Ninth International Conference on Permafrost ... - IARC Research

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A Hypothesis: A Condition of Growth of Thick Ice WedgesAnatoli BrouchkovTyumen State Oil and Gas UniversitySo-called Ice Complex or “edoma” in Siberia, whichrepresents extremely ice-rich and perennially-frozensediments with thick polygonal ice wedges, is formed interritories acting as terrestrial accumulation basins duringthe Pleistocene. It sometimes consists of more than 90% iceby volume. Simplifying, a decrease of temperature causessoil to shrink and cracks to form; then water seeps into thecracks in spring. It freezes and expands when it is chilledby permafrost. This cycle continues to enlarge the wedgesyear by year until the soil above the wedges is pushed upand finally almost disappears around. However, details ofthe mechanism of thermal contraction cracking and icewedge formation still remain unclear (French 1996). Ice isknown to be able to flow under loads, and it probably couldbe easier for ice to be pressed up than for soil. Why do weobserve the result of soil pushing up only, not ice, and whatis the mechanical condition of the process?Water freezing and expanding when it is chilled bypermafrost can be expressed by the Clapeyron equation.Stresses can be estimated approximately as 13.4 MPa pera decrease in negative temperature by 1°C. In the case ofmechanical equilibrium, if horizontal stresses σ zare equalin soil and ice, the heaving strain of about 9% of volumeof freezing water ε fis connected to mechanical compressionof frozen soil (dσ z*l fr/Е fr) and ice (dσ z*l ice/Е ice), being of l frand l icein size and having the strain modulus Е frand Е ice,respectively:dεf(1)dσz=lfr lice+E EfriceIf, for example, ε fis 0.0045 m as a result of freezing of0.05 m of water, l fr= 5 m and l ice= 0.5 m, and the long-tempcompression modulus Е fr= 20 MPa and Е ice= 50 MPa, thenstress σ z= 0.017 MPa. In many cases, the value of ε fis evenless then 0.05 m; for example 0.001–0.003 m only in Barrow(Black 1951), and 0.002–0.01 m in Kolyma plain (Berman1965). Due to higher modulus values, compression of soilreaches 4.33 and ice 0.17 mm consequently. The size of thedeformed soil area varies, for example, near Fairbanks in therange of 0.3–3 m (Pewe 1962). The lateral strains dependingon Poisson’s ratio will be less than compression, but probablythey will be more for soil than for ice. Stresses are small andperhaps unable to make considerable structural changes ofsoil mass. Repeating a thousand times, it results in ice wedgethickness of about 4 m. This is generally in agreement withthe point that soil is pushed up during ice wedge formation.However, it was found that soil layers at a certain distancefrom the ice wedge are almost not affected (Popov 1965).An area of high density of deformed soil should be createdon contact with an ice wedge to give space to ice, and thatarea should be gradually increased in size in accordance withan increase of wedge thickness. One reason for the deformedarea to remain small is the stress distribution in soil mass.The stresses are basically not equal and become smallerwith distance from an ice wedge. Using q/unit length on thesurface of a semi infinite soil mass, or if the excess stressis according to the Boussinesq equation (Ahlvin & Smoots1988), the stress can be found approximately:σ∆ σ ~ I(2)zz n zwhere n changes from about 1 to 2, I = influence factor forthe load, and z = distance from the ice wedge. Formula (1)should be adjusted then according (2). If horizontal stress σ z= 0.017 MPa near an ice wedge, it is about σ z= 0.004 MPaonly on distance of 2 m. Thus, stresses might be too smallto cause deformations far from the ice wedge, but they arebig enough to move soil particles and pore ice near the icewedge. Another reason for the deformed area to be small isperhaps because of gradual movement of attached ice soiltowards the surface together with ice caused by pressure andbuoyancy.Signs of diapirism and soil circulation are widespread inperiglacial areas (Hallet & Waddington 1991). Buoyancy canbe an effective driving force in the case of ice wedges dueto different densities of frozen soil (1.5–1.7 and more cm 3 /g)and ice (0.9–1 cm 3 /g). If the size of polygons are more thanor equal to the height of an ice wedge h, and the viscosity ofice η iis much less than the viscosity of the surrounding soilη s, the rate of vertical movement of an ice wedge wall υ willbe (Artyushkov 1969):2ρ ghυ ~ ∆ (3)ηswhere ∆ρ = difference of densities of soil and ice; g = gravityacceleration, 9.81 m/sec; η s= viscosity of surrounding