Post-wildfire surface deformation near Batagay, Eastern Siberia,
detected by L-band and C-band InSAR
Abstract
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.