Soil Thermal Conditions Research Articles

The effectiveness of low-grade geothermal heat usage under the conditions of the Russian climate

This paper reports the results of a study of the effectiveness of using low-grade ground heat for heat pump systems in the climatic conditions throughout Russia. The study was performed using the software package “INSOLAR.GSHP.12”, which simulates the non-stationary thermal conditions of ground source heat pumps (GSHPs) over several years of operation. The impact of long-duration ground heat collection on soil thermal conditions and the impact of phase transitions of ground moisture on the effectiveness of GSHP operation were taken into consideration during the simulation.The GSHP energy conversion factor (COP, the ratio of useable thermal energy produced by the GSHP to the energy expended to operate the GSHP) average for the 5th year of operation was used as a criterion of to make efficiency zones of Russia. The results of the zonation study are maps of the territory of Russia with contours reflecting the coefficients of energy conversion and unit cost of energy consumption for GSHP operation with vertical and horizontal systems for the collection of low-grade geothermal heat and assigned to 1m2 of heated area of a building.

Environmental drivers of cambial phenology in Great Basin bristlecone pine.

The timing of wood formation is crucial to determine how environmental factors affect tree growth. The long-lived bristlecone pine (Pinus longaeva D. K. Bailey) is a foundation treeline species in the Great Basin of North America reaching stem ages of about 5000 years. We investigated stem cambial phenology and radial size variability to quantify the relative influence of environmental variables on bristlecone pine growth. Repeated cellular measurements and half-hourly dendrometer records were obtained during 2013 and 2014 for two high-elevation stands included in the Nevada Climate-ecohydrological Assessment Network. Daily time series of stem radial variations showed rehydration and expansion starting in late April-early May, prior to the onset of wood formation at breast height. Formation of new xylem started in June and lasted until mid-September. There were no differences in phenological timing between the two stands, or in the air and soil temperature thresholds for the onset of xylogenesis. A multiple logistic regression model highlighted a separate effect of air and soil temperature on xylogenesis, the relevance of which was modulated by the interaction with vapor pressure and soil water content. While air temperature plays a key role in cambial resumption after winter dormancy, soil thermal conditions coupled with snowpack dynamics also influence the onset of wood formation by regulating plant-soil water exchanges. Our results help build a physiological understanding of climate-growth relationships in P. longaeva, the importance of which for dendroclimatic reconstructions can hardly be overstated. In addition, environmental drivers of xylogenesis at the treeline ecotone, by controlling the growth of dominant species, ultimately determine ecosystem responses to climatic change.

Simulating the thermal operating conditions in the thermal wells of ground-source heat-pump heat supply systems. Part II: Consideration of porous moisture phase transitions in soil

The mathematical model describing unsteady thermal operating conditions of ground-source heat-pump (GSHP) heat supply systems that takes into account porous moisture condensation/evaporation processes and that is laid down in the basis of the corresponding block of the INSOLAR.GSHP.12 software system is considered. The results of numerical and laboratory experiments confirming that the GSHP performance efficiency depends essentially on the phase transition processes of moisture contained in the soil strata porous space are presented. The problem of correctly taking into account the heat of porous moisture condensation/evaporation phenomena in simulating the thermal processes occurring in the soil strata surrounding GSHP thermal wells is considered. A mathematical description of porous moisture condensation/evaporation processes for a vertical thermal well in the cylindrical coordinate system is given. A numerical experiment on estimating the effect the porous moisture condensation/evaporation processes have on the soil thermal conditions was carried out after the mathematical model had been implemented in a software block. The presented results obtained from the performed numerical experiment show that the temperature levels of soil adjacent to the thermal well determined with and without taking the heat of porous moisture condensation processes may differ from each other by more than 3°C. The results from experimentally approbating the application of a so-called effective soil thermal conductivity coefficient that takes into account the latent heat of porous moisture phase transitions in soil in modeling the GSHP thermal operating conditions are presented. The results of the performed experiments show that porous moisture phase transitions may have a very significant influence on the effective thermal conductivity of soil. The effective thermal conductivity values of soil may differ from each other by several times depending on the soil system operating conditions.