soil,Pa*s. However, the assumption that the viscosity of ice isless than the viscosity of the surrounding soil is far frombeing acceptable: relationship is opposite. The ice viscositycan be assumed as 10 12 –10 13 Pa*s, and frozen soil viscosityas 10 10 –10 11 Pa*s. The buoyancy of an ice wedge and itsvertical movement z can still be found from the similarNavier-Stoks equation:2∆ρglv ~~ tz18η s(4)where t = time; l = width of ice wedge. If the width of the icewedge l = 1 m, and time t is 1000 years, then resurfacing ofice can reach about 1.5 m. That value of vertical movementmay change the shape of ice wedges drastically, especially insaline or high-temperature permafrost. Vertical orientation of33
Ni n t h In t e r n at i o n a l Co n f e r e n c e o n Pe r m a f r o s trod-shaped air bubbles (Kurdyakov 1965), “echelon breaks”(Pewe 1962), and the foliated structure of ice can serve asindirect evidence of it. Sometimes soil layers near an icewedge look like they are “drawing in ice” (Pewe 1962).Flexures of soil layers near ice wedges are mostly directed up(Popov 1965) probably because of vertical ice flow. Unusualdeformations of soil layers under an ice wedge, describedby Kostyaev (1965) in the Yana River terrace, can also be aresult of buoyancy. Ice wedges flowing upward 1–3 m, likediapers, were described by Black (1983).Therefore, the thick ice wedges can be formed easier inconditions of low values of the soil creep threshold σ 0and theirhigher deformability; it is a condition of their growth by thecracking-fullfiling-freezing mechanism. Stresses induced byfreezing are small and perhaps unable to make considerablestructural changes of soil mass. However, creep thresholdσ 0values of frozen saline soil are low, and that gives a vitalreason for wide distribution of thick ice wedges in regionsof saline permafrost. Ice is able to flow at any stress, andshould be flowing up during ice wedge formation. A numberof features appears to be created during the evolution of icewedge shape due to the flow; among them irregular shapesof underground ice are common. Buoyancy can be anothereffective driving force in the case of ice wedges due to thedifference of densities of frozen soil and ice. An estimationshows the buoyancy of ice can reach substantial values.Kostyaev, A.G. 1965. Ice wedges and convective instabilityof soils. In: Underground Ice, Issue 1. For the 7th<strong>International</strong> Congress on Quarternary (INQUA),USA. Moscow University Press, 133-140 (inRussian).Kurdyakov, V.S. 1965. Polygonal ice-wedges in Amguemariver basin. In: Underground Ice, Issue 1. For the 7th<strong>International</strong> Congress on Quarternary (INQUA),USA. Moscow University Press, 87-103 (inRussian).Pewe, T.L. 1962. Ice wedges in permafrost, Lower Yukonriver near Galena Alaska. Biuletyn Peryglacjalny 11.Lodz.Pewe, T.L. 1966. Ice wedges in Alaska: Classification,distribution and climatic significance. Proceedingsof the First <strong>International</strong> <strong>Conference</strong> on Permafrost.National Academy of Science: National ResearchCouncil of Canada, Publication 1287, 76-81.Popov, A.I. 1965. Underground ice. In: UndergroundIce, Issue 1. For the 7th <strong>International</strong> Congress onQuarternary (INQUA), USA. Moscow UniversityPress, 7-39 (in Russian).ReferencesAhlvin, R.G. & Smoots, A.V. 1988. Construction Guidefor Soils and Foundation. New York: John Wiley &Sons.Artyushkov, E.V. 1969. About pressing of ice-wedges bysurrounded deposits. In: Problems of Cryolithology,Issue 1. Moscow University Press, 34-37 (inRussian).Berman, L.L. 1965. Underground ice in northern part ofKolyma plain. In: Underground Ice, Issue 1. Forthe 7th <strong>International</strong> Congress on Quarternary(INQUA), USA. Moscow University Press, 112-119(in Russian).Black, R.F. 1951. Structure in ice wedges of NorthernAlaska. Geol. Soc. Am. Bull. 62, Pt. 2.Black, R.F. 1983. Three superposed systems of ice wedges atMcLeod Point, northern Alaska, may span most of theWisconsian stage and Holocene. Proceedings of theFourth <strong>International</strong> <strong>Conference</strong> on Permafrost, July17–22, 1983. Washington, DC: National AcademyPress, 68-73.French, H.M. 1996. The Periglacial Environment, 2nd ed.Longman, Harlow, 1-341.Hallet, B. & Waddington, E.D. 1991. Buoyancy forces inducedby freeze-thaw in the active layer: Implications fordiapirism and soil circulation. In: J.C. Dixon & A.D.Abrahams (eds.), Periglacial Geomorphology. JohnWiley and Sons Ltd., 251-279.34
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NICOP 2008 Ninth <
Page 6 and 7: ContentsPreface ...................
