Top-of-permafrost ground ice indicated by remotely sensed late-season subsidence

Ground ice is foundational to the integrity of Arctic ecosystems and infrastructure. However, we lack fine-scale ground ice maps across almost the entire Arctic, chiefly because there is no established method for mapping ice-rich permafrost from space. Here, we assess whether remotely sensed late-season subsidence can be used to identify ice-rich permafrost. The idea is that, towards the end of an exceptionally warm summer, the thaw front can penetrate materials that were previously perennially frozen, triggering increased subsidence if they are ice rich. Focusing on northwestern Alaska, we test the idea by comparing the Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) late-season subsidence observations to permafrost cores and an independently derived ground ice classification. We find that the late-season subsidence in an exceptionally warm summer was 4–8 cm (5th–95th percentiles) in the ice-rich areas, while it was low in ice-poor areas (−1 to 2 cm; 5th–95th percentiles). The distributions of the late-season subsidence overlapped by 2 %, demonstrating high sensitivity and specificity for identifying top-of-permafrost excess ground ice. The strengths of late-season subsidence include the ease of automation and its applicability to areas that lack conspicuous manifestations of ground ice, as often occurs on hillslopes. One limitation is that it is not sensitive to excess ground ice below the thaw front and thus the total ice content. Late-season subsidence can enhance the automated mapping of permafrost ground ice, complementing existing (predominantly non-automated) approaches based on largely indirect associations with vegetation and periglacial landforms. Thanks to its suitability for mapping ice-rich permafrost, satellite-observed late-season subsidence can make a vital contribution to anticipating terrain instability in the Arctic and sustainably stewarding its ecosystems.

Carrying load of column poles of railway bridges that are designed according the I-st principle on permafrost ground

The paper presents results of development of a method for determination of carrying load of column poles of railway bridges that are based on permafrost ground and designed according the I-st principle. It also shows the necessity to use methods of mathematical modeling for determination of thermal mode of permafrost ground in the foundation of artificial constructions, which will allow forecasting the carrying load of bridge poles for any term of operation. As a result, the paper shows an algorithm for calculation and forecasting of carrying load of bridge poles at degradation of permafrost in their foundation.

Vulnerable top-of-permafrost ground ice indicated by remotely sensed late-season subsidence

Ground ice is foundational to the integrity of Arctic ecosystems and infrastructure. However, we lack fine-scale ground ice maps across almost the entire Arctic, chiefly because ground ice cannot be observed directly from space. Focusing on northwestern Alaska, we assess the suitability of late-season subsidence from Sentinel-1 satellite observations as a direct indicator of vulnerable excess ground ice at the top of permafrost. The idea is that, towards the end of an exceptionally warm summer, the thaw front can penetrate materials that were previously perennially frozen, triggering increased subsidence if they are ice rich. For locations independently determined to be ice rich, the late-season subsidence in an exceptionally warm summer was 4–8 cm (5th–95th percentile), while it was lower for ice-poor areas (−1–2 cm). The distributions overlapped by 2 %, demonstrating high sensitivity and specificity for identifying top-of-permafrost excess ground ice. The strengths of late-season subsidence include the ease of automation and its applicability to areas that lack conspicuous manifestations of ground ice, as often occurs on hillslopes. One limitation is that it is not sensitive to excess ground ice below the thaw front and thus the total ice content. Late-season subsidence can enhance the automated mapping of vulnerable permafrost ground ice, complementing existing (predominantly non-automated) approaches based on largely indirect associations with vegetation cover and periglacial landforms. Improved ground ice maps will prove indispensable for anticipating terrain instability in the Arctic and sustainably stewarding its ecosystems.

