The massive flooding of the Sagavanirktok River in northern Alaska in 2015 not only had immediate impacts, but also led to longer-term ground subsidence in the permafrost-rich region. This groundbreaking research, conducted by assistant professor Simon Zwieback and a team of scientists from the University of Alaska Fairbanks Geophysical Institute, sheds light on the previously unknown effects of flooding on tundra and permafrost landscapes. The study, published in the journal Permafrost and Periglacial Processes, highlights the importance of understanding how these landscapes react to floods, especially in a changing climate.
The Flood Event
In mid-May 2015, floodwaters spilled onto the Dalton Highway, which serves as the road to the North Slope of Alaska. The flooding also affected Deadhorse airport. The chaotic nature of the flood was attributed to a pre-flood buildup of aufeis, layered ice formed from the freezing of river water. Aufeis diverted the thawing river’s water away from natural channels, exacerbating the flood’s impact. The study also suggests that human activity in the area, driven by the expansion of the Prudhoe Bay oilfield and the presence of the Dalton Highway, has interfered with natural drainage, contributing to the severity of the flooding.
The Subsidence Phenomenon
The research team analyzed satellite data from 2015 to 2019 to track ground deformation in the years following the flood. They found widespread but variable subsidence, with the most pronounced effects occurring in flooded areas and during the two years after the flood. The study attributes the subsidence primarily to the melting of ground ice, which is abundant in the area in the form of ice wedges and segregated ice. The initial subsidence triggers changes at the surface, including water ponding, which leads to increased thawing underneath. This, in turn, causes further subsidence and alters surface conditions.
Factors Driving Deformation
The subsidence observed in the study was not consistent across all areas with high ice content. Multiple factors contribute to ground deformation, including disturbance to the organic layer and sediment deposition. The deposition of sediment settles into the soil, reducing its insulating air pockets and allowing more heat to penetrate. Although the researchers found fine-grain sediment in the topsoil, they could not definitively attribute it to the flood event. However, it is clear that both organic layer disturbance and sediment deposition play a role in the subsidence process.
While flooding can have immediate negative consequences, such as ground subsidence, the study also highlights its potential long-term benefits. Flooding deposits sediment, which increases the insulating vegetation cover and organic matter in the area. Over time, this results in the thinning of the active layer, allowing for the growth of ice wedges and segregated ice. The elevation increases, reducing the frequency of future floods. Understanding these long-term effects is crucial as the Arctic faces increasing climate stress and changing flood regimes.
As the Arctic region becomes wetter and experiences climate change, it is vital to comprehend how riverine landscapes respond to these shifts. The research conducted by Zwieback and his team provides valuable insights into the complex interactions between floods and permafrost landscapes. These findings contribute to our understanding of the impacts of flooding and the potential consequences for communities and infrastructure in Arctic regions.
The 2015 flooding of the Sagavanirktok River in northern Alaska had both immediate and long-term impacts on the permafrost-rich region. Through satellite data analysis, the research team discovered widespread subsidence, particularly in flooded areas, in the two years following the flood. The melting of ground ice, disturbance to the organic layer, and sediment deposition were identified as factors driving deformation. While flooding has negative consequences, it also brings long-term benefits, such as increased elevation and reduced flood frequency. Understanding how riverine landscapes respond to floods is crucial in the face of ongoing climate change in the Arctic. The study by Zwieback and his team provides valuable insights into these complex processes and highlights the importance of considering the effects of flooding on the delicate balance of Arctic ecosystems.