Simulating the thermal operating conditions in the thermal wells of ground-source heat-pump heat supply systems. Part I: Porous moisture freezing processes in soil

The mathematical models laid down in the new blocks of the INSOLAR.GSHP.12 software system simulating unsteady operating conditions of ground-source heat-pump (GSHP) heat supply systems are presented. The new model blocks take into account the effect the freezing of porous moisture in soil has on the GSHP system performance efficiency. Illustration is given to the need of taking into account the porous moisture freezing/thawing processes in soil, and the results from investigations devoted to the opening possibilities of constructing adaptive GSHP systems with controlled intensity of heat transfer in the soil-thermal well system are presented. The development of software simulating the porous moisture phase state variation processes in soil was preceded by development of mathematical equations representing the thermal conditions of soil body involving porous moisture freezing/thawing processes. A description of these equations is also given in the article. In constructing the mathematical model, the notion “effective thermal conductivity” of soil was introduced for taking into account the latent heat of phase transition that releases during the freezing of moisture. The above-mentioned effective thermal conductivity of soil involves two components: the soil thermal conductivity coefficient itself and an additional term modifying the thermal conductivity value for taking into account the influence of phase transition. For quantitatively evaluating the soil effective thermal conductivity component that takes into account the influence of phase transition, the soil freezing zone radius around the thermal well was determined. The obtained analytic solutions have been implemented in the form of computer program blocks, after which a “numerical experiment” was carried out for estimating the effect the porous moisture freezing/thawing processes have on the soil thermal conditions. It was demonstrated during that experiment that the soil thermal conductivities determined without taking the porous moisture freezing/thawing phase transitions can differ from those determined with taking these transitions into account by a factor of 2 or more. A conclusion has been drawn from these findings about the importance of taking the phase transition phenomena into account in modeling the parameters of thermal wells and of the GSHP system as a whole.

Specifics of Mathematical Simulation and the Method of Modeling for Subway Tunnels Thermal Conditions

This paper contains the results of research, carried out with financial support from the Ministry of Education and Science of the Russian Federation and dedicated to improving the energy efficiency of Moscow subway facilities and creation of stations with "zero" external sources heat consumption. The paper presents a method of simulation of the thermal conditions for subway tunnels, which allows, overcoming the difficulties associated with the informative uncertainty of baseline data, as well as difficulties associated with the approximation of the external parameters. Advantage of this method is the fact that the usage of so-called "base" experimentally obtained information about the natural soil thermal conditions in this model, can partially take into account the whole range of factors, which have significant influence on the formation of the thermal regime of the tunnel but are almost impossible to be taken into account within the strict formulation of the problem today.

Intermittent experimental study of a vertical ground source heat pump system

In this paper, the intermittent experiment of a vertical ground source heat pump (GSHP) system is investigated and the corresponding geo-temperature variations are studied. The performance of the GSHP system under intermittent operation and the comparisons of different intermittent modes are presented in the paper. The parameters of soil backfill material, air temperature and inlet volume flow rate are also investigated. Experimental results suggest that, due to the recovery in ground thermal energy in intermittent time, the heat exchange rate and the operation performance coefficient (COP) of the heat pump increases, and the compressor power decreases in the successive working. But an insufficient soil recovery time leads to a rapid decline of the performance parameters and the soil temperature. The temperature transports faster under large soil thermal conductivity conditions and the soil temperature decreases more quickly and recovers more slowly with larger inlet flow rate and lower weather temperature for different soil thermal diffusivities. Through multiple nonlinear regression analysis, a curve formula can be fitted to predict the soil temperature variations under intermittent operation of the ground source heat pump in winter, Dalian. It can be found that the soil temperature increases at an exponential function with each factor.

The Influence of Subway’s Underground Facilities Operation on the Natural Thermal Conditions of Adjacent Soil

This paper contains the results of research dedicated to improving the energy efficiency of Moscow subway facilities and creation of stations with "zero" external sources heat consumption. The paper presents a method of simulation of the thermal conditions for subway tunnels, which allows overcoming the difficulties associated with the informative uncertainty of baseline data, as well as difficulties associated with the approximation of the external parameters, affecting the soil's thermal conditions. Advantage of this method in comparison with the traditional approach to the modeling of thermal processes in such systems is the fact that the usage of so-called "base" experimentally obtained information about the natural soil thermal conditions in this model, can partially take into account the whole range of factors (such as presence of the groundwater, it's speed and thermal conditions, the structure and location of the soil layers, the "thermal" background from the Earth, precipitation, phase transformation of moisture in the pore space, and more), which have significant influence on the formation of the thermal regime of the tunnel but are almost impossible to be taken into account within the strict formulation of the problem today. The method has been implemented in the software package INSOLAR.GSHP.12, created by JSC "INSOLAR-INVEST".