Active rock glaciers as shallow groundwater reservoirs, Austrian Alps

Rock glaciers are the most prominent landforms of alpine permafrost and comprise complex shallow aquifer systems in (high) alpine catchments. Recession analyses of groundwater discharge of four active rock glaciers that contain permafrost ground ice show that they have a base flow component of the order of a few liters per second, similar to that of a relict rock glacier in which permafrost ground ice is absent. This is related to an unfrozen (fine-grained) base layer with a thickness of about 10 m. Based on a threshold analysis of precipitation events and event water discharge, depressions atop the bedrock or the permafrost table seem to play only a minor role in storing groundwater. This important finding has rarely been documented, but is highly relevant for optimal groundwater resources management in sensitive (high) alpine catchments and ecosystems. All the rock glaciers analyzed here are located in the Austrian Alps and represent the nationwide sites where suitable discharge data are available. The analysis highlights the hydrogeological importance of these discrete permafrost-derived debris accumulations as complex shallow groundwater bodies with important—but limited—storage and buffer capabilities.

Оptimization of thermal stabilization of soils applications

To provide the first principle of usage the permafrost ground as the base it is necessary to design methods that eliminate or decrease structures thermal influence on permafrost.Usually choosing thermal stabilization solutions the task is to ensure foundation reliability on permafrost but also decrease the construction and operation expenses due to optimization of adopted decisions. Forecast modeling of soil bases temperature regime is required for this. Analysis of norms and standards showed the absence of standardized requirements to the calculations algorithm.The article is devoted to the main problems of forecast modeling of soil base temperature regime and mistakes in selecting of thermal stabilization solutions. We give the examples of optimization of thermal stabilization solutions. Also, we determine the ways to solve the identified problems; these include typification of engineering and geocryological conditions, typification of structures by intensity of thermal influence, selecting of optimal thermal stabilization solutions for each type, standard elaboration of making forecast modeling of soil base temperature regime.

Calculation methods of non-stationary temperature fields influence on foundation in cryolithozone

  This article is devoted to the mathematical modeling and computing experiment in problems of temperature fields forecast in continuous foundations in cryolithozone, which will provide a qualitative approach to non-stationary thermal calculations for making design decisions to ensure the stability and reliability of bases and foundations of buildings in the Arctic zone.  The article formulates the problem of forecasting by determining changes in the temperature, areal distribution, thickness, and vertical structure of permafrost, seasonal and perennial freezing of the soil, their temperature strength state, and properties in connection with the construction of buildings. Presented mathematical calculations are based mainly on the assumption of a non-stationary process of heat exchange. Mathematical models for determining depth of thawing are considered. The problem of determining the temperature in the basement of the foundation, limited on the one side, in which the temperature depends on only one coordinate with the condition that the surface temperature of the permafrost soil undergoes periodic fluctuations around zero value under the influence of external influences, has been solved. It is demonstrated that the two-dimensional problem of permafrost ground with a semi-infinite foundation thickness can be generalized even more. The problem is formulated in the form of a differential equation of heat balance taking into account the heat flux, which varies according to the Fourier’s law.  

The glacial origins of relict ‘pingos’, Wales, UK

Ramparted depressions (doughnut-shaped debris-cored ridges with peat- and/or sediment-filled central basins) are commonly perceived to represent the relict collapsed forms of permafrost ground-ice mounds (i.e. pingos or lithalsas). In Wales, UK, ramparted depressions of Late Pleistocene age have been widely attributed to permafrost-related processes. However, a variety of alternative glacial origins for these enigmatic landforms are also consistent with the available geological and geomorphological evidence, although previous studies have barely considered such alternative processes of formation. From detailed geophysical, sedimentological and remote-sensing studies at two field sites, we demonstrate that: (i) the wastage of stagnating glacier ice is a viable alternative explanation for the formation of ramparted depressions in Wales; (ii) the glacial geomorphology and geology of these landforms is analogous to supraglacial and subglacial landforms from the last Laurentide and Fennoscandian ice sheets; (iii) these landforms have significant potential for characterising the nature of deglaciation around the margins of the Irish Sea during the last glacial cycle, and may record evidence for the overextension and stagnation of the south-eastern margin of the Irish Sea Ice Stream; and (iv) investigations of ramparted depressions within formerly glaciated terrains must consider both glacial and periglacial mechanisms of formation.