The influence of permafrost on high latitude river and lake dynamics.
IPGP - Îlot Cuvier
Séminaires de Potamologie
Earth & Environmental Sciences Division, Los Alamos National Laboratory
In many arctic river systems, permafrost and the presence of frozen floodplain materials provides a significant source of bank cohesion. Due to this cohesion, permafrost may play an important control on arctic river mobility and meandering dynamics. Whether changes in the rates of permafrost thawing has had or will have a significant geomorphic impact on arctic rivers dynamics is at present an unanswered question. The potential impact of climate-driven changes on arctic riverbank erosion has important implications for river mobility, planform morphology, floodplain dynamics, river ecology, and the export of carbon and nutrients to coastal oceans. We have conducted remote sensing analysis of river mobility for the Yukon and Selawik Rivers in Alaska and sections of the Siberian Rivers including the Ob, Kolyma, Yana and the Indigirka Rivers. Over the period of Landsat coverage (mid-1980s to present) the majority of the banks on these rivers show limited to no movement at the resolution of the Landsat data (30 m per pixel). Where eroding, the mean annual rates showed very limited variability across river systems (3.5 to 6.5 m/yr) despite river widths ranging from 70 to 1800 m, suggesting that the rate of permafrost thaw may represent an upper limit to bank erosion rates in these systems. In addition to the significant spatial variability in erosion rates, field observations suggest that riverbank erosion is highly variable in time. On the small (70 m wide) Selawik River in Alaska, no observable bank erosion occurred in 2010, but in 2011 an entire year’s worth of erosion occurred over the course of approximately 5 days coincident with spring snow melt flood peak. For the remainder of the year erosion rates on this system appear to be limited by fluvial not thermal controls. Based on these observations we hypothesize that arctic riverbank erosion varies in space and time between transport-limited to thaw-limited conditions. How these river systems will respond to climate change will likely depend on a complex interaction between river hydrology and the thermal dynamics of permafrost thaw. Changes the sizes and distributions of Arctic and Subarctic lakes and ponds over the last 50 years has been cited as evidence for permafrost degradation. Using a coupled heat and groundwater flow model, we investigated the influence of sub-permafrost groundwater and advective heat transport on the stability of permafrost and its response to thermal disturbance. Our simulations indicate that inclusion of groundwater and advective heat transport leads to permafrost thicknesses two to five times thinner than predictions with conductive heat transport alone. Additionally, our simulations examining the thermal influence of lakes on underlying permafrost suggest that a through?going talik (permanently thawed ground) can develop in a matter of decades and that the incorporation of advective heat transport reduces the time to complete loss of ice beneath the lake by half, relative to heat transport by conduction alone.