and exploratory Maximum local relief (70°19'15"N, sand, minor silt layers _ well lie on stabilized about 5 m; on site, 151°58'08" W; eolian sand dunes; <ilm. elev. 5.1 m) drained lake basins lie adjacent to site; small stream valley to west. East Oumalik Arctic Foothills Coarse-grained silt; Site on upland com- Maximum local relief (69°47'29"N, minor sand lenses posed of loess (silt de- about 15 m; on site, 155°32'39’W; posited by eolian pro- <2 m. elev. 84.4 m) cesses); stream valleys on N, W, and S sides. Oumalik Arctic Foothills (near Coarse-grained silt; Well site located in Maximum local relief (69°50'18"N, northern limit) occasionally fine- to drained lake basin. about 4 m; on site, 155°59'24" W; medium-grained sand Camp located on adja- <3 m; on well site, elev. 52.6 m) cent knoll of upland silt <0.5 m. reworked by lake pro- cesses. TABLE 2 Classification of disturbance by activities and their initial modification to vegetation, soils, and sediment Type of disturbance Initial modification Types of activities 1 Trampling and compaction of vegetation a. Off-road vehicle movements, single and multiple passes by wheeled and ski-mounted vehicles. . Snowpads (e.g., winter trails). Footpaths. Temporary storage of supplies. 2 Killing of original vegetation Hydrocarbon spills (diesel fuel, crankcase oil). Boardwalk and elevated buildings. Solid waste (e.g., steel drums, tarps, woodpiles, nondegradable waste). Berms (spoil piles) formed along bulldozed trails and excava- tions. Shallow bulldozed roads. Shallow excavations for building foundations. Piling (local). Tracked vehicle movements. Bulldozed roads. . Excavation of trenches, drainage ditches, and sump. c. Basement excavations for drill rig piling. esp BOS 2. 3 Removal of vegetative mat Be oP 4 Removal of near-surface sediment with vegetative mat oP D. E. Lawson / 3 regime can be interpreted from depth of thaw measure- ments in disturbed and equivalent undisturbed areas. Al- though the modifications resulting from a particular dis- turbance type differ in severity from site to site, the rela- tive amount of physical change resulting from each type is similar at the three sites. The removal of the vegeta- tive mat, which insulates the permafrost, led to extensive and apparently permanent changes in each site’s physical characteristics and thermal regime. In contrast, a slight trampling or killing of the vegetation resulted in little sig- nificant long-term physical modifications in most instances, and only slightly modified thaw depths. Com- paction of the vegetation resulted in different degrees of change, varying with the intensity of compaction and also its immediate effects upon drainage. In nearly every in- stance, some site changes took place after compaction that affected the morphology of the terrain or properties of near-surface sediments, while increasing the thickness of the active layer. This increase in the depth of thaw is, however, usually significantly less than that in areas dis- turbed by the removal of vegetation. The results of these studies indicate that the actual removal of the vegetation or surficial materials is critical to the extent that lasting physical modifications take place. A brief synopsis of the physical response of each site to disturbance can be considered in terms of major land- forms. Ficure 2. Aerial photograph of Fish Creek site before disturbance (BAR 741-030, 7/10/48). Lines indi- cate general position of drilling transects. Landforms on site include (1) upland sand dunes, (2) drained lake basins, and (3) stream valley and floodplain. North to top. 4/ ARCTIC AND ALPINE RESEARCH FisH CREEK The Fish Creek site is located on the Arctic Coastal Plain, approximately 28 km south of the Beaufort Sea (Figure 1). The regional terrain varies from flat to gently rolling and numerous thaw lakes and drained lake basins cover the area (Figure 2). Moderately drained dune ridges or uplands separate poorly drained and undrained depres- sions. Small meandering streams, such as the one next to the Fish Creek site, flow in relatively narrow valleys that locally show relief of about 5 to 10 m. The Fish Creek drill site lies mostly on a well-drained, dunal upland adja- cent to three drained lake basins (Figure 3). Unconsoli- dated and well-sorted, fine-to-coarse-grained sand of Quaternary age underlies the region. Polygonal ground is common on both the drained lake basins and upland surfaces (Figure 2). Upland Sand Dunes The camp and drill pad were located on the upland next to the drained lake basin (Figure 3). The upland surface had little relief, with moderate drainage and thaw depths in the range of 0.2 to 0.4 m before disturbance. After 30 yr, the camp area is hummocky, although mounds and depressions are of low relief (max. about 2 m), with stand- IDEALIZED STRATIGRAPHY AND LANDFORMS Ficure 3. Schematic diagram illustrating the stratigraphy and landforms of the Fish Creek site. Drill rig and camp were set (Fish Creek) West Drained East Stream Dunal Lake Ounal Es 10 Valley Upland Basin Upland Drained Lake Basin 7 Ea Be o 2 a= 2 58 0 go <2 cw oS =3 S219 os | L L 1 | on I ! Jeu | 1? > ° 200 400 600 800 1000 1200 1400 Distance (m) 24 Alluvium ==Isir ®,® | Colluvial | Siope Deposits ZZ tee Sill Locustrine Deposits VV V0 Ice Wedges Eolian Sand = — Ice Lenses 0°00] Fluvial ?