Comparison of ecosystem characteristics between degraded and intact alpine meadow in the Qinghai-Tibetan Plateau, China

Climate warming and overgrazing are inducing degradation of the alpine meadow ecosystem on the Qinghai-Tibetan Plateau. The Plateau is an important pastoral region in China and controversy surrounds the estimated carbon release occurring in this region of the world. Nevertheless, little comprehensive research analyzing land degradation has been conducted involving multiple factors in this region. Using two years of observational data, we compared differences in air temperature and relative humidity, soil temperature and moisture, soil texture, soil bulk density, soil organic carbon, soil respiration, vegetation height, coverage and biodiversity, above- and below ground biomass between moderately degraded and intact alpine meadow, and analyzed their relationships. The results show that the main process occurring during degradation was that Spenceria species and weeds with deep roots and a relatively high ability to resist drought replaced Kobresia species that previously exhibited high vegetation coverage and low vegetation height in alpine meadows of the Qinghai-Tibetan Plateau; these changes fundamentally affected corresponding changes in soil physical, chemical and thermal characteristics of the meadows. The change of vegetation species is believed to be the result of drought in the shallow soil of this habitat and is controlled by temperature and precipitation. The results suggest that a good collocation between temperature and precipitation is beneficial to the development of the alpine meadows; conversely, a poor pairing of temperature and precipitation not only causes the degradation of alpine meadows, it can even continually intensify the process by creating a vicious circle involving changes in soil physical, chemical, thermal and hydraulic conditions.

Creation of an artificial frozen barrier using hybrid thermosyphons

Standard containment technologies for remediation of subsurface contaminants include slurry walls, reactive barriers, sheet piling, and grouting. Another less common technique is freezing contaminants in situ. Artificial freezing techniques can be used to create a frozen barrier that restricts migration of aqueous phase contaminants and, therefore, can provide subsurface containment at a variety of facilities, including underground tanks, nuclear waste sites, groundwater plumes, and in situ waste treatment areas. Frozen barriers are formed by using a series of subsurface freezing pipes. The adjacent soil forms a frozen column the length of the freezing pipe; and the diameter of the frozen soil column increases with time at a rate depending upon the specific soil properties, moisture content, and thermal conditions at a given site and refrigeration rate (i.e., pipe temperature). The barrier is completed once the increasing diameters of the frozen soil columns merge together, which is referred to as “freezing to closure”. A study was performed in Fairbanks, Alaska, to investigate how quickly a barrier can be created during the summer using actively cooled hybrid thermosyphons. Freezing to closure occurred after 42days, the barrier was 1m thick after approximately 49days, and temperatures were below −3°C at the core of the barrier (in between the thermosyphons) after 60days. The active system was turned off in the fall, and passive cooling of the ground continued through the winter. By the beginning of the following March, the frozen barrier was 3.8m thick.

Reconciling soil thermal and hydrological lower boundary conditions in land surface models

The lower boundary condition of soil in land surface models is a key parameter, which can affect the energy and water budget at the surface/atmosphere interface. Indeed, it affects the thermal inertia of the ground as well as the water fluxes from the subsurface to the river‐aquifer system. In land surface models, it is well known that the soil must be sufficiently deep to compute a realistic soil temperature profile, while in terms of hydrology, the soil column should be substantially thinner in order to simulate realistic river discharges and therefore surface fluxes. In addition to the confirmation of this paradox, the goal of this study is to show how it is solved in the Interaction between Soil Biosphere Atmosphere (ISBA) land surface model. To reconcile hydrological and thermal lower boundary conditions, a simple approach is developed in which the soil temperature profile is extended below the hydrological column of the soil, and the water profile is extrapolated at each thermal node as the depth increases. ISBA is applied across France over 20 years and at a relatively high resolution. Additional experiments are also performed using the same lower boundary conditions of 1, 2, 3, 5, and 12 m for hydrological and thermal equations. The simulated river discharges and temperature profiles are compared to a dense network of in situ observations. The results confirm the paradox addressed previously and demonstrate that, if left unsolved, it could lead to poor simulation of the soil water and energy budgets, potentially affecting the performance of forecast studies, hydrological applications, and/or climate modeling.

