CHANGES IN PERMAFROST CONDITIONS ALONG LINEAR ENGINEERING STRUCTURES IN THE NORTH-TAIGA SUBZONE OF THE ARCTIC AREA,

E.G. Karpov, E.L. Baranovsky

Igarka Permafrost Investigation Station, Melnikov Permafrost Institute, SB RAS, Igarka 663200, Territory, Russia e-mail: [email protected]

Abstract

Multi-year studies, carried out along linear engineering structures in the north-taiga subzone of the arctic Yenisey area, have revealed the following:

(1) contemporary degradation of permafrost due to clearing of forest tracts and disturbance of moss and lichen cover;

(2) steady-state permafrost with a tendency towards increases in temperature due to climate warming during the last decade;

(3) contemporary aggradation of permafrost on top of mineral frost mounds due to thinner and more com- pacted snow cover along linear engineering structures;

(4) degradation of permafrost along the abandoned Igarka-Sukharikha railway due to damming of surface water derived from rain and snowmelt, with resultant development of bogs and of thermokarst processes; for- mation of permafrost below the railway bed.

New data (9 years of observations) are presented on the change in thermal regime of an open talik beneath partially-drained Shchuchie Lake located at the Arctic Circle.

Introduction The most complicated and vulnerable part of the route extends for 130 km from the Gutkocha River to During the period 1989-1997, changes in geocryologi- the Kholpakov River (90 km south and 40 km north of cal conditions along a linear route extending for 388 km Igarka) and has a thick cover of unconsolidated from the Kureika hydropower station to were Quaternary sediments with very complicated geocry- studied in relation to disturbances involved with con- ological conditions. struction and operation/maintenance conditions. Disturbances included clearing of forest vegetation, Based on nine years of field observations on the recent partial destruction of sod cover by crawler-type vehi- state and dynamics of permafrost in this vulnerable cles in summer, drying-out of moss and lichen cover part of the line, the route can be divided into two types and its subsequent replacement by grasses, and the pre- of permafrost: (1) unstable, degrading, and (2) stable, dominant regeneration of birch and larch. The route with a tendency to aggradation. consists of two parallel lines constructed at different times: the older one in 1974-1977, the younger one in Unstable, degrading permafrost 1985-1989. Each line is 50 m wide. GEOCRYOLOGICAL PROFILE 1 Parts of the studied route from the Kureika River up Geocryological profile 1 is situated 80 km south of the to the Gutkocha River and from the Kholpakov River to city of Igarka, in the Sukharikha-Kureika interfluve at Norilsk are characterized by shallow bedrock overlain elevations up to 100 m. This profile, consisting of four by a thin cover of rocky, loose sediments. These parts drillholes (31-34), was made on the left bank of the are less problematic and more favorable for reliable Bolshiye Kozharki River in a tract of north-taiga, mixed, operation of the line VL-220 kWt. thin, mossy, spruce-birch-larch forest with a thick (10-15 cm) moss and lichen cover. In this area, the older line route was cleared in 1979 and is now overgrown