/Marine ? yaNwA Sedimentary 2° }Sand Bedrock up on the dunal upland. Ficure 4. Aerial photograph of the Fish Creek site in 1977. Physical changes occur only where the terrain was actually disturbed. Representative loca- tions disturbed mainly by activi- ties of the four disturbance types (Table 2) are indicated by numbers | through 4. No. 3 on Figure 2 is indicated by X. D. E. Lawson / 5 ing water in the 0.5- to 1.0-m-deep depressions and modi- fied thaw depths ranging from 0.3 to 0.8 m in July (Fig- ure 4). Depressions with a polygonal pattern developed as ice wedges beneath the upland melted. Thaw subsi- dence was generally limited to about 0.5 m, attaining a maximum in areas where bulldozing removed the vegeta- tive mat, melting ice wedges (about 1.0 to 1.5 m). Shallow gullies developed in the upland where excavated drain- age ditches flowed into the adjacent lake basins or the stream valley. Thermal and hydraulic erosion were re- sponsible for their formation. Except for small ice wedges (1.1 to 2.4 m by 1.5 to 3.2 m), only pore ice and rarely lens ice are present in the dunal sand beneath the site. Drained Lake Basin A large basin to the east of the site was disturbed mainly as the result of the drainage ditches that emptied into it (Figure 4). Meltwater flowing from the site caused thermal and mechanical erosion. Subsidence and erosion created gullies up to 2 m deep. The segregated ice con- tent of the lake sediments was greater than that of the upland sand, resulting in slightly more thaw subsidence. Maximum areas of subsidence were located above melting ice wedges, which were of similar dimension to those in the upland; these depressions contained standing water during the summer. Thaw depths ranged from 0.3 to 0.9 m in July. Ficure 5. Aerial photograph of East Oumalik before disturbance (BAR 124-147, 9/6/48). Lines indi- cate general location of drilling transects. Upland silt (1) and valley slope (2) are located. North to top. 6 / ARCTIC AND ALPINE RESEARCH Stream Valley A small beaded stream on the west side of the site flows within a valley of about 100-m width and 5-m depth. Physical degradation is generally limited to upper valley slopes where channelized meltwater eroded gullies up to 2 m deep, and in one case, deposited a small alluvial fan at the base of the valley slope. The valley bottom shows few modifications and is the least altered area of the Fish Creek site. Only pore ice is present in the frozen alluvial and valley slope deposits. EAsT OUMALIK East Oumalik is located in an area of upland surfaces cut by meandering streams and active, often deeply incised, thaw lakes (Figure 5). Maximum relief locally is about 20 m. The drill site was located upon an upland surface composed of a relatively homogeneous silt of Quaternary age that overlies sedimentary bedrock at a depth of 24 to 39 m (Figure 6). The ice-rich upland silt is interpreted to be a wind-blown silt or loess. Upland The undisturbed upland is moderately drained, with a surface of low relief (<2 m) and a gentle slope toward the west and toward the stream valleys on the north and south (Figure 6). Relatively little standing water is present. Disturbance by construction and camp activities has re- sulted in extensive modification of the terrain. The ground surface is now hummocky, with numerous deep depressions (Figure 7); maximum relief across the site is about 8 m and individual depressions are up to 5 m deep. Water remains standing in some depressions year-round and snow often remains in deeper depressions late into the summer season. In general, the moisture regime and drainage have been modified from relatively uniform to highly variable with significantly wetter and drier areas present. Areas undergoing thaw subsidence with drain- age down the valley slopes were thermally and mechani- cally eroded by flowing meltwater. Although depressions on the upland initially developed as wedge ice melted, mass movements and other forms of lateral slope erosion modified their shape and increased their size beyond that of the ice wedges and the area of disturbance. Regardless of the disturbing activity, disrup- tion of the vegetative mat initiated rapid and laterally ex- panding degradation beyond the actual area of disturb- ance into the adjacent undisturbed parts of the site. Large ice wedges (5 to 10 m wide, 7 to 14 m deep) and other forms of segregated and massive ice are common and facilitated the lateral spreading of thermal and physical modifications to the upland. Valley Slopes Slopes between the upland surface and streams are characterized by an upper section of low angle (~ 10 to 15°) and a lower section of higher angle (~20 to 25°) which is covered by apparently inactive solifluction lobes (Figure 6). Total relief along the length of the valleys near the site varies from 3 to 15 m. Disturbance was localized and resulted mainly from off-road vehicles moving be- tween the upland camp site and the streams. Response of the slopes to the vehicle movements varied, with upper slopes undergoing significant thaw subsidence and lower slopes very little change. Excavated drainage ditches on the valley slopes showed a similar response, with the maximum deepening (about 2 to 3 m) and lateral expan- sion beyond the original dimensions of the ditch occur- ring in the upper slope. The difference in response appears to relate directly to the difference in ground ice volume; the upper slope materials typically contain 50% more ice than the lower slope materials. A Be North South Stream Valley Valley || le Slope Upland Slope and Terraces Ex 7 ee oe os 25 $f 38 ae su IDEALIZED STRATIGRAPHY AND LANDFORMS. 3S 3 {East Qumatik) Se West East YS Stream Valley Valley -20U ! : | L : ES and Terraces’ Slope Upland ° 200 400 600 800 1000 a2 = Distance (m) 5 50 Lt TT] ye] Alluvium ==] sit 9% 20 T= = © 2 20 oth = -® | Colluvial Ice Sill 3 & 108 © YY @ | Slope Deposits 23° LO @ AMM Lacustrine UP Tce wedges 5" op Bn ERIN TNT NT NIN TRINA ST NINN Pr aeRO NV RTE TRIO Deposits vy 9 S=-1 58 : ; } \ Eolian Sand © = Ice Lenses z 3 ° 500 1000 1500 2000 [oo 0] Fluvial ?