Wildfires in Arctic regions impact landforms via permafrost degradation and subsequent deformation that can last for many years. However, it remains uncertain on if and how much deformations occur, and what controls their magnitude, particularly during the first couple of years. Here, we examine the transient post-fire deformation responses near the Batagaika megaslump, which is the world's largest retrogressive thaw slump at Batagay, Sakha Republic. There were wildfires in the summers of 2018 and 2019 on the same slope, which could trigger the formation of another megaslump; many fires occurred nearby in 2019. We use interferometric synthetic aperture radar (InSAR) to measure surface displacements, including both post-fire and span-fire images. We also perform onsite measurements of temperature and thaw depth around the two scars near Batagaika megaslump in 2019, 2020, and 2021 and around the 2014 scar in 2019. At the three fire scars formed in 2018 and 2019, we demonstrate year-to-year and location-specific changes in the amplitude of subsidence, heave, and duration. The 2018 scar shows cumulative subsidences of up to 10 cm by March 2021, more clearly than the nearby 2019 scar. On the other hand, another 2019 scar adjacent to the 2014 scar shows up to 13 cm net subsidence during the first span-fire year, although the subsiding area is limited. These diverse transient post-fire responses demonstrate that under the yedoma area the spatial heterogeneities of the active layer depth and the timing of fires will control subsequent thermokarst processes.

A characteristic of frozen ground is a tendency to form banded sequences of particle-free ice lenses separated by layers of ice-infiltrated soil, which produce frost heave. In permafrost, the deformation of the ground surface caused by segregated ice harms engineering facilities and has considerable influences on regional hydrology, ecology, and climate changes. For predicting the impacts of permafrost degradation under global warming and segregated ice transformation on engineering and environmental, establishing appropriate mathematical models to describe water migration and ice behavior in frozen soil is necessary. This requires an essential understanding of water migration and segregated ice formation in frozen ground. This article reviewed mechanisms of water migration and ice formation in frozen soils and their model construction and introduced the effects of segregated ice on the permafrost environment included landforms, regional hydrological patterns, and ecosystems. Currently, the soil water potential has been widely accepted to characterize the energy state of liquid water, to further study the direction and water flux of water moisture migration. Models aimed to describe the dynamics of ice formation have successfully predicted the macroscopic processes of segregated ice, such as the rigid ice model and segregation potential model, which has been widely used and further developed. However, some difficulties to describe their theoretical basis of microscope physics still need further study. Besides, how to describe the ice lens in the landscape models is another interesting challenge that helps to understand the interaction between soil ice segregation and the permafrost environment. In the final of this review, some concerns overlooked by current research have been summarized which should be the central focus in future study.

Freeze-thaw cycles (FTC) are known to have an effect on railway track stability, safety, and performance. FTC are expected to become more frequent in the future due to climate change. This paper presents the results of a field investigation in which the mechanism of FTC development within the track embankment and its effect on the performance of railway tracks including track surface deformation and track geometry degradation are studied. Field observations suggested that the frost depth within the track embankment is influenced by the freezing index and winter snow cover. They also showed that a warmer and drier winter leads to more intermittent FTC and even though the average frost heave is lower than for a colder winter, the frost heaves occurring at culvert locations creates a larger differential deformation and thus may lead to a worse operating condition. The comparison of geometry measurements before freezing and after thawing indicated that the track geometry is in poorer and rougher condition during springs that were preceded by increased FTC. It was also concluded that track in proximity to culverts suffered the highest geometry degradation. Overall, the limited field observations of this study suggest that future winters, mild with less precipitation and higher occurrence of FTC, may increase the rate of track deterioration and more maintenance will be required to keep track within safe limits.

Nordenskiold Land in Central Spitsbergen, Svalbard is characterized as a high latitude, high relief periglacial landscape with permafrost occurring both in mountains and lowlands. Freezing and thawing of the active layer causes seasonal frost heave and thaw subsidence, while permafrost-related mass-wasting processes induce downslope ground displacements on valley sides. Displacement rate varies spatially and temporally depending on environmental factors. In our study, we apply Satellite Synthetic Aperture Radar Interferometry (InSAR) to investigate the magnitude, spatial distribution and timing of seasonal ground displacements in and around Adventdalen using TerraSAR-X StripMap Mode (2009-2017) and Sentinel-1 Interferometric Wide Swath Mode (2015-2017) SAR images. First, we show that InSAR results from both sensors highlight consistent patterns and provide a comprehensive overview of the distribution of displacement rates. Secondly, two-dimensional (2D) TerraSAR-X InSAR results from combined ascending and descending geometries document the spatial variability of the vertical and east-west horizontal displacement rates for an average of nine thawing seasons. The remote sensing results are compared to a simplified geomorphological map enabling the identification of specific magnitudes and orientations of displacements for 14 selected geomorphological units. Finally, June to December 2017 6-day sampling interval Sentinel-1 time series was retrieved and compared to active layer ground temperatures from two boreholes. The timing of the subsidence and heave detected by InSAR matches the thawing and freeze-back periods measured by in-situ sensors. Our results highlight the value of InSAR to obtain landscape scale knowledge about the seasonal dynamics of complex periglacial environments.

