Disparate permafrost terrain changes after a large flood observed from space

• Published in: Permafrost and Periglacial Processes
• Main Authors: Zwieback, Simon, McClernan, Mark, Kanevskiy, Mikhail, Jorgenson, Mark T., Walker, Donald A., Chang, Qianyu, Bergstedt, Helena, Toniolo, Horacio, Romanovsky, Vladimir E., Meyer, Franz J.
• Other Authors: National Aeronautics and Space Administration, Directorate for Biological Sciences, National Geospatial-Intelligence Agency
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2023
• Subjects: Arctic; Ice; permafrost; Permafrost and Periglacial Processes; Prudhoe Bay; Tundra; wedge*; Alaska
• Online Access: http://dx.doi.org/10.1002/ppp.2208; https://onlinelibrary.wiley.com/doi/am-pdf/10.1002/ppp.2208; https://onlinelibrary.wiley.com/doi/pdf/10.1002/ppp.2208

Abstract The 2015 spring flood of the Sagavanirktok River inundated large swaths of tundra as well as infrastructure near Prudhoe Bay, Alaska. Its lasting impact on permafrost, vegetation, and hydrology is unknown but compels attention in light of changing Arctic flood regimes. We combined InSAR and optical satellite observations to quantify subdecadal permafrost terrain changes and identify their controls. While the flood locally induced quasi‐instantaneous ice‐wedge melt, much larger areas were characterized by subtle, spatially variable post‐flood changes. Surface deformation from 2015 to 2019 estimated from ALOS‐2 and Sentinel‐1 InSAR varied substantially within and across terrain units, with greater subsidence on average in flooded locations. Subsidence exceeding 5 cm was locally observed in inundated ice‐rich units and also in inactive floodplains. Overall, subsidence increased with deposit age and thus ground ice content, but many flooded ice‐rich units remained stable, indicating variable drivers of deformation. On average, subsiding ice‐rich locations showed increases in observed greenness and wetness. Conversely, many ice‐poor floodplains greened without deforming. Ice wedge degradation in flooded locations with elevated subsidence was mostly of limited intensity, and the observed subsidence largely stopped within 2 years. Based on remote sensing and limited field observations, we propose that the disparate subdecadal changes were influenced by spatially variable drivers (e.g., sediment deposition, organic layer), controls (ground ice and its degree of protection), and feedback processes. Remote sensing helps quantify the heterogeneous interactions between permafrost, vegetation, and hydrology across permafrost‐affected fluvial landscapes. Interdisciplinary monitoring is needed to improve predictions of landscape dynamics and to constrain sediment, nutrient, and carbon budgets.