/Marine 2? yy Sedimentary Distance (m) 2°} Sand Bedrock Ficure 6. Idealized cross sections of the stratigraphy and landforms at the East Oumalik site. The camp and drill rig were set up on the upland surface. (A) illustrates the long-axis stratigraphy, (B) lies perpen- dicular to the long-axis between the two stream valleys. The ice sill is a massive body of ice whose origin is under investigation. D. E. Lawson / 7 Valley Bottoms and Stream Terraces Little change was observed to the relatively flat terraces or active floodplain of the streams. Where ice wedges were disturbed by vehicle traffic, thaw subsidence of 0.5 m or less took place. Very low ice volumes, small ice wedges, and the coarse-grained size of the alluvial de- posits appear largely responsible for the absence of thermokarst. OUMALIK Oumalik, located about 18 km west of East Oumalik (Figure 1), is an area principally of coalesced, drained thaw lake basins, many of which contain or are separated by remnants of uplands similar to those at East Oumalik (Figure 8). The lake basins are poorly drained and are covered by polygonal ground. Silt beneath the uplands at Oumalik is physically and mineralogically similar to that at East Oumalik and believed to be contemporaneous wind-blown material derived from the same source. Drained Lake Basin The drill pad and associated equipment were located in a basin that is generally poorly drained and contains shallow pools of water (Figure 9). On site, relief is limited to that of the polygonal ground and is less than 0.5 m. The effects of disturbance were limited, with most changes in relief actually caused by the removal and mounding of material by bulldozing. Thaw subsidence may account for about a 0.3- to 0.5-m change in eleva- tion, with differences of 1 to 2 m between the tops of mounds and bottoms of excavated depressions or trails. Thaw of wedge ice developed distinct, polygonal depres- sions with depths today of about 1.5 m or less. Bulldozed trails are very wet, with standing water and a beaded con- dition at locations where wedge ice melted (Figure 10). The polygonal pattern to the wedge troughs, which is ap- parent in aerial photographs taken prior to disturbance, is now simply enlarged in dimension and commonly filled with standing water. In wet areas, thaw depths in late summer (~45 to 55 cm) approximate those in adjacent, undisturbed parts of the drained basin; however, in the drier mounds, thaw depths late in summer exceed those values by up to 30 cm. Beach Ridge This ridge or knoll is well-drained by comparison to the basin area (Figure 9) and was one reason why the camp was located here. A boardwalk connected the drill site to the camp area. The knoll stands about 5 m higher than the basin area and has a fairly gentle slope to the east and west (Figure 9). Distubances from camp con- struction and drilling activities have significantly modi- fied the ground surface, mainly as the result of melting of ice wedges after thermal regime modification, and thermal and mechanical erosion as meltwater from ground ice flowed within the subsiding troughs toward the drained lake basins. The hummocky surface (Fig- ure 10) commonly has water standing within troughs, par- ticularly at former wedge intersections on the upper knoll surface. Hummocks exhibit a rounded form and poly- gonal pattern to adjacent troughs. Elevation differs be- tween mound and trough surfaces by 1.5 to 2 m. Thaw depths in late summer average 80 cm in the mounds, whereas they are about 40 cm in undisturbed sections of the knoll. Ridge Slopes Prior to disturbance, the surface of the ridge slopes ex- hibited little relief, with only shallow, straight ice wedge troughs on these surfaces fanning radially away from the ridge axis toward the basin. After disturbance, gullies about 1 to 2 m in depth were mechanically and thermally Ficure 7. Aerial photograph of the East Oumalik site in 1978. The entire site is covered by high relief thermokarst, including areas that were not disturbed, but which lay adjacent to disturbed terrain. Numbers 1 through 4 locate areas initially disturbed by activities of mainly types 1 through 4 (Table 2). End of transect line on Figure 5 is indicated by X. 8 / ARCTIC AND ALPINE RESEARCH eroded by meltwater flowing off the degrading ridge. Alluvial fans were deposited at the base of each slope on the edge of the drained lake basin. Erosion, however, ended abruptly at the change in slope on the basin’s edge. IMPACT COMPARISON As a simple, somewhat subjective comparison of the physical effects of disturbances on the terrain of each site, I have computed a severity index (S;) of disturbance as a ratio of the final area of impact (A,.) to the initial area of disturbance (A,2): Si = Aja/Aia (ql) The disturbed area (A;.) is defined as an area affected by some disturbance (e.g., the area of tracks of a wheeled vehicle). The impacted area (A,,) is an area that is physi- cally modified in response to that initial disturbance. These values are subjective because areas only slightly dis- turbed were often difficult to identify on the ground or in aerial photographs, while it was sometimes difficult to define the original area of disturbance in areas exten- sively modified following that disturbance. Thus, for S;=1.0, the impacted area equals the area initially disturbed. For S;>1.0, the impact of disturbance has spread beyond the area that was affected by a dis- turbance. Values of S;<1.0 indicate that the effect of a disturbance was not permanent and thus some recovery occurred to return the area to its previous condition. In Table 3, values for S; at Fish Creek, Oumalik, and East Oumalik are compared for the four general types of disturbances. Typical depths of depressions