Thawing of ice-rich permafrost and subsequent ground subsidence can form characteristic landforms, and the resulting topography they create are collectively called “thermokarst”. The impact of wildfire on thermokarst development remains uncertain. Here we report on the post-wildfire ground deformation associated with the 2014 wildfire near Batagay, Eastern Siberia. We used Interferometric Synthetic Aperture Radar (InSAR) to generate both long-term (1-4 years) and short-term (sub-seasonal to seasonal) deformation maps. Based on two independent satellite-based microwave sensors, we could validate the dominance of vertical displacements and their heterogeneous distributions without relying on in-situ data. The inferred time-series based on L-band ALOS2 InSAR data indicated that the cumulative subsidence at the area of greatest magnitude was greater than 30 cm from October 2015 to June 2019, and that the rate of subsidence slowed in 2018. The burn severity was rather homogeneous, but the cumulative subsidence magnitude was larger on the east-facing slopes where the gullies were also predominantly developed. The correlation suggests that the active layer on the east-facing slopes might have been thinner before the fire. Meanwhile, C-band Sentinel-1 InSAR data with higher temporal resolution showed that the temporal evolution included episodic changes in terms of deformation rate. Moreover, we could unambiguously detect frost heave signals that were enhanced within the burned area during the early freezing season but were absent in the mid-winter. We could reasonably interpret the frost heave signals within a framework of premelting theory instead of assuming a simple freezing and subsequent volume expansion of pre-existing pore water.

The Chandler Wobble (CW) period is considered a single time-invariable constant, ~1.2 years, but the possible time-variability has not been examined using modern space-geodetic data. We first examined whether the Chandler period could vary with time on the assumption of minimum excitation power. Unexpectedly, the estimated Chandler period has been shortened by more than 60 days since about 2005. Moreover, by simple least-squares modeling, we found that CW started to be weaker in 2005 and almost disappeared in 2015. We interpret these results in both excitation and wobble domains as caused by the absence of CW for the first time in the observation history. Assuming no excitations of CW since 2005, the rather abrupt damping suggests the Q-value is below 25. Meanwhile, the analyses of the available atmospheric and oceanic angular momentum (AAM/OAM) functions indicate the significant amplitude of CW even after 2005, implying that the AAM/OAM functions are incomplete.