Alaska Section, American Water Resources Association

Michael R. Lilly, Alaska Section AWRA Northern-Region Director

I would like to invite you to the November 1998 Brown-Bag presentation by Kenji Yoshikawa, Water and Environmental Research Center, University of Alaska Fairbanks. Please note this meeting is the second Wednesday in November. Kenji's talk will be a presentation on his recent research on hydrologic processes associated with Pingos. We look forward to seeing you. Please feel free to bring a colleague to the meeting.


November 11, 1998
Alaska Section AWRA, Northern-Region Brown-Bag Presentation
Alaska Department of Natural Resources, Large Conference Room
Noon to 1300


"The Groundwater Hydraulics of Open System Pingos "
Kenji Yoshikawa
Water and Environmental Research Center, University of Alaska Fairbanks


ABSTRACT

The characteristics of spring water from open-system pingos in interior Alaska and Svalbard were examined to elucidate the relationship of groundwater with open system pingos. Water from springs under pingos creates a variety of icing blister formations in the winter. This research concluded that, pingo formation pressure varied from pingo to pingo, with artesian pressure sometimes less than 20 kPa. The pressure from ice crystallization is one of the important factors for pingo growth when artesian pressure was low. Springs warmer than 3°C or with discharge rates greater than 3 liters per second did not have pingos associated with them. Experimental evidence indicates that in order for pingo growth to occur, heat transferred to the pingo through groundwater discharge must be less than 37 kW. Also I will talk about making pingo inventory in Alaska.

INTRODUCTION

There are two general types of pingos: open-system and closed-system pingos. An open system pingo is "open" to groundwater (the source of water is not immediately adjacent to the pingo, but moves to the pingo through a regional groundwater aquifer), whereas a closed system pingo is "closed" with respect to groundwater (the souce of water is limited to supply adjacent to the pingo)(Müller, 1959). Mackay (1979) described the Tuktoyaktuk Peninsula area as "closed." However, the terms open and closed are ambiguous when applied to the Tuktoyaktuk Peninsula area pingos, and probably to those of many other areas. If water comes from a distant elevated source then the pingo is a hydraulic system pingo. If water moves under hydrostatic pressure from local permafrost aggradation, then the pingo is a hydrostatic system pingo. Therefore, the terms "hydraulic" and "hydrostatic" are probably more accurate than "open" or "closed." However, "open system" and "closed system" are terms used more commonly, and thus, this paper will use them too. Müller (1959) attempted to calculate the total updoming pressure and explain the open-system pingo developed by groundwater supply. It is generally accepted that pingos need between 600 and 2200 kPa of pressure to develop in East Greenland. However, Müller calculated the approximate