resulting Ficure 8. Aerial photograph of Oumalik before disturbance (BAR 106-117, 9/4/48). Lines indicate general position of drilling transects. Upland (1), drained lake basins (2), and knoll (3) are located. North to top. D. E. Lawson / 9 from thaw subsidence and related degradational processes following disturbance are also listed. Values for S; mea- sured at East Oumalik (0.9 to 2.6) were generally much larger than those at Fish Creek (0.9 to 1.2) or Oumalik (0.8 to 1.9). At all sites, removal of vegetation and soil led to the most severe impacts and deepest depressions. Physical recovery occurred only where the initial disturb- ance was a compacting of the vegetation, such as from single passes of tracked vehicles. A similar recovery was observed by Abele et al. (1984). The areal extent of impact usually covers or extends beyond the boundaries of the original disturbance on the East Oumalik site, whereas it is most often limited to within the individual areas actually disturbed at both Fish Creek and Oumalik. DEGRADATIONAL PROCESSES AND CRITICAL RESPONSE FACTORS The differences in the extent of modifications and the rate of change in the physical and thermal characteris- tics of each site are directly related to (1) the volume of ice in near-surface materials, (2) geotechnical properties of surficial materials during thawing, (3) distribution and dimensions of massive ground ice, and (4) relief, includ- ing progressive changes in it as thaw subsidence took place following disturbance. These factors, in turn, determine the types of degra- dational processes that become active and thus the condi- tions necessary for a physical stability to eventually de- velop. Physical stability is important since it is necessary for (1) attenuation of the increasing depth of thaw and hence development of a thermal regime that is in equi- librium with the modified physical conditions, and (2) the establishment of a permanent cover of vegetation. This latter condition is complex, because once vegetation can establish itself on ground that may be minimally stable, its presence and root growth can help stabilize the physi- cal and thermal regimes. Idealized sequences of degradational processes, includ- ing variations in ground ice volume and type, local relief, drainage, and relative intensity of disturbance, are shown TABLE 3 General comparison of physical modifications to terrain at East Oumalik (EO), Fish Creek (FC), and Oumalik (O) drill sites due to disturbances as grouped in Table 2 S; Depth of Initial (severity depressions disturbance Site — index)* (m) 1. Trampling and compaction EO 1.0 -1.43 0.7-4.2 FC 0.9 -1.0 0.1-0.7 oO 0.8 1.0 0.2-0.6 2. Killing vegetation EO 1.0 -1.1 0.1-1.1 FC 1.0 Up to 0.2 oO 1.0 Up to 0.3 3. Vegetation removal EO 1.7 2.6 3.1-5.5 FC 1.0 -1.2 0.2-1.5 OO. 1.1 -1.7 0.3-2.0 4. Sediment and vegetation EO 1.25-2.5 3.0-5.0 removal FC 1.0 -1.2 0.4-2.0 Oo 1.1 -1.9 0.5-2.0 4§, represents areal effects as defined in the text. IDEALIZED STRATIGRAPHY AND LANDFORMS (Oumalik) West East a Drained EX 5;-Lake Basin Knoll Drained Lake Basins Slope Upland e2 OF a ale = af tree eee Sec (slope) (upland remnant) sanunaeaneaal i. cna oy ls se ' (older) ' (younger) ! | 23 0 | os 5 BoD FE aoe ae. 1 ew . =| 23 32 oT 26 w> pESEED = 1 Alluvium =I sur Colluvial I (eet Stope Deposits ZZ Tee 5 Locustrine 0 L Ages PVVE Ice Wedoes Eotion Sond 2 = Ice Lenses [OSo] Fluviol F/Morine ? PORWR Sedimentary Lee } song Bedrock 800 Distance (m) Ficure 9. Idealized cross section of the stratigraphy and landforms of the Oumalik site. Drill rig and platforms were set up in the large drained lake basin while the camp was constructed on the knoll. 10 / Arctic AND ALPINE RESEARCH schematically for each site in Figures 11, 12, and 13. Degradational processes were most complex and interac- tive at East Oumalik, and least on the dunal upland at Fish Creek and within the drained lake basin at Oumalik. While physical stability and an active layer thickness com- mensurate with the site’s modified condition have ap- parently developed over much of the Fish Creek site and within the drained lake basin at Oumalik, the upland at East Oumalik basically remains physically and thermally unstable, with seasonal thaw depths considerably exceed- ing those in undisturbed areas and being widely variable. The camp area on the ridge at Oumalik appears to have stabilized physically, but with an active layer that is thicker than in equivalent undisturbed terrain. Comparison of the in-situ material properties in undis- turbed areas (Table 3) indicates that several basic prop- erties affecting their stability or resistance to failure and erosion differ between the three sites. The effect of thaw- ing, for example, differs. The ice-poor sand at Fish Creek will have a significant frictional resistance to shear at thaw, and thus a significant shear strength and resistance to failure (Table 4). In contrast, the ice-rich silt at East Oumalik is generally unstable at thaw and highly suscep- tible to failure and mechanical erosion. Oumalik mate- Ficure 10. Aerial photograph of the Oumalik site in 1978. Polygonal wedge troughs in the drained lake basin (a) have been deepened, with the beach ridge or knoll (b) most heavily dissected as the result of thermal and mechanical erosion by water moving within troughs above melting ice wedges. Areas disturbed mainly by the activities of the four disturbance types are indicated by numbers 1 through 4. Knoll (b) appears as knoll (3) on Figure 8. North to upper right corner. D. E. Lawson / 11 Typical path for upland areas with low ice content and local, low intensity disturbance Initial disturbance of surface 4 Thermal alteration of vegetation and soils; Increasing