E.G. Karpov, E.L. Baranovsky 545 with a young birch forest (very thick in places). The -0.1¡C at a depth of 5.5 m. Hole 44 which was drilled trees are 2-4 m (rarely up to 5-6 m) high and are 2-6 cm 20 m away from hole 44a at an edge of a thermokarst in diameter. The younger line route was cleared in the depression penetrated through an open talik with a summer of 1985 and is not overgrown with a forest yet. temperature 0.6¡C at a depth of 7 m. Holes 32 and 33, sunk on the younger and older routes respectively, and hole 31, drilled in a forest some 50 m Thus, forest clearing has led to tremendous changes in from the newer line route, exposed poorly frozen, ice- geocryological conditions, causing complete degrada- poor, predominantly massive-structured bouldery till tion of the permafrost along these two line routes du- (suglinok) that grades into a bouldery gravel at a depth ring the last 15-20 years. Changes in geocryological con- of 6 m. Hole 34, sunk in forest in the rear part of the ditions gave rise to changes in the surface conditions, Bolshiye Kozharki River valley, 100 m away from the leading to the development of young thermokarst older line route, exposed ice-saturated, lenticular- depressions and hillocky terrain with flat basins as a braided-structured, typical ribbon clays of glacio- result of thawing of previously ice-saturated lacustrine origin underlain by bouldery pebbles. In all Quaternary sediments. drillholes, the upper part of the ground section is made up of 2-3 m thick, rusty brown-grey till with rare boul- GEOCRYOLOGICAL PROFILE 3 ders. As on-site observations indicate, the forest (holes Geocryological profile 3 is situated 25 km north of 31 and 34) has permafrost with a temperature of Ð0.2¡C Igarka, 1 km away from the Yenisey River, on a forested (as of May 18, 1991), whereas in the cleared areas, only 50 m high hill crosscut by creek valleys and 5-10 m short-term permafrost has remained to a depth of 3.5- deep basins of thermokarst lakes. Hole 73a, sunk in a 4.0 m. The thickness of the active layer is 1.2-1.5 m in forest, 30 m away from the newer line route, reached forested areas and increases up to 2.5 m in the cleared permafrost at a depth of 1 m that had a temperature of areas. Over the observation period, the snow cover -0.2¡C at a depth of 7 m. Holes, drilled on the axes of varied in height from 80-90 cm in cleared areas up to the routes and at a border with the forest, exposed the 160-180 cm in forest, i.e., half as much in open places permafrost table, unfrozen in its upper part, at different due to blowing away by strong blizzards. The snow depths. Along profile 3, the depth of such a degraded thickness of 80-90 cm has proven to be sufficient to pre- permafrost layer was 3.5 m at the older route-forest bor- vent the soils of the open areas from strong freezing. der (hole 71), 4.5 m on the axis of the older route (hole Cutting-down of the forest and disturbance of the moss 72), and 5.5 m on the axis of the newer one (hole 73). cover causes unidirectional, fast thawing and degrada- tion of the permafrost along power line routes. Thus, a thick unfrozen layer (up to 3.5-5.5 m) above the permafrost table, the gradient-free character of soil GEOCRYOLOGICAL PROFILE 2 temperatures in the cleared areas, and descent of the Geocryological profile 2 permits us to make judg- upper boundary of frozen sediment are all indicative of ments about the character of changes in geocryolitho- degrading permafrost in this area as a result of cutting- logical conditions in relation to partial cutting of the down of forest vegetation and disturbance of moss and forest (prior to the construction of the line routes). This lichen covers (drying-out, disappearance and replace- profile passes 750 m northeast from the outskirts of the ment by grasses). older part of the city of Igarka in a hilly watershed dip- ping toward a boggy depression. The city of Igarka is SUPPORTING STRUCTURE 267 surrounded by a secondary, mixed, predominantly In early October (the end of maximum thawing sea- spruce-birch forest with a lot of old stumps remaining son) of 1995, we found along the newer line route, a from 1929, the time of development of this territory. faulty supporting structure (267) that was constructed Holes were sunk in a forest along the axes of the two in 1985. This support is located 2 km northeast of the line routes. In this place, the older and newer routes are Taiga settlement (not far from Igarka). Here, the terrain 50 m apart. For comparison, two more holes were sunk is a gently undulating, boggy, hummocky surface of an in a glade. old glacio-lacustrine plain with elevations up to 49-57 m. The support is mounted on four separate, Holes 43 and 45, sunk on the line routes, exposed 3.7 m long reinforced concrete piles with 2.4 m wide open taliks with temperatures, respectively, of 0.9¡C square shoes at the base. Paired piles with shoes are and 0.7¡C at a depth of 7 m. Hole 43a, drilled 40 m west mounted on 3.0 m by 1.8 m-sized concrete slabs. The of the older route in a forest, atop a residual mound, support stands in a marginal part of an oblong mineral exposed ice-saturated permafrost with a temperature frost mound that is 3-4 m high, 8-12 m to 30-50 m in -0.2¡C at a depth of 7 m. Hole 44a, sunk on a small, width and more than 250 m long. residual mineral mound (2 m in height and 15 m in diameter) in a glade between the two routes, also The pile foundations of the support rest on frozen, ice- exposed ice-saturated permafrost with temperature of saturated clays of glacio-lacustrine origin. The clays

