Browsing University of Alaska Fairbanks by Subject "Thermokarst"
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Processes controlling thermokarst lake expansion rates on the Arctic coastal plain of Northern AlaskaThermokarst lakes are a dominant factor of landscape scale processes and permafrost dynamics in the otherwise continuous permafrost region of the Arctic Coastal Plain (ACP) of northern Alaska. Lakes cover greater than 20% of the landscape on the ACP and drained lake basins cover an additional 50 to 60% of the landscape. The formation, expansion, drainage, and reformation of thermokarst lakes has been described by some researchers as part of a natural cycle, the thaw lake cycle, that has reworked the ACP landscape during the course of the Holocene. Yet the factors and processes controlling contemporary thermokarst lake expansion remain poorly described. This thesis focuses on the factors controlling variation in extant thermokarst lake expansion rates in three ACP regions that vary with respect to landscape history, ground-ice content, and lake characteristics (i.e. size and depth). Through the use of historical aerial imagery, satellite imagery, and field-based data collection, this study identifies the controlling factors at multiple spatial and temporal scales to better understand the processes relating to thermokarst lake expansion. Comparison of 35 lakes across the ACP shows regional differences in expansion rate related to permafrost ice content ranging from an average expansion rate of 0.62 m/yr on the Younger Outer Coastal Plain where ice content is highest to 0.16 m/yr on the Inner Coastal Plain where ice content is lowest. Within each region, lakes vary in their expansion rates due to factors such as lake size, lake depth, and winter ice regime. On an individual level, lakes vary due to shoreline characteristics such as local bathymetry and bluff height. Predicting how thermokarst lakes will behave locally and on a landscape scale is increasingly important for managing habitat and water resources and informing models of land-climate interactions in the Arctic.
Sedimentology of thermokarst lakes forming within yedoma on the Northern Seward PeninsulaThermokarst lakes forming in yedoma (organic-rich permafrost containing massive syngenetic Pleistocene ice wedges) play an important role in periglacial landscape evolution. These lakes alter landscape elevation and topography, as well as redistribute upland sediment into lower basins. However, sediment deposition within yedoma thermokarst lakes is not well understood. Sedimentological, biogeochemical and macrofossil analyses enabled identification of five prominent fades in yedoma thermokarst lakes in my study region on the northern Seward Peninsula, Alaska. These include a Yedoma Taberal Silt facies situated below a sub-lacustrine unconformity, three types of basal facies and a Lacustrine Silt facies. A preliminary geomorphological model based on sediment cores from mature yedoma thermokarst lakes illustrates how fades distribution changes through the different stages of lake development. First-generation lakes (those forming in undisturbed upland) and later-generation lakes (those forming in thermokarst-affected lowland) were present on the northern Seward Peninsula. A comparison between these two lake types indicates that the depositional environments of later-generation lakes are much more variable than first-generation lakes. Understanding the depositional history and development of yedoma thermokarst lakes is critical to understanding their role in landscape evolution and the carbon cycle.