APEX Thaw Depth Data from 2018-2019

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). Nine instrument sites were established in April 2018 comprising a buried seismic station for continuous passive recording of the seismic wavefield, and seven of the nine sites were given a borehole for repeat nuclear magnetic resonance (NMR) logging. Between June 2018 and September 2019, measurements of active-layer thaw depth were regularly recorded at each of the nine instrument sites for comparison to the geophysical data. A nominal four measurements were collected in random azimuthal directions within 1 meter (m) distance of the buried seismometer at each instrument site. At sites containing an NMR borehole, an additional four to six measurements were taken within 1 m distance of the borehole location. During collection of electrical resistivity tomography (ERT) data in late August 2018, additional thaw depth measurements were collected at regular electrode intervals along each ERT survey line. Measurements were made with a 250 centimeter (cm) stainless-steel frost probe inserted to the depth of refusal.