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    Understanding permafrost dynamics and geohazards with a terrain-cryofacies approach

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    Name:
    Stephani_E_2021.pdf
    Embargo:
    2023-12-03
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    46.66Mb
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    Author
    Stephani, Eva
    Chair
    Shur, Yuri
    Doré, Guy
    Committee
    Darrow, Margaret
    Kanevskiy, Mikhail
    Keyword
    Permafrost
    Colville River Delta
    Erosion
    Thermokarst
    Metadata
    Show full item record
    URI
    http://hdl.handle.net/11122/13004
    Abstract
    The Arctic and its permafrost terrain are inherently dynamic, complex, and sensitive environments. Understanding the past and current changes occurring in these systems is key in predicting future variations, including the response of permafrost to climate change, and to terrain modifications resulting from natural processes or anthropogenic activities. This study contributes to advance our understanding of permafrost dynamics in varying permafrost environments of northern Alaska and northwestern Canada using a terrain-cryofacies approach. This unique approach helps to increase our understanding of permafrost dynamics from the site-specific scale to over extended areas by recognizing linkages between terrain and subsurface properties, and by identifying similar terrain units in remote sensing analysis. In the Colville River Delta (Alaska), our terrain-cryofacies study integrated data from 79 boreholes with a remote sensing analysis to evaluate the temporal changes in the Nigliq channel positions from 1948 to 2013 and the related permafrost dynamics. Most land cover changes occurred as land exposition (64%), whereas about 36% of the total changes were classified as eroded. The erosion of the older terrain units from the floodplain toposequence, such as the inactive-floodplain cover deposits, implied ground loss volumes of about one-fifth of soil solids and four-fifths of ground ice. Along this channel, we also identified the typical configuration and properties of taliks and cryopegs, as well as subsequent epigenetic permafrost growth. We found that the active channel was underlain by closed taliks, rather than through taliks and thus did not penetrate the entire layer of permafrost connecting supra- and sub-permafrost groundwater. A cryopeg connected to the active channel talik was identified from borehole data in the adjacent terrain units that developed following channel migration. We estimated the likelihood of encountering such taliks and cryopegs over extended areas. The terrain-cryofacies approach was also applied to understand permafrost dynamics of hillslope thermokarst located in multiple ecoregions of northern Alaska and northwestern Canada, including areas affected by interactions with infrastructure. Six features were studied through the combination of field-based and remote sensing methods, whereas 150 others were assessed solely by remote sensing. Studies along a pipeline indicated that embankment construction led to an increase in the active layer thickness, reaching the underlying ice-rich intermediate layer, and causing thaw settlement. This formed a thermokarst-ditch that facilitated channelization of cross-drainage water, and thermal erosion of the ice-rich permafrost that became affected by thermal denudation and caused a retrogressive thaw slump (RTS). The RTS later selfstabilized mainly due to the lateral discontinuity of massive ice (i.e., ice wedge) and the low-relief terrain. We suggested approaches to develop adaptation strategies for infrastructure at risk of RTS based on: these findings and conditions that favor or limit RTS growth by local feedbacks; considering the interaction patterns that we identified between RTS and infrastructure; and the main destabilization processes that we highlighted by terrain units. Further research is necessary, however, and must include testing potential mitigation techniques at multiple sites with monitoring programs to assess the variability in performance with respect to site-specific conditions.
    Description
    Dissertation (Ph.D.) University of Alaska Fairbanks, 2021
    Table of Contents
    Chapter 1: Introduction. Chapter 2: Taliks, cryopegs, and permafrost dynamics related to channel migration, Colville River Delta, Alaska. Chapter 3: Assessing riverbank erosion and land cover changes in permafrost regions based on a terrain analysis approach, an example from the Colville River Delta, northern Alaska. Chapter 4: Development of retrogressive thaw slumps near infrastructure, from initiation to stabilization: an example from the Brooks Range foothills, Alaska. Chapter 5: Towards the development of adaptation strategies for infrastructure affected by thaw slumping across varying permafrost environments. Chapter 6: An overview and assessment of major engineering challenges in Canada's north. Chapter 7: Summary and conclusions. Appendices.
    Date
    2021-12
    Type
    Dissertation
    Collections
    Engineering
    Interdisciplinary Studies

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