5:15 PM - 6:30 PM
[ACG39-P07] Thermokarst settlement in Churapcha, eastern Siberia, detected by ALOS-2 InSAR
Keywords:Permafrost, Thermokarst, InSAR, ALOS-2
Thermokarst is an irreversible phenomenon accompanying topographic changes due to ground ice melting in Yedoma landscape containing large ice volume, which has been observed in eastern Siberia and Alaska. Lena-Aldan interfluvial area in central Yakutia in eastern Siberia is now facing extensive development of landscape with surface subsidence due to thermokarst development during past decades. Damage on infrastructure due to surface subsidence and changes in water balance and ecosystem could affect lives of neighbors. Churapcha, where is located about 140 km east of Yakutsk, is one of typical residential areas facing recent thermokarst development. Saito et al. (2018) generated detailed topographic maps on disused airfield and abandoned arable land by unmanned aerial systems, and estimated surface subsidence rate from 1990. However, there has been no systematic observation of surface subsidence on entire Churapcha area so far. In order to predict further thermokarst development and to minimize the impact of permafrost degradation on neighbors, it is important to quantify the current rate of thermokarst and its spatial variation.
In this study, InSAR analysis using spaceborne synthetic aperture radar (SAR) data were conducted using six scenes of ALOS-2 L-band data acquired in 2015-2020. We generated 15 interferograms and selected 11 of them excluding interferograms which the image acquisition period of the pair is over four years or the same year. Stacking was applied to the selected interferograms to derive averaged displacement rate in 2015-2020. The reference point at each interferogram was set to one of alasses on southeast from the Churapcha residential area. Alas is final geomorphological stage of thermokarst development and we assumed that inter-annual displacement at alas is less likely than its surroundings.
As the result of the InSAR analysis, we identified major subsidence at arable lands (T1 and T2) located on north of the residential area, and grasslands on west (T3) and south (T4 and T5) of the residential area. The magnitude of the subsidence rate was up to 2.4 cm/yr. Numerous high-centered polygonal reliefs in the areas were identified by high resolution optical images obtained by WorldView-2/-3/-4. According to land-use changes between 1945 and 2009 (Gorokhov et al., 2011), the places of T1 and T2 were changed from grassland in 1945 to arable land in 2009. Furthermore, the two places are located a few tens of meters higher than alasses surrounding the residential area, which implies that there is a possibility of remaining unthawed ground ice under the places. We have considered that thermokarst in the T1 and T2 has developed more rapidly than the surrounding areas by changes of impact on ground ice from solar radiation and water balance due to loss of vegetation by the land-use change. However, there is little surface subsidence in an arable land located a few kilometers east of the T1 and T2 although polygonal relief was identified as well as the T1 and T2. We speculate the possibility of different subsidence rate dependent on how the land surface is preserved even the same land use. On the other hand, detected thermokarst subsidence of the T3-T5 in grassland did not change in land-use during the period. These places have been considered to be influenced by recent climate changes (increase of air/ground temperature, change of water balance).
In this study, InSAR analysis using spaceborne synthetic aperture radar (SAR) data were conducted using six scenes of ALOS-2 L-band data acquired in 2015-2020. We generated 15 interferograms and selected 11 of them excluding interferograms which the image acquisition period of the pair is over four years or the same year. Stacking was applied to the selected interferograms to derive averaged displacement rate in 2015-2020. The reference point at each interferogram was set to one of alasses on southeast from the Churapcha residential area. Alas is final geomorphological stage of thermokarst development and we assumed that inter-annual displacement at alas is less likely than its surroundings.
As the result of the InSAR analysis, we identified major subsidence at arable lands (T1 and T2) located on north of the residential area, and grasslands on west (T3) and south (T4 and T5) of the residential area. The magnitude of the subsidence rate was up to 2.4 cm/yr. Numerous high-centered polygonal reliefs in the areas were identified by high resolution optical images obtained by WorldView-2/-3/-4. According to land-use changes between 1945 and 2009 (Gorokhov et al., 2011), the places of T1 and T2 were changed from grassland in 1945 to arable land in 2009. Furthermore, the two places are located a few tens of meters higher than alasses surrounding the residential area, which implies that there is a possibility of remaining unthawed ground ice under the places. We have considered that thermokarst in the T1 and T2 has developed more rapidly than the surrounding areas by changes of impact on ground ice from solar radiation and water balance due to loss of vegetation by the land-use change. However, there is little surface subsidence in an arable land located a few kilometers east of the T1 and T2 although polygonal relief was identified as well as the T1 and T2. We speculate the possibility of different subsidence rate dependent on how the land surface is preserved even the same land use. On the other hand, detected thermokarst subsidence of the T3-T5 in grassland did not change in land-use during the period. These places have been considered to be influenced by recent climate changes (increase of air/ground temperature, change of water balance).