546 The 7th International Permafrost Conference have lenticular-braided cryogenic structure (typical of Profile 4, made in March of 1991, passes from the the Igarka area) and gravimetric moisture contents of creek thalweg to the top of the frost mound. The soils of 115-263 %. Some lenses of segregated ice are 5-10 cm to the frost mound are in a stable, perennially frozen state 15 cm thick. Permafrost may be at least 10-15 m thick at and have a temperature of -0.3¡C at the depth of zero this location. The active layer depth on the frost mound annual fluctuations. The upper part of the soil is made with a sparse grassy cover reaches 1.7-2.0 m. Hole 86, up of ice-poor, massive-structured, dark brown till sunk 18 m north of hole 85 at the bottom of a 2 m deep (suglinok) containing plant remains. It grades down- draining depression, exposed very wet open taliks with ward, at 1.7 m to 5 m depth, into ice-rich, bluish-grey ground temperatures of +1¡C at 3-5 m depth. ribbon clays with thick interlayers of segregated ground ice. At a 5-7 m depth, the ice content of the clays Forest clearing and partial damming of the drainage decreases sharply and the cryogenic structure becomes of the depression have caused renewal of contemporary massive. The depth of the active layer on the mound themokarst and thermal erosion processes. Intensive reaches 2 m and snow cover height is 0.1-0.4 m. development of ground subsidence and cave-in At the foot of the mound and in the bed of the creek, processes on steep slopes of the frost mound is evi- there are taliks underlain warm frozen ground at a denced by large subsidence fissures in the near-surface depth of 6-7 m. The snow cover height at this location is and sliding of soil towards the surrounding bogs and 160-180 cm. depression. Subsidence fissures at the slope edges are up to 0.5 m deep, 0.2-0.3 m wide and a few dozen In the area around the support where the soil was meters long. replaced by fill (boulder-pebble mixture with a silty filler), the ground is also perennially frozen; the active A leveling survey, carried out on April 12, 1996, layer depth is 2.0-2.2 m and the snow cover height revealed differential settlement and deformation of is 40-50 cm. piles 1, 2, 3 of support 267 in comparison with the least settled pile 4. Pile 1, which is adjacent to the draining The support failure was caused by heave at the foun- depression, settled by 301 mm, whereas piles 2 and 3 dation as a result of growth of the frost mound and had moved 73 mm and 17 mm, respectively. Some set- build-up of permafrost at the base where it contacts tlement of pile 4 cannot be excluded as it is also with the underlying talik, as well as by lateral water deformed, although less so than the other three piles. feed from a pseudo-talik. Up to 0.6 m deep and 0.2 m wide radial fissures at the surface (sod and soil) on the Thus, failure of support 267 was caused by rapid slopes and top of the frost mound serve as irrefutable thermokarst activity and thermal erosion processes as a evidence of the growth of the mound. result of a rise in ground temperature at the pile bases and thawing of ice-saturated soils below the support Based on our observations, the following conclusion foundation due to the lateral and downward warming can be reached concerning the character of the heave effect of a dammed water mass with a depth of 2 m and that led to the support failure: temperatures up to 20-25¡C. 1. It was the result of areal, slow (13-year) growth of Stable permafrost with a tendency the mineral frost mound in height (thickening and more to aggradation severe conditions of the permafrost with decreasing temperature) due to changes in the surface conditions GEOCRYOLOGICAL PROFILE 4 (cutting-down of forest vegetation, decrease in snow Geocryological profile 4 is situated in the older line cover height around the support). In such circum- route, 300 m north of the Igarka railway substation, stances, slow aggradation of permafrost occurs at the near faulty support 283, on the surface of an old glacio- base as a result of water attracted to the freezing front lacustrine where ribbon clays with relatively thin, from the surrounding and underlying unfrozen ground, warm, ice-saturated, discontinuous, sometimes island, under open system conditions. permafrost occurs. 2. One cannot exclude (excessive) increase in the Support 283 stands atop a small mineral frost mound water content of boulder-pebble soils below the support with an elevation of 4.5 m above the level of a swampy or shoes and subsequent freezing to form injected thalweg of Bezimyanny Creek. Its failure happened 13 ground ice lenses. years after its construction as a result of intense heave and build-up of the frost mound at the contact with the GEOCRYOLOGICAL PROFILE 5 underlying unfrozen ground. The metal support This profile is situated 200 m southeast of the cracked 2-3 m above the foundation and fell down. Taimenye lake, on the surface of a forested morainal ridge with absolute elevations of 67 m (water level in