Page 8 and 9: Mapping and Modeling the Distributi
Page 10 and 11: Satellite Observations of Frozen Gr
Page 13 and 14: xiiIce Wedge Thermal Regime in Nort
Page 15 and 16: xivPermafrost Response to Dynamics
Page 17 and 18: xvi
Page 19 and 20: NICOP SponsorsUniversitiesUniversit
Page 22 and 23: Deep Permafrost Studies at the Lupi
Page 24 and 25: Effect of Fire on Pond Dynamics in
Page 26 and 27: Cryological Status of Russian Soils
Page 28 and 29: Acoustical Surveys of Methane Plume
Page 30 and 31: Permafrost Delineation Near Fairban
Page 32 and 33: Preparatory Work for a Permanent Ge
Page 34 and 35: A Provisional Soil Map of the Trans
Page 36 and 37: Martian Permafrost Depths from Orbi
Page 38 and 39: Time Series Analyses of Active Micr
Page 40 and 41: Impact of Permafrost Degradation on
Page 42 and 43: DC Resistivity Soundings Across a P
Page 44 and 45: Modeling Thermal and Moisture Regim
Page 46 and 47: A Provisional Permafrost Map of the
Page 48 and 49: Alpine Permafrost Distribution at M
Page 50 and 51: Cryogenic Formations of the Caucasu
Page 52 and 53: Modeling Potential Climatic Change
Page 56 and 57: Modeled Continual Surface Water Sto
Page 58 and 59: Freeze/Thaw Properties of Tundra So
Page 60 and 61: Discontinuous Permafrost Distributi
Page 62 and 63: Thermal Regime Within an Arctic Was
Page 64 and 65: Seasonal and Interannual Variabilit
Page 66 and 67: Twelve-Year Thaw Progression Data f
Page 68 and 69: Continued Permafrost Warming in Nor
Page 70 and 71: Landsliding Following Forest Fire o
Page 72 and 73: A Permafrost Model Incorporating Dy
Page 74 and 75: Seasonal Sources of Soil Respiratio
Page 76 and 77: Greenland Permafrost Temperature Si
Page 78 and 79: The Importance of Snow Cover Evolut
Page 80 and 81: The Account of Long-Term Air Temper
Page 82 and 83: The Combined Isotopic Analysis of L
Page 84 and 85: Adaptating and Managing Nunavik’s
Page 86 and 87: Human Experience of Cryospheric Cha
Page 88 and 89: HiRISE Observations of Fractured Mo
Page 90 and 91: A Soil Freeze-Thaw Model Through th
Page 92 and 93: Mapping and Modeling the Distributi
Page 94 and 95: First Results of Ground Surface Tem
Page 96 and 97: Historical Changes in the Seasonall
Page 98 and 99: Rock Glaciers in the Kåfjord Area,
Page 100 and 101: Snowpack Evolution on Permafrost, N
Page 102 and 103: Climate Change in Permafrost Region
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Maximizing Construction Season in a
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Pleistocene Sand-Wedge, Composite-W
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370Huang, B. 339Hugelius, G. 105, 1
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