seasonal depth of thaw Thaw bulb growth with thaw subsidence Pooling of water; reduced thaw bulb expansion rate | Typical path for upland areas and drained lake basins with wedge ice; most areas disturbed by removal of vegetation and soils Path for sloping disturbed surfaces Differential subsidence above melting wedge ice; local melt- water erosion Differential thaw subsidence; thickening of thawed sediment layer; partial revegetation Channelized water flow; thermal and mechanical erosion of chan- J nel bed Path for closed thaw depres- sions with wedge ice and lateral banks of low ice content Complete revegetation; season- al thaw depth equilibrating Thaw bulb expansion; failure and/or erosion of slope materi- als; thaw subsidence Lateral slopes may fail by slump, grain flow/creep; sediment ac- cumulates at base of slope | 4 Loss of gradient and/or water source, slope material accumu- lates in depressions; decreased thaw bulb expansion Thawed layer thickens; decreased thaw bulb growth } | Thickening of thawed sediment layer; reduced slope angle; par- tial revegetation Partial revegetation on base of slopes and within depressions; upper slopes stabilizing; local thaw subsidence | 1 Complete revegetation; season- al thaw depth equilibrating; thaw consolidation Complete revegetation; season- al thaw depth equilibrating; thaw consolidation 1 vy Thermal equilibrium fee ee Ficure 11. Schematic process-response flow chart illustrating common sequence of processes that caused modification of the dunal upland and drained lake basin at the Fish Creek site. Dashed line indicates sequence not completed at time of this study. Sequential changes in vegetation based upon flow charts of Bliss (1970) and Komarkova and Webber (in Lawson et al., 1978). Physical effects expanded and modified from general flow chart of Mackay (1970). 12 / ARCTIC AND ALPINE RESEARCH rials vary in ice content, but are mostly susceptible to ero- sion and failure. Locations within the drained lake basin and in the upper part of the knoll at Oumalik contain sufficient segregated ice so that the silts are generally over- saturated upon thawing, with water contents above their liquid limits. In the knoll slopes, however, the reworked silts contain less ice. Because the drained lake basin at Oumalik is generally wet with standing water common in summer, thawed material in the lake bed will be con- stantly oversaturated and may be subject to subaqueous readjustments of the silt under the force of gravity. Typical path for areas with low er ice content, small bodies of Initial disturbance of surface depth of thaw a Thermal alteration of vegetation and soils: increasing seasonal ice, and local low intensity dis: turbance Pooling of water, reduced thaw bulb expansion rate _ _| subsidence ee Thaw bulb growth with thaw and soils Path for sloping disturbed surtaces Path for thaw depressions with massive Ice and lateral banks of high ice content Differential thaw subsidence. thickening of thawed sediment layer; partial revegetation Channelized water flow: ther mal and mechanical erosion of channel bed | ae Lateral slope instability devel oping with deep differential thaw subsidence Failure of lateral banks by slump and sediment flow: melt water erosion of bank surfaces permatrost exposed in banks Typical path tor areas with high ice content massive ice: most areas dis. turbed by removal of vegetation including large Volumetrically, ice composed 35% more of the near- surface sediments (upper 5 m) at East Oumalik than at Fish Creek, and up to 20% more than at Oumalik (Law- son, 1983). In addition, massive ground ice (wedges, lenses) may compose up to 60 to 70% of the upper 10 m of surficial materials at East Oumalik, whereas at Fish Creek it was about 10 to 15%, and at the Oumalik site an estimated 30 to 40% (Lawson, 1983). The large ice volume at East Oumalik reflects both the large dimen- sions of ice wedges and the numerous ice lenses and seg- regated ice forms that occur in the silt. At Oumalik, the Path for closed thaw depres: sions with massive ice and la teral banks of low ice content Melting of massive ice; steep la teral slopes develop: perma: frost exposed J Thaw bulb sion: lateral Lateral expansion of depres. Lateral slopes fail by slump or Complete revegetation: season. | slope failure: removal of slope ‘sio by mass Ing: slope spalling: differential thaw rates al thaw depth equilibrating | colluvium by meltwater erosion. lluvium accumulates in sub: enhance spalling: sediment ac thaw subsidence siding depressions umulates at base of slope — - 1 Banks now ' ! oss of gradient andio 1 jeduce nin Loss of gradient andior wate Reduced layer thickens: differen 1 source. sl us depre base 1g of slope: spalling 1 lates essions: decreased reduced slope angle as upper 7 s ° decreased thaw bulb growth 1 | ulb expansion bank continues mass wasting grow! I l L } Thic aye failut 1g of thay sation o} J sic Partial rev upper steep slope stab! revegetation on base of 4 within depressions: pes stabilizing: local thaw subsidence ) Complete revegetation: season. al thaw depth equilibrating, thaw consolidation Revegetation complete: season al thaw depth equilibrating thaw consolidation Revegetation complete: season. al thaw depth equilibrating: thaw consolidation Complete revegetation: season al thaw depth equilibrating thaw consolidation ¥ aseeeseennD>) Thermal equilibrium FicurE 12. Schematic process-response flow chart illustrating common sequence of processes that caused modification of the basin area near the exploratory well and the ridge or knoll upon which the camp was located at Oumalik. Dashed line indicates process sequence not completed at this time. D. E. Lawson / 13 more heavily