E.G. Karpov, E.L. Baranovsky 547 Table 1. Change in temperature (C) of an open talik at 5-10 m depth below the dry bed of Shchuchye Lake (in 20 drillholes) over 9 years of observations subsequent to its draining in August of 1988

the lake is 30 m). Here, the terrain is rugged, hilly, of There is no change in ground temperature of -0.3 to glacio-lacustrine origin, dipping slightly towards the -0.4¡C at 6 m depth along the profile, although strong lake, with mixed forest dominated by spruce and downward freezing of soils is observed within the first Siberian larch. Soils consist of boulder-rich till (push 3-4 m. The strongest freezing of soils is noted along moraine), with fragmentary material increasing both line routes in the area of holes 40, 41 where the towards the bottom of 4 to 6 m deep holes. From ground temperatures at 3 m depth are cooler by 1-2¡C. drilling data, the larger part of the profile (in areas of In undisturbed forest, the permafrost is practically gra- holes 39, 40, 41) is made up of permafrost (massive- dient-free across the section. Hole 40, drilled on the axis textured bouldery till with low ice content) with tem- of the older route in a small (20 m by 30 m) sedge bog, peratures of -0.3 to -0.4¡C at 6 m depth. Unfrozen suggests that an open talik existed at this location prior ground with a 0.5 m thick seasonally freezing layer was to forest cutting. As is shown by temperature measure- exposed only in hole 42 sunk in an undisturbed forest ments, the talik has frozen during the last 17 years and area, on the right side of the newer line route. the ground temperature at 6 m depth is -0.2 to -0.3¡C. Observations from 1993 show the following snow cover distribution dynamics: 140-150 cm in forest; 60-70 cm Our observations indicate that open, elevated areas of along the older route; 90-100 cm along the newer route. the line routes are characterized by half as much thick-

548 The 7th International Permafrost Conference Table 2. Thermal dynamics (C) of unfrozen ground below the dried part of the bed of Shchuchye Lake (hole 38)

nesses of the snow cover due to blowing-out and com- ding of the terrain along the railway, development of a paction of the snow and more severe permafrost specific hydrothermal regime and cryogenic processes conditions. dominated by thermokarst settlement.

Change in geocryological conditions along Freezing of an open talik below an abandoned railway a drained lake

Our study of the abandoned, incomplete railway Formation of a contemporary permafrost under natur- (1948-1953) began in 1994 with a transverse geocryolog- al conditions has been studied since 1989 in the basin of ical profile of four drillholes that was made in a fores- a partially drained Shchuchye Lake of thermokarst ori- ted watershed in the area of the Chernaya River, 15 km gin. The lake is located near a thermokarst of the south of Igarka. Holes 76a and 76b (the former on top of Ledyanaya Gora outcrop, close to the Arctic Circle, on a 1.5 m high embankment and the latter at its foot) the right bank of Yenisey, 130 km south of Igarka (along exposed permafrost, respectively, at a depth of 1 m and the river channel). Draining of the approximately 5 m 1.5 m, having temperatures of -0.4¡C and - 0.1¡C at deep lake took place on August 18, 1988 in relation to depths of 3 m and 3.5 m. Hole 76, which was sunk close natural dynamics of development of the Ledyanaya to a draining depression, did not encounter permafrost Gora thermokarst. The dried part of the lake basin and the ground at 3 m depth had a temperature became overgrown by grass in the first summer; in sub- of +0.2C. sequent years it became covered with thick grassy vege- tation (mainly cereals and sedge). At present, the bot- For comparison, a 4.5 m deep hole, 77, was drilled in a tom of the lake is overgrown with thick purple willows natural forest with 0.15-0.2 m thick moss and lichen and birch trees. In April of 1989 and June of 1990, six cover, 100 m east of the embankment. Here, soils are geocryological profiles were made at various places in frozen, ice-saturated and have a temperature of -0.8¡C the drained part of the lake basin. Each profile consists (as of 7th July 1994). Depth of maximum seasonal tha- of 2 to 6 holes with a depth of 5 to 10 m (profile 1: holes wing at the end of September was 1 m. Frozen, red, 30-32; profile 2: holes 38, 41, 37, 42-44; profile 3: holes Igarka-type sandstone, lies at a depth of 5 m below the 39, 47, 48, 52; profile 4: holes 49-51; profile 5: holes 45, surface. The rough surface of the bedrock was also 46; profile 6: holes 40, 53; see Table 1). exposed in holes 76a and 76b at 3-4 m depth. From drilling data, the lake-bottom sediments (up to The above data indicate that significant changes 10 m depth) are made up of homogeneous, redeposited, occurred in the geocryological conditions along the compacted till (suglinok) and clay, sometimes with abandoned Igarka-Sukharikha railway, with complete peaty sediments in the upper part; all holes exposed an degradation of permafrost as a result of a 50 m wide aquifer (diluted silt) at depths below 6 m. The moisture clear cut and damming of melt and rain water by an content of the sediments from the surface to 6 m depth embankment, resulting in the formation of bogs, floo- varied from 20-40 % by weight. The temperature of the