On parameterization of heat conduction in coupled soil water and heat flow modelling

Soil water and heat transport plays an important role in various hydrologic, agricultural, and industrial applications. Accordingly, an increasing attention is paid to relevant simulation models. In the present study, soil thermal conditions at a mountain meadow during the vegetation season were simulated. A dual-continuum model of coupled water and heat transport was employed to account for preferential flow effects. Data collected at an experimental site in the Šumava Mountains, southern Bohemia, during the vegetation season 2009 were employed. Soil hydraulic properties (retention curve and hydraulic conductivity) determined by independent soil tests were used. Unavailable hydraulic parameters were adjusted to obtain satisfactory hydraulic model performance. Soil thermal properties were estimated based on values found in literature without further optimization. Three different approaches were used to approximate the soil thermal conductivity function, λ(θ): (i) relationships provided by Chung and Horton (ii) linear estimates as described by Loukili, Woodbury and Snelgrove, (iii) methodology proposed by Côté and Konrad. The simulated thermal conditions were compared to those observed. The impact of different soil thermal conductivity approximations on the heat transport simulation results was analysed. The differences between the simulation results in terms of the soil temperature were small. Regarding the surface soil heat flux, these differences became substantial. More realistic simulations were obtained using λ(θ) estimates based on the soil texture and composition. The differences between these two, related to neglecting vs. considering λ(θ) non-linearity, were found negligible.

The spatial variation of alpine timberlines and their biogeographical characteristics in the northern Tianshan Mountains of China

Alpine timberline is a proper indicator of climate change and has received much attention in ecological research during the past decades. In this study, variations of alpine timberlines and their biogeographic characteristics were investigated by a combination of field surveys, climate indices, and soil nutrient analyses in the northern Tianshan Mountains (NTM) of northwest China. The timberline altitudes were probed to range from 2,530 to 2,800 m a.s.l. in the NTM, gradually descending from west to east along the V-shaped Ili valley (from Zhaosu to Xinyuan), and ascending from west to east across the northernmost range of the study area (from Bole to Balikun). The vertical widths between the upper and lower limits of the timberlines were widest in the middle NTM (Kuytun to Changji) and the Ili valley (Zhaosu to Xinyuan). Interactions between the terrain and air currents resulted in variant climates within the NTM, which contributed to significant timberline distribution differences. Although vertical width was positively correlated to soil nutrient (especially organic matter, r = 0.78), and timberline altitudes were positively related to the soil pH values, the temperature during the growing season primarily determines both altitude and vertical width. In conclusion, timberline altitudes were dominated by the combined effects of local topography, soil nutrient properties, water, and thermal conditions. Identifying the dominating influencing factors of NTM timberlines provided potential insights to better understand the effects of climate change on the alpine ecosystem over central Asia.

Boreal and subarctic soils under climatic change

Changing climate and warming atmosphere are supposed to result in changing thermal regimes of soils with a spectrum of impacts for terrestrial heat-flow, ecological and biochemical processes including vegetation and carbon dynamics. Here, six sites within an area of significant recent climatic warming, between 70° and 60°N, provided data of air and soil temperatures and snow depth to analyze the spatiotemporal air–soil temperature associations during the period 1971–2010. The air temperatures exhibited significant trends of warming across the boreal and subarctic regions. The records of snow depth showed trends of snowpack thinning and the soil temperature trends of warming especially in the southern and middle boreal sites. The boreal and subarctic sites showed predominant influence of air temperature variability on soil thermal conditions, with modulating effects of thermoinsulation caused by the snowpack. The yearly variations in soil temperatures correlated highly with those of air temperatures and the positive trend in soil temperatures was sufficiently explained by air temperature warming in the majority of the sites. The results thus propose that the climate change could be directly causing alterations in the soil thermal regime and the warming of soils, with generally expected continuation, driven by air temperature warming as projected by model simulations. The thermoinsulation effects during the winter were strongest in the northern boreal zone where the temperature difference between the air and soil temperatures was largest and the correlations between snow depth and soil temperatures were highest during the winter months. Likewise, the rate of air temperature warming appeared strongest in our northern boreal site where the soil temperature warming showed non-significant trend only. The evidence for temporal air–soil temperature decouplings and spatial disparity between the air and soil temperature data both expressed the importance of studying the soil temperature change in situ. In the same context, the potential for temperature induced soil organic carbon decomposition coincided spatially with the highest quantities of available carbon as indicated for our boreal and subarctic soils.