disrupted ridge contained larger ice wedges within the sediments, while the less intensely disturbed basin area had much smaller wedges and slightly less segregated ice. An additional factor affecting impact intensity is the relief. At Oumalik, the slope of the ridge resulted in con- centration of meltwater flow along polygonal troughs, with subsequent downcutting, lateral expansion, and headward erosion of the gullies into the upper ridge sur- face. In contrast, the basin area at Oumalik is very poorly Pi 4 Initial disturbance of surface | Mt Thermal alteration of vegetation and soils; increasing seasonal | depth of thaw l Typical path for areas in basin with lower ice content, 5 — | Pooling of water, reduced thaw bulb expansion rate, subaque ‘ous movements in sediment | J at Differential thaw subsidence. | thickening of thawed sediment layer; partial revegetation Thaw bulb growth with thaw subsidence Path for sloping ridge surface posed subsidence / | Complete revegetation; season | Channelized water flow: thermal | | and mechanical erosion of chan Melting of wedge ice; lateral slopes develop; permatrost ex yp Failure of lateral banks by slump and sediment flow; meltwater drained and just the opposite effect occurred. Standing water, coupled with the saturated state of the sediments, led to only localized movement of thawing sediment. Relative stability of the thawed sediment was probably reached here much faster than in most other landforms on the three sites. The lack of slope on the Fish Creek upland likewise minimized the flow of meltwater from thaw depressions. Relief was an important factor at East Oumalik; the connection of the slope drainage system with that which developed on the thermally and physi- Typical path for areas in ridge and in basins with higher ice content and wedge ice Path for closed thaw depres sions in basin with wedge ice ~~ Path for thaw depressions on J¢—________ ridge: moderate ice content in 7 —! lateral slopes be at Lateral slope instability devel ‘ops with deep differential thaw Lateral slopes fall by slump or tlow (some subaqueous); sedi ment accumulates at base of | slope Thawed layer thickens; ditteren. tial thawing of slope; decreased al thaw depth equilibrating erosion of bank surface; perma thaw bulb growth Tho | nel bed J ue 5 um ie Tal reel ot so jacent depressions to slope area Patani ei and drainage develops TT Loss of gradient andlor water source: slope material accumu: lates in depressions; decreased thaw bulb expansion nr Thickening of thawed sediment layer. cessation of lateral slope failure; reduced slope angle; | partial revegetation i Complete revegetation season althaw depth equilibrating;thaw consolidation frost exposed in banks w bulb expansion: lat Literal seponsiil condits 8a Lateral expansion of depres sions by mass wasting: slope colluvium accumulates in sub: siding depressions | Partiai revegetation as depres sions and slopes stabilize; local slope adjustments; thaw subsi dence Bit Reduced thaw bulb growth in depressions and at slope base; reduced slope angle as upper bank continues mass wasting Sea Partial revegetation on base of slopes and within depressions: upper slopes stabilizing: local thaw subsidence ii + Revegetation complete; season: althaw depth equilibrating; thaw consolidation Thermal equilibrium - | aula | Complete revegetation, season. althaw depth equilibrating; thaw consolidation Ficure 13. Schematic process-response flow chart illustrating the common sequence of processes that caused modification of the East Oumalik upland. Dashed line indicates process sequence not completed at this time. 14 / ArcTIC AND ALPINE RESEARCH cally degrading upland enhanced the degradational pro- cesses on the upland by removal of both meltwater and eroded sediment. Thus, in terms of physical modifications, the most drastic changes took place where thaw-unstable sediments containing large volumes of segregated ice were associated with large bodies of massive ice and where drainage de- veloped to permit rapid removal of meltwater and eroded sediment. Under these conditions, lateral slopes of thaw depressions were unstable and gravitational slope pro- cesses laterally expanded degradation into adjacent undis- turbed sediments. This situation is exemplified by East Oumalik. The least amount of change occurred where all forms of ground ice were limited in dimension and distribution, drainage was inhibited, and sediments were thaw-stable. Under these conditions, the processes of thaw subsidence and subsequently thaw consolidation were predominantly active. The upland at Fish Creek and the wet, drained lake basin at Oumalik exemplify this situation. Factors which may have had some effect on the extent and rapidity of modification are the differences in cli- matic parameters between the more coastal, and presum- ably maritime influenced Fish Creek site, and the inland Oumalik sites. The effect of climate could not be ade- quately addressed in these studies. Limited climatic data (Haugen and Brown, 1980) suggest that the mean annual temperature may differ by 1°C, with a greater number of thawing degree days inland. Other parameters, such as input of solar radiation and precipitation, are virtually unknown. On the basis of this study, however, the volume and extent of ground ice, relief, and material properties appear to be the predominant factors resulting in the dif- ferences in physical modification between sites. MODIFICATION AND RECOVERY Physical modifications will cease only after the increase in the seasonal thaw depth that results from disturbance of the thermal regime ends, and the secular depth of thaw remains stable or decreases with time. The thaw depth will stabilize as a sufficiently