E.G. Karpov, E.L. Baranovsky 549 unfrozen ground at 5 to 10 m depth remains practically Formation of permafrost on the former lake bed can unchanged, varying, depending on the distance to the be restrained by accumulation of a thick, friable snow water edge and on the basin depth (bottom relief, from cover amidst willows and birch trees (2 m and more 0.9¡C to 4.2¡C (mostly up to 3.3¡C), see Table 1). Table 1 high) that may prevent fast freezing of the talik. gives total temperature change in the open talik below the lake over nine years of observations. In all of the 20 Conclusions drillholes, a decrease in the temperature of unfrozen ground of 0.7¡C to 1.4¡C is observed. The results of our study of changes in geocryological conditions along linear engineering structures in the Table 2 presents data on the thermal dynamics of Igarka region can be summarized as follows: unfrozen ground below a dried bottom of the Shchuchye Lake obtained in hole 38 sunk near the for- 1. Intensive development of contemporary mer water edge. As can be seen from the Table 2, on thermokarst and thermal erosion processes (permafrost June 29, 1989, at 10-m, the hole exposed an open talik degradation) leads to failure of supporting structures. with a temperature of +0.9¡C. During subsequent years, the temperature of the talik at 10 m depth decreased 2. Contemporary aggradation of the permafrost gradually to 0.0C (as of June 3, 1997). In the winter of occurs in mineral frost mounds due to thinner and 1989-90, the talik froze to a depth of 2.5 m to form a more compacted snow cover in open (deforested) areas more that 1 m thick layer of short-term permafrost. In of the line route. subsequent years, the permafrost gradually grew in thickness up to 3-4 m and reached 5 m in 1997, but the 3. Complete degradation of permafrost is found along ground temperature at 5-10 m depth remains at 0.0¡C. an abandoned railway due to formation of bogs as a result of damming of melt water by the railway Thus, for a nine-year period, all 20 holes show not embankment. Below the embankment, island per- only a general decrease in the temperature of the mafrost is formed. unfrozen ground, but also a steady formation of up to 5 m thick of contemporary permafrost beneath the 4. Newly-formed contemporary permafrost and a slopes of a drained lake basin with maximum active decrease in temperature of an open talik was measured layer depth of 1.2 m at the end of September. The thick- in the partially drained bed of Shchuchye Lake. ness of a newly-formed permafrost in hole 38 is 3.8 m. One can expect slow formation of contemporary per- 5. The most stable and relatively "severe" permafrost mafrost in the drained part of the bottom of the is observed on unforested hillocky peatlands where Shchuchye Lake and advance, from the former shore- contemporary frost fissures with epigenetic wedge ice line, of the low-temperature (-1.9¡C at 10 m depth), are developed. thick (approximately 190 m), ice-saturated permafrost that surrounds the talik below the lake.

550 The 7th International Permafrost Conference