During 2008 the Alaska Division of Geological & Geophysical Surveys (DGGS) conducted reconnaissance interpretive mapping of permafrost in Alaska Highway Corridor Segment 2, a 12-mi-wide (19.3-km-wide) corridor that straddles the Alaska Highway through the upper Tanana River valley from the eastern boundary of the Mt. Hayes Quadrangle to the eastern edge of the Tanacross Quadrangle. This work was an extension of permafrost mapping done in Alaska Highway Corridor Segment 1 from Delta Junction to Dot Lake in the Big Delta and Mt. Hayes Quadrangles during 2006-2007. Primarily, we inferred the extent of permafrost and ice content by interpreting ~1:65,000-scale, false-color infrared aerial photographs taken in July 1978, August 1980, and July 1983.

During 2006 and 2007 the Alaska Division of Geological & Geophysical Surveys conducted reconnaissance interpretive mapping of permafrost in Alaska Highway Corridor Segment 1, which straddles the Alaska Highway through the Tanana River valley from Delta Junction to the eastern boundary of the Mt. Hayes Quadrangle. Primarily, we inferred the extent of permafrost and ice content by interpreting ~1:63,360-scale, false-color infrared aerial photographs taken in August 1980.

Alaska Division of Geological & Geophysical Surveys (DGGS) has conducted 1:63,360-scale geologic mapping of the Sagavanirktok B-1 Quadrangle (640 square km�equivalent to four 7.5 minute quadrangles). This mapping project reinterprets micropaleontologic correlations for 17 Sagavanirktok Quadrangle wells, and reprocesses data from the one publicly-available seismic line. Surface geologic mapping, subsurface-to-surface stratigraphic age control, and seismic framework are required to reliably decipher the complex geology of this key area of the Brooks Range. Outcrops within the Sagavanirktok B-1 Quadrangle are the closest surface expressions of Prudhoe Bay source and reservoir rocks. This study yields critical petroleum-related information from these surface exposures, and how they relate to the area subsurface stratigraphy.

Geophysical measurements were collected by the U.S. Geological Survey (USGS) at five sites in Interior Alaska in September 2021 for the purposes of imaging permafrost structure and quantifying variations in subsurface moisture content in relation to thaw features. Electrical resistivity tomography (ERT) measurements were made along transects 110-222 meters (m) in length to quantify subsurface permafrost characteristics. ERT transects were collected across a fireline boundary within the Bonanza Creek Long Term Ecological Research (LTER) site where repeat measurements have been made since 2014; across and adjacent to two thermokarst lakes, Vault Lake and Goldstream Lake; and along two profiles at the North Star golf course in Fairbanks, Alaska. Models of electrical resistivity produced from these data revealed the distribution of frozen and thawed soil to depths of 10-40 m below the surface. Borehole nuclear magnetic resonance (NMR) data were collected at two sites in order to determine liquid water content at depth in shallow boreholes. NMR data were collected in a 2.25 m-deep borehole at the North Star golf course adjacent to one of the ERT profiles, and in another two 1.625 m-deep boreholes adjacent to Big Trail Lake where previous NMR measurements were made in 2019 and 2020. Manual permafrost-probe measurements of thaw depths were collected at set intervals along each ERT transect and adjacent to NMR measurement locations used for comparison to the geophysical measurements, except at the North Star golf course where shallow permafrost was absent.

Geophysical measurements were collected by the U.S. Geological Survey (USGS) at five sites in Interior Alaska in September 2021 for the purposes of imaging permafrost structure and quantifying variations in subsurface moisture content in relation to thaw features. Electrical resistivity tomography (ERT) measurements were made along transects 110-222 meters (m) in length to quantify subsurface permafrost characteristics. ERT transects were collected across a fireline boundary within the Bonanza Creek Long Term Ecological Research (LTER) site where repeat measurements have been made since 2014; across and adjacent to two thermokarst lakes, Vault Lake and Goldstream Lake; and along two profiles at the North Star golf course in Fairbanks, Alaska. Models of electrical resistivity produced from these data revealed the distribution of frozen and thawed soil to depths of 10-40 m below the surface. Borehole nuclear magnetic resonance (NMR) data were collected at two sites in order to determine liquid water content at depth in shallow boreholes. NMR data were collected in a 2.25 m-deep borehole at the North Star golf course adjacent to one of the ERT profiles, and in another two 1.625 m-deep boreholes adjacent to Big Trail Lake where previous NMR measurements were made in 2019 and 2020. Manual permafrost-probe measurements of thaw depths were collected at set intervals along each ERT transect and adjacent to NMR measurement locations used for comparison to the geophysical measurements, except at the North Star golf course where shallow permafrost was absent.