thick insulating layer of thawed sediment develops, either as the simple result of the increase in depth of thaw or from the deposition of reworked sediments over the disturbed area. Growth of vegetation and development of a thick mat of organic material subsequently aid and maintain the thermal bal- ance. As thawing is reduced, less meltwater is produced, which reduces the potential for fluvial erosion and the susceptibility of the thawed sediment to either failure or erosion. Thaw consolidation of the thawed layer is the last material alteration before physical stability. The thermal regime which finally develops will ultimately reflect the modified physical conditions. The disturbances caused by construction and drilling operations have led to significant physical modifications of each site, as well as others in PET-4 (NPRA). The long- term effects or modifications to each sites’ physical con- dition appear to be quite permanent (within man’s time TABLE 4 Summary of selected properties of near-surface sediment from undisturbed and disturbed locations at the East Oumalik, Fish Creek, and Oumalik drill sites East Oumalik upland upland Fish Creek Oumalik beach ridge Oumalik drained lake basin Undisturbed Disturbed Undisturbed Disturbed Undisturbed Disturbed Undisturbed Disturbed Grain size (¢) m 5.50 m 5.50 m 2.75 (mean-m, std. 01.2 01.2 o 0.7 dev.-o) Moisture con- 80-250 40-120 19-71 tent (% dry wt) (sporadically to 120%) Ice volume (%) 60-100 40-65 23-68 (excludes ice (m 85) (m 47) wedges) Degree of 0.95-1.2 0.8-1.1 0.6-1.05 saturation (m 1.05) (m 0.96) (frozen) Bulk density 0.9-1.6 1.6-1.8 1.5-2.2 (g cm”) (m 1.2) (m 1.65) (m 2.0) Dry density 0.3-1.1 0.8-1.2 1.4-1.8 (g cm™) Void ratio 3-14 0.5-2.8 0.4-1.61 Liquidity index 1.6->15 0.9-1.2 -1-0.5 m 2.75 m 5.4 m 5.4 m 5.6 m 5.6 0 0.7 0 1.3 o 1.3 o 1.5 o 1.5 22-28 55-110 40-90 70-175 70-130 33-42 60-85 50-65 60-90 55-90 (m 75) (m 80) 0.6-1.0 1.0-1.2 0.8-1.0 1.1-1.3 1.0-1.3 1.8-2.1 1.3-1.8 1.6-1.9 1.5-1.9 1.5-2.0 (m 2.0) (m 1.6) (m 1.8) (m 1.7) (m 1.8) 1.5-1.8 0.5-1.2 1.1-1.5 0.5-1.3 0.6-1.2 0.4-0.78 -1-0.3 0.9-6.2 0.6-1.2 1.4-9.0 1.0-8.0 D. E. Lawson / 15 frame). Most of the sediments have attained stability and are being revegetated. Further, measurements of active layer thickness suggest that a thermal equilibrium is being established in accordance with the modified physical con- ditions. Hence, it appears unlikely that the sites’ terrain configuration and thermal regime will return in the near future, if ever, to their original conditions prior to dis- turbance. The observations do suggest that the Oumalik basin site might have been restored more closely to its undisturbed state if it had been leveled to the original grade when it was abandoned. The time frame within which physical stability de- velops, and subsequently a new thermal regime is estab- lished, is difficult to ascertain. The nature of the degra- dational processes, the observed extent of physical changes, and the continuing activity of degradational pro- cesses at some locations (notably East Oumalik) indicate that the relative lengths of time over which particular DISCUSSION AND The contrast between the 30-yr-old former drill sites, where length and seasons of occupation and types of activities causing disturbance were similar, indicates that the resulting types of degradational processes and their relative importance differed, and that this difference is directly related to the properties of the perennially frozen sediments and terrain. Ice content, dimensions, and dis- tribution of ice wedges and other types of massive ground ice, geotechnical properties of the sediments immediately after thawing, and effective relief within and around the site are the primary factors determining this relationship. Within a particular site, the type of disturbance further determines the severity of impact. The most extensive modifications occurred on each site at those locations dis- turbed by removal of the vegetative mat and soil. At East Oumalik, thawing of the ice-rich silt at these locations produced sediment with little or no strength that was highly susceptible to failure and mechanical erosion. Natural relief on the site, combined with local increases in relief as thaw subsidence took place, were sufficient to cause failure of thawing slopes by gravitational pro- cesses and cause meltwater erosion of interconnected thaw depressions. Degradation subsided only after thaw bulb expansion was minimized by reduced availability of melt- water, increased sedimentation in thaw depressions, and changes in slope angle. By comparison, the thawed sands at Fish Creek resisted mechanical erosion and were not highly susceptible to failure, given the natural relief of the site and only minor modifications in relief that resulted from thaw subsi- dence. The small volume of ground ice and small size of ice wedges strictly limited the physical changes that took place. At Oumalik, the ridge contained thaw-unstable silts, larger ice wedges, and a well-developed drainage system that led to thermal and mechanical erosion mainly along 16 / ARcTIC AND ALPINE RESEARCH degradational processes were active, and hence the length of time before relatively stable physical conditions were attained, differed from site to site. Further, the rates of physical change differed at each site depending upon the types and relative importance of degradational processes that were initiated by disturb- ance. Most changes at Fish Creek and the Oumalik basin resulted from thaw subsidence and consolidation, while at East Oumalik, thaw subsidence was accompanied by a variety of erosional and slope processes that extended and prolonged site modifications. Hence, the East