Needle ice growth is one of the more widespread and easily visible, but less studied, climate related processes shaping soil evolution, surface dynamics and ecosystem changes in the alpine environments. Here, we show the results of the monitoring of needle ice development at four plots located at 2670 m a.s.l. close to the Stelvio Pass in the Italian Central Alps during 2016. Needle Ice formation and evolution with time was monitored through the photogrammetric technique of the Structure from Motion (SfM). Our monitoring data included also quantitative measurements of some selected physical and climatic parameters like air temperature, ground temperature and ground water content at depths of 2 and 5 cm. Our data demonstrate that needle ice can develop with a relatively low ground water content (13.2%), at a relatively high minimum ground temperature (-0.3 degrees C) and with a low cooling rate (< 1.8 degrees C h(-1)). Moreover, for the first time, we observed that needle ice can form below a thin snow cover (< 25 mm) that can enhance the sensible heat flow from the ground to the atmosphere and, therefore, promote the cooling of the near surface ground. Statistically, the minimum air temperature results in the leading factor for the needle ice growth. The total frost heave seems to be related to the abundance of fine material (although we couldn't demonstrate it statistically). The absence of statistically significant relationships between frost heave and frost creep could be probably due to the importance of the observed needle ice toppling and the possible sliding of the clasts during the melting phases.

Nonsorted circles and earth hummocks are important landscape components of the arctic tundra. Here we describe the vegetation on these frost-heave features at seven study sites along a N-S-transect from the Arctic Ocean to the Arctic Foothills, Alaska. We established 117 releves in frost-heave features and surrounding tundra and classified the vegetation according to the Braun-Blanquet sorted-table method. We used Detrended Correspondence Analysis to analyze relationships between vegetation and environmental variables. We identified nine communities: Braya purpurascens-Puccinellia angustata community (dry nonsorted circles, subzone C); Dryas integrifolia-Salix arctica community (dry tundra, subzone C); Salici rotundifoliae-Caricetum aquatilis ass. nov. (moist coastal tundra, subzone C); Junco biglumis-Dryadetum integrifoliae ass. nov. (moist nonsorted circles, subzone D); Dryado integrifoliae-Caricetum bigelowii Walker et al. 1994 (moist tundra, subzone D); Scorpidium scorpioides-Carex aquatilis community (wet tundra, subzone D); Cladino-Vaccinietum vitis-idaeae ass. nov. (dry nonsorted circles and earth hummocks, subzone E); Sphagno-Erlophoretum vaginati Walker et al. 1994 (moist tundra, subzone E); and Anthelia juratzkana-Juncus biglumis community (wet nonsorted circles, subzone E). The DCA ordination displayed the vegetation types with respect to complex environmental gradients. The first axis of the ordination corresponds to a bioclimate/pH gradient, and the second axis corresponds to a disturbance/soil moisture gradient. Frost-heave features are dominated by lichens, whereas the adjacent tundra supports more dwarf shrubs, graminoids and mosses. Frost-heave features have greater thaw depths, more bare ground, thinner organic horizons and lower soil moisture than the surrounding tundra. The morphology of frost-heave features changes along the climatic gradient, with large, barren nonsorted circles dominating the northern sites and vegetated, less active earth hummocks dotting the southern sites. Thawing of permafrost and a possible shift in plant community composition due to global warming could lead to a decline in frost-heave features and result in the loss of landscape heterogeneity.

Recent Canadian research on permafrost is reviewed, concentrating on permafrost-climate relations, the processes of thermokarst, ice-wedge development, frost heave and soil convection, and ground ice studies. This field of geomorphology is often of direct interest to engineers and managers of northern resource development. While industrial activity in the Arctic is currently slow, concern for the effects of permafrost stability of global climate warming has stimulated research. Much of the work on the potential consequences to permafrost of climate change is by modelling: there are yet few relevant field data, although this is crucial for model evaluation. Studies of permafrost processes usually rely on geotechnical or geophysical theory too: the review concentrates on the use of field evidence in support of analytical models of landform development. Current research on ground ice is of a more geological nature: we examine approaches to the delineation and origin of massive ice.