Connecting the dots…Permafrost, upwelling, and ice thickness

March 7, 2013 • Filed under: News — melanie.rohr

At this week’s seminar, Friday, March 8, 2013, WERC student Chas Jones will discuss fluctuations in groundwater flow and how these changes affect the seasonal ice dynamics on the Tanana River.

Friday Seminar Series

  • What: Connecting the dots…Permafrost, upwelling, and ice thickness
  • Who: Chas Jones
  • When: 3:30-4:30 p.m., Friday, Mar. 8
  • Where: 531 Duckering

I modeled the thermal balance between groundwater upwelling and changing ice conditions in side channel sloughs of the Tanana River near Fairbanks, a region characterized by discontinuous permafrost. Studies have linked degrading permafrost to increased winter discharge in rivers due to increasing contributions from groundwater flow. In the winter, interior Alaskan rivers are fed almost entirely by groundwater, which also serves as an external source of heat energy to the system. In fact, portions of the river fed by groundwater springs remain ice-free or have dangerously thin ice throughout the winter despite air temperatures that dip below -40° C. These areas are particularly dangerous for people that utilize Alaskan rivers for wintertime travel.
I developed a model to explore how fluctuations in groundwater discharge act as a control on river ice thickness under changing atmospheric conditions. Specifically, the model examines how local and regional changes in groundwater flow affect ice dynamics (growth or thinning) in the context of two primary research questions: 1) What are the dominant factors in the interactions of air temperature, groundwater upwelling rates, groundwater temperature, snow cover, and ice thickness in controlling the seasonal ice dynamics on the Tanana River? 2) What are the rates of change in ice thickness resulting from observed and projected changes in these parameters?
My results indicate that under a warming climate scenario, heat flux due to upwelling may degrade river ice at up to 20 mm/day. The ice melt potential is amplified by increased hydraulic gradient, hydraulic conductivity, groundwater upwelling, air temperature, groundwater temperature ice thickness, or snow depth. Increased air temperatures associated with climate change is expected to increase upwelling rates, decrease the temperature gradient, increase snow depths, and decrease ice thickness. My model indicates that potential ice melt rates may increase by up to 35% under an altered climate. These results may corroborate reports from rural Alaskans that hydrologic conditions have changed in recent decades in noticeable ways and suggest that changes associated with permafrost degradation may amplify some impacts in a warming climate.

Groundwater upwelling in Hot Cake Slough

Photo above: Groundwater upwelling in Hot Cake Slough maintains open water conditions through most of the winter despite very cold air temperatures, as evidenced in this photo with an air temperature of -30 C.

(Photo by Chas Jones)