Oumalik site probably took at least 10 to 15 yr before a significant diminishment in the degradational processes could be seen, whereas the Fish Creek upland or the drained lake basin at Oumalik probably slowed rapidly in modification and exhibited little physical change after five years or so. CONCLUSIONS gullies that terminated at the base of the ridge slope. Lateral expansion of degradation was less extensive than at East Oumalik because of the lower ice content of the silt between the ice wedges. The poorly drained basin had fewer physical changes, and these were similar in style to the ones at the Fish Creek site because of the smaller size of the ice wedges and its naturally wet state. Any lateral movements in thawed materials occurred under oversaturated conditions, perhaps subaqueously, thus rapidly lowering slope angles as thaw subsidence took place. The standing water may also have damped the thermal effects of the disturbance as well. The time necessary to attain a physical stability suffi- cient to permit vegetation to establish itself varied with the extent and type of degradation. Within five years or so, locations where vegetation had been removed at Fish Creek and the wet Oumalik basin were probably being revegetated, whereas 15 or more years may have been re- quired before revegetation began at East Oumalik and bare areas still remained at East Oumalik in 1982. Once vegetation is established, root growth and increased cover assist in stabilizing surficial materials. Contrasts between the three sites indicate that the sus- ceptibility of areas underlain by perennially frozen ground to physical modifications as the result of a disturbance may be defined by detailed analysis of certain physical properties of the materials in the frozen and thawed state. The volume, distribution, and dimensions of massive ground ice are particularly important parameters. In addi- tion, an analysis of sediment properties including the tex- ture, void ratio, density, water content, degree of satura- tion, and liquid limit can determine whether they are thaw-stable or unstable, and thus their potential suscep- tibility to erosional and gravitational processes of degra- dation that lead to long-term and extensive impacts after the thermal regime is disturbed. Further, natural relief of a site combined with changes in elevation and slope as thaw subsidence takes place after the initial disturb- ance, particularly in areas of massive ground ice, deter- mine drainage and affect the type and extent of degra- dational processes that act upon the thawed sediment. A combined mapping of major landforms, ice volume, mas- sive ground ice distribution, and surficial material types may prove useful for deriving maps of perennially frozen terrain’s susceptibility to long-term modifications by dif- ferent types of disturbance. ACKNOWLEDGMENTS This work was funded at CRREL by the U.S. Geological Survey under its National Petroleum Reserve-Alaska Program. I thank Bruce Brockett for working with me in the field on the sampling program, and Max Brewer, George Gryc, and Jerry Brown for encouraging and fully supporting this research. I also thank Jerry Brown, Kaye Everett, Larry Johnson, David Murray, Skip Walker, Pat Webber, Jim Ebersole, and Gus Shaver for discussions of this research and their critical review of an earlier version of this manuscript, and Art Lachenbruch and Sam Outcalt for critically reviewing this manuscript for pub- lication. REFERENCES CITED Abele, G., Brown, J., and Brewer, M. C., 1984: Long-term effects of off-road vehicle traffic on tundra terrain. Journal of Terramechanics, 21: 283-294. Bliss, L. C., 1970: Oil and ecology of the Arctic. 7-ransactions, Royal Society of Canada, 4th Series, VII: 1-12. Brockett, B. and Lawson, D. E., 1985: Prototype drill for core sampling fine-grained perennially frozen ground. Hanover, NH: U.S. Army Cold Regions Research and Engineering Lab- oratory, CRREL Report, 85-1. 29 pp. Haugen, R. K. and Brown, J., 1980: Coastal-inland distribu- tions of summer air temperature and precipitation in north- ern Alaska. Arctic and Alpine Research, 12: 403-412. Lawson, D. E., 1979: Human-induced thermokarst processes at East Oumalik, northern Alaska. Geological Society of America Annual Meeting, San Diego, Abstracts with Pro- gram, 11: 463. , 1982: Long-term modifications of perennially frozen sediments and terrain at East Oumalik, northern Alaska. Hanover, NH: U.S. Army, Cold Regions Research and Engi- neering Laboratory, CRREL Report, 82-36. 30 pp. , 1983: Ground ice in perennially frozen sediments, northern Alaska. Jn: Permafrost: Fourth International Con- ference, Proceedings. Washington, D.C.: National Academy Press, 695-700. Lawson, D. E. and Brockett, B., 1980: Drilling and coring of frozen ground in northern Alaska, spring 1979. U.S. Army Cold Regions Research and Engineering Laboratory, CRREL Special Report, 80-12. 14 pp. Lawson, D. E., Brown, J., Everett, K. R., Johnson, A. W., Komarkova, V., Murray, B. M., Murray, D. M., and Webber, P. J., 1978: Tundra disturbances and recovery following the 1949 exploratory drilling, Fish Creek, northern Alaska. U.S. Army Cold Regions Research and Engineering Laboratory, CRREL Report, 78-28. 112 pp. Lawson, D. E. and Brown, J., 1979: Human-induced thermo- karst at old drill sites in northern Alaska. The Northern Engi- neer, 10(2): 16-23. Mackay, J. R., 1970: Disturbances to the tundra and forest tundra environment of the western Arctic. Canadian Geo- technical Journal, 7: 420-432. Reed, J. C., 1958: Exploration of Naval Petroleum Reserve No. 4 and adjacent areas, northern Alaska. U.S. Geological Sur- vey Professional Paper, 301. 192 pp. Ms submitted May 1985 D. E. Lawson / 17