Thaw depths beneath arctic streams may have significant impact on the seasonal development of hyporheic zone hydraulics. To investigate thaw progression over the 2004 summer season we acquired a series of ground-penetrating radar (GPR) profiles at five sites from May–September, using 100, 200 and 400 MHz antennas. We selected sites with the objective of including stream reaches that span a range of geomorphologic conditions on Alaska's North Slope. Thaw depths interpreted from GPR data were constrained by both recorded subsurface temperature profiles and by pressing a metal probe through the active layer to the point of refusal. We found that low-energy stream environments react much more slowly to seasonal solar input and maintain thaw thicknesses longer throughout the late season whereas thaw depths increase rapidly within high-energy streams at the beginning of the season and decrease over the late season period. Copyright © 2006 John Wiley & Sons, Ltd.