Predicting Soil Moisture and Temperature of Andisols under a Monsoon Climate in Japan

Predicting the effects of climate change on the vadose zone is a new and important application of the analysis of simultaneous heat and water movement between the atmosphere and the vadose zone. The HYDRUS‐1D software system, with meteorological submodels that evaluate the surface water and energy balance, has been reported to be a useful tool for predicting field thermal and moisture conditions in semiarid regions. Application of the physical model to a humid climate and all types of soils is necessary because this climate has pronounced biological activity and thus significantly contributes to the global environment. The purpose of this study was to evaluate the usefulness of HYDRUS in predicting annual changes in soil moisture and temperature in the vadose zone under a monsoon climate. The model was evaluated using observed data from a western suburb of Tokyo. The soil properties utilized in the simulation were obtained using laboratory experiments. Climate data for the meteorological submodels were obtained from open‐access climate records. The observed surface heat flux agreed well with the predicted surface heat flux produced by the meteorological submodels. The numerical results produced by HYDRUS using the meteorological submodels represented annual changes in soil thermal and moisture conditions fairly well. Our results show that the meteorological submodels of HYDRUS are appropriate to produce thermal and water boundary conditions under a monsoon climate. This suggests that HYDRUS has the potential to simulate the physical conditions of the vadose zone by using forecast climate data coupled with global circulation models.

Influence of litter layer removal on the soil thermal regime of a pine forest in a mediterranean climate

The removal of the litter layer in Portuguese pine forests would reduce fire hazard, but on the other hand this practice would influence the thermal regime of the soil, hence affecting soil biological activity, litter decomposition and nutrient dynamics. Temperature profiles of a sandy soil (Haplic Podzol) under a pine forest were measured with thermocouples at depths to 16 cm, with and without litter layer. The litter layer acted as a thermal insulator, reducing the amplitude of the periodic temperature variation in the mineral soil underneath and increasing damping depths, particularly at low soil water contents. At the mineral soil surface the reduction of amplitudes was about 2.5 ºC in the annual cycle and 5 to 6.7 ºC in the daily cycle, depending on the soil water content. When soil was both cold and wet, mean daily soil temperatures were higher (about 1 - 1.5 ºC) under the litter layer. Improved soil thermal conditions under the litter layer recommend its retention as a forest management practice to follow in general.

Growth and development of maize ( Zea mays L.) in response to different field water management practices: Resource capture and use efficiency

Soil–water supply is the main factor limiting crop production across the Loess Plateau in China. A two-year field experiment was conducted to evaluate three possible water management practices – film mulching (FM), supplementary irrigation (SI) and rain-fed (RF, control) – in terms of resource capture and use efficiency in maize ( Zea mays L.) in this area. The cumulative intercepted photosynthetically active radiation (PAR i), air thermal time (TT air), soil thermal time (TT soil) and evapotranspiration (ET) were monitored during both crop growing seasons, and the effects of the three treatments on the growth dynamics and grain yield (GY) of the maize crops were compared. The results showed that the FM treatment significantly accelerated development of the crop plants, and the SI treatment induced more rapid development in the vegetative stage than the RF treatment. Both FM and SI treatments markedly increased the shoot dry matter (DM) and GY ( p < 0.05). The cumulative PAR i, TT air and TT soil during the reproductive stage were all significantly increased by both the FM and SI treatments relative to the RF treatment ( p < 0.05), correlating well with observed increases in DM and GY. Both the FM and SI treatments also resulted in significantly higher ( p < 0.05) radiation use efficiency, and the FM treatment significantly increased the water use efficiency, by 23–25%, in both years ( p < 0.05). The results show that the tested water management practices have significant effects on soil moisture and thermal conditions, and hence the rates of growth and development of maize, in fields on the Loess Plateau, China.