Geophysical measurements were collected by the U.S. Geological Survey (USGS) at two sites in Interior Alaska in 2019 and 2020 for the purposes of imaging permafrost structure and quantifying variations in subsurface moisture content in relation to thaw features. In September 2019, electrical resistivity tomography (ERT) and downhole nuclear magnetic resonance (NMR) data were used to quantify permafrost characteristics across the shorelines of Big Trail Lake, a thermokarst lake outside of Fairbanks, Alaska. Three 222 m ERT survey lines were collected perpendicular to the North, East, and South shorelines, and two 110 m lines were collected parallel to the southeast and northeast shorelines. Models of electrical resistivity produced from these data revealed the distribution of frozen and thawed soil to depths of 10-40 m below the surface. NMR data were collected within two 2.3 m deep boreholes adjacent to the East and North perpendicular ERT survey lines in September 2019 and logged again in March 2020. Additional one-time NMR measurements of liquid water content were collected in September 2019 within the lakebed sediments (0-25 cm depth) in approximately 2.5 m lateral increments moving away from the shorelines in the East and North, between 0 and 12 m from shore. These NMR transects roughly coincided with the perpendicular ERT lines. A separate ERT survey was conducted at the Bonanza Creek LTER (Long Term Ecological Research) in September 2019 and was a repeat of a previous ERT survey done in the same exact location three years prior. The survey line was 125 m in length and spanned the transition between burned and unburned forest. Models of electrical resistivity for this site imaged the structure of frozen and thawed soils to depths of 10-15 m. At both sites, manual permafrost-probe measurements of thaw depths were collected at set intervals along each ERT transect and used for comparison to the resistivity models.

Geophysical measurements and related field data were collected by the U.S. Geological Survey (USGS) at the Alaska Peatland Experiment (APEX) site in Interior Alaska from 2018 to 2020 to characterize subsurface thermal and hydrologic conditions along a permafrost thaw gradient. The APEX site is managed by the Bonanza Creek LTER (Long Term Ecological Research). In April 2018, seven boreholes were emplaced to depths of 2.3-2.5 meters (m) to allow for repeat logging with downhole nuclear magnetic resonance (NMR) to quantify the spatial and temporal variations in unfrozen water content within active-layer and permafrost soils. NMR data were collected on ten separate occasions between April 2018 and October 2020. In June 2018, soil temperature and moisture sensors were installed at select locations and depths across the study site to record point-scale temperature and moisture conditions in 30 minute intervals. In August 2018, electrical resistivity tomography (ERT) data were collected along four 82 m-long transects. Models of electrical resistivity produced from these data revealed the spatial variability in soil lithology and thermal state (frozen vs. thawed) to depths up to 10-15 m below the surface. Lastly, manual permafrost-probe measurements of thaw depths were collected at each instrument location during summer site visits for comparison to the geophysical data.

Geophysical measurements and related field data were collected by the U.S. Geological Survey (USGS) at the Alaska Peatland Experiment (APEX) site in Interior Alaska from 2018 to 2020 to characterize subsurface thermal and hydrologic conditions along a permafrost thaw gradient. The APEX site is managed by the Bonanza Creek LTER (Long Term Ecological Research). In April 2018, seven boreholes were emplaced to depths of 2.3-2.5 meters (m) to allow for repeat logging with downhole nuclear magnetic resonance (NMR) to quantify the spatial and temporal variations in unfrozen water content within active-layer and permafrost soils. NMR data were collected on ten separate occasions between April 2018 and October 2020. In June 2018, soil temperature and moisture sensors were installed at select locations and depths across the study site to record point-scale temperature and moisture conditions in 30 minute intervals. In August 2018, electrical resistivity tomography (ERT) data were collected along four 82 m-long transects. Models of electrical resistivity produced from these data revealed the spatial variability in soil lithology and thermal state (frozen vs. thawed) to depths up to 10-15 m below the surface. Lastly, manual permafrost-probe measurements of thaw depths were collected at each instrument location during summer site visits for comparison to the geophysical data.

40Ar/39Ar analyses of igneous rocks from the Alaska Highway corridor between Delta Junction and the Canada border show a range of Cretaceous ages from about 68 Ma to about 112 Ma. The 25 samples fall into two broad age groups. The younger group ranges from about 68 Ma to 73 Ma; the older group ranges from a minimum age of about 84 Ma to about 103 Ma. One sample, a mafic dike, yielded an older age of about 112 Ma.

Borehole nuclear magnetic resonance (NMR) data were collected by the U.S. Geological Survey (USGS) at Big Trail Lake, a thermokarst lake outside of Fairbanks, Alaska, to quantify unfrozen water content and soil properties at select sites in and around the lake edge. In September 2019, NMR data were collected within two 2.3 m deep boreholes adjacent to the East and North perpendicular electrical resistivity survey lines. Manual permafrost-probe measurements of thaw depths were also collected. These two boreholes were logged a second time in late March 2020. Additional one-time NMR measurements of liquid water content were collected in September 2019 within the lakebed sediments (0-25 cm depth) in approximately 2.5 m lateral increments moving away from the shorelines in the East and North, between 0 and 12 m from shore. These NMR transects roughly coincided with the perpendicular electrical resistivity lines.