HR: 1340h
AN: C13B-0279    [Abstracts]
TI: Time lapse imaging of thaw-bulb development beneath arctic streams using ground-penetrating radar
AU: * Brosten, T R
EM: troybrosten@mail.boisestate.edu
AF: Department of Geosciences Boise State University, 1910 University Dr MG-117, Boise, ID 83725 United States
AU: Bradford, J H
EM: johnb@cgiss.boisestate.edu
AF: Center for Geophysical Investigation of the Shallow Sursurface Boise State University, 1910 University Dr MG-206, Boise, ID 83725 United States
AU: McNamara, J P
EM: jmcnamar@boisestate.edu
AF: Department of Geosciences Boise State University, 1910 University Dr MG-117, Boise, ID 83725 United States
AU: Bowden, W
EM: breck.bowden@uvm.edu
AF: School of Natural Resources University of Vermont, 304 Aiken Center, Burlington, VT 05405 United States
AU: Gooseff, M N
EM: michael.gooseff@usu.edu
AF: Department of Aquatic, Watershed, and Earth Resources Utah State University, NR 230, Logan, UT 84322 United States
AB: We are investigating the responses of arctic tundra stream geomorphology, hyporheic zone hydrology, and biogeochemical cycling to climate change. Field results from summer, 2003, demonstrate that GPR is an effective tool for imaging the depth to sub-stream permafrost. The results presented here are the next step in the use of ground-penetrating radar (GPR) data for measuring sub-stream thaw over the summer season. We acquired a series of GPR profiles at seven sites from May - September, 2004, using 100, 200, and 400 MHz antennas. We selected sites with the objective of including stream reaches spanning a range of geomorphologic conditions in rivers and streams on Alaska's North Slope. Generally the streams can be placed into two categories: 1) as low-energy water flow with organic material lining the streambeds (peat streams) or 2) as high-energy water flow with cobble to gravel material lining the streambeds (alluvial streams). We acquired data using a pulsed radar system with high-power transmitter. Early in the field season we used the 400 and 200 MHz antennas to maximize resolution potential, then gradually shifted to the lower frequency 100 MHz antennas later in the season to increase depth of penetration. We placed the radar antennas in the bottom of a small rubber boat, then pulled the boat across the bank and through the stream while triggering at a constant interval via a string odometer system. Depth to permafrost was verified by pressing a metal probe through the active layer to the point of refusal. In addition, we recorded temperature data using thermocouples placed at varying substream depths along two of the seven GPR profiles. We used the temperature profiles to constrain and verify the GPR interpretation. At several sites we obtained excellent results and have produced images of thaw-bulb growth through the summer season in both alluvial and peat stream morphologies.
DE: 9315 Arctic region
DE: 1823 Frozen ground
DE: 1824 Geomorphology (1625)
DE: 0694 Instrumentation and techniques
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting