Abstract
Spatiotemporal variation in ground-surface displacement caused by ground freeze–thaw and thermokarst is critical information to understand changes in the permafrost ecosystem. Measurement of ground displacement, especially in the disturbed ground underlain by ice-rich permafrost, is important to estimate the rate of permafrost and carbon loss. We conducted high-precision global navigation satellite system (GNSS) positioning surveys to measure the surface displacements of tundra in northern Alaska, together with maximum thaw depth (TD) and surface moisture measurements from 2017 to 2019. The measurements were performed along two to three 60–200 m transects per site with 1–5 m intervals at the three areas. The average seasonal thaw settlement (STS) at intact tundra sites ranged 5.8–14.3 cm with a standard deviation range of 2.1–3.3 cm. At the disturbed locations, averages and variations in STS and the maximum thaw depth were largest in all observed years and among all sites. The largest seasonal and interannual subsidence (44 and 56 cm/year, respectively) were recorded at points near troughs of degraded ice-wedge polygons or thermokarst lakes. Weak or moderate correlation between STS and TD found at the intact sites became obscure as the thermokarst disturbance progressed, leading to higher uncertainty in the prediction of TD from STS.
Highlights
Frost heave is the upward or outward movement of the ground surface caused by the formation of ice lenses in porous materials (e.g., [1])
The heaved ground surface, in turn, settles during thawing seasons, and the seasonal thaw settlement (STS) depends on the amount of ice lenses formed in the previous years and the maximum thaw depth (TD) of the observation year
Our study focuses on the knowledge gap between the high-resolution spatial distribution of ground-surface displacement and remote sensing in permafrost regions
Summary
Frost heave is the upward or outward movement of the ground surface caused by the formation of ice lenses in porous materials (e.g., [1]). This is a ubiquitous phenomenon in cold regions, where the ground surface experiences freezing. The fundamental mechanism of frost heave has been recognized since the 1920s as the formation of segregated ice lenses by water migration to the freezing front in the frost-susceptible soil (e.g., [2,3]). Researchers and practitioners of civil engineering have studied the mechanism of frost heave and modeled its behavior (e.g., [5,6,7,8]) because the surface displacement damages infrastructure, such as roads, railroads, and buildings, through repeated seasonal heave and settlement. The physical processes underlying the phenomenon of frost heave have been studied by a number of researchers, as summarized by Dash et al [11]
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