A Hydrothermal Seedling Emergence Model for Giant Ragweed (Ambrosia trifida)

Late-season giant ragweed emergence in Ohio crop fields complicates decisions concerning the optimum time to implement control measures. Our objectives were to develop a hydrothermal time emergence model for a late-emerging biotype and validate the model in a variety of locations and burial environments. To develop the model, giant ragweed seedlings were counted and removed weekly each growing season from 2000 to 2003 in a fallow field located in west central Ohio. Weather data, soil characteristics and geographic location were used to predict soil thermal and moisture conditions with the Soil Temperature and Moisture Model (STM2). Hydrothermal time (θHT) initiated March 1 and base values were extrapolated from the literature (Tb= 2 C, ψb= −10 MPa). Cumulative percent emergence initially increased rapidly and reached 60% of maximum by late April (approximately 400 θHT), leveled off for a period in May, and increased again at a lower rate before concluding in late July (approximately 2,300 θHT). The period in May when few seedlings emerged was not subject to soil temperatures or water potentials less than the θHTbase values. The biphasic pattern of emergence was modeled with two successive Weibull models that were validated in 2005 in a tilled and a no-tillage environment and in 2006 at a separate location in a no-tillage environment. Root-mean-square values for comparing actual and model predicted cumulative emergence values ranged from 8.0 to 9.5%, indicating a high degree of accuracy. This experiment demonstrated an approach to emergence modeling that can be used to forecast emergence on a local basis according to weed biotype and easily obtainable soil and weather data.

Hydrothermal pattern of frozen soil in Nam Co lake basin, the Tibetan Plateau

Hydrothermal processes and the regimes of frozen soil formed in alpine regions with glaciers and lake area are complex and important for ecological environment but have not been studied in Tibet. Based on soil temperature and moisture data from October 2005 to September 2006 collected in the Nam Co lake basin, Tibetan Plateau (TP), those questions were discussed. The mean annual air temperature was −3.4°C with 8 months below 0°C. Air and soil temperature varied between −25.3~13.1°C and −10.3~8.8°C, respectively. Soil moisture variations in the active layer were small with the minimum value of 1.4%, but were influenced greatly by snowmelt, rainfall and evaporation, varying up to 53.8%. The active layer froze later, thawed earlier and was thinner, however, the lower altitude limit of permafrost is higher than that in most areas of TP. The effects of soil moisture (unfrozen water content) on soil temperature, which were estimated through proposed models, were more significant near ground surface than the other layers. The surface soil temperature decreased with snowcover, the effect of cold snow meltwater infiltration on soil thermal conditions was negligible, however, the effect of rainfall infiltration was evident causing thermal disruptions.

Fluxes and production of N2O, CO2 and CH4 in boreal agricultural soil during winter as affected by snow cover

Agricultural soils are important source of atmospheric nitrous oxide (N2O) and a considerable part of annual N2O release occurs during the cold season in the boreal region. According to recent studies N2O can be produced in soils at low temperatures, below 0°C. We studied if removal of the snowcover lowers soil temperatures and whether this would affect flux rates of N2O, carbon dioxide (CO2) and methane (CH4) from an agricultural soil in eastern Finland. Gas flux rates and concentrations in soil were measured from study plots with undisturbed snow cover and from plots with snow removed. This experiment simulates changes in the soil thermal conditions with less snowfall. Plots without snow had even 15°C lower temperature at the depth of 5 cm and they had higher N2O emissions during soil freezing and thawing. However, there were only minor changes in CH4 or CO2 flux rates after removal of snow over the cold season. N2O and CO2 accumulated in the soil during winter and were then released rapidly during thawing in spring. CH4 concentrations in the soil remained lower than the atmospheric levels during winter and subsequently increased to the ambient levels after thawing. Future climate scenarios suggest possible decline in snowfall in northern Europe resulting in lower soil temperatures. This could lead to higher N2O emissions from boreal agricultural soils.

Movement, moisture and thermal conditions at a turf‐banked solifluction lobe, Kluane Range, Yukon Territory, Canada

AbstractA turf‐banked solifluction lobe was instrumented for the continuous recording of surface and internal movement, thaw settlement, soil volumetric moisture content and thermal conditions during the spring and summer of 2002. Strain probe measurements showed that gelifluction occurred as a series of discrete and abrupt displacements near the thaw plane, followed by retrograde movement. Most gelifluction events took place when thaw rates were high and the soil was saturated almost to the surface, but rain was also capable of inducing gelifluction at depth. The rapid and localized character of the observed displacements suggests that gelifluction results from micro‐shearing of the soil, possibly along the interface of thawing ice lenses. Copyright © 2005 John Wiley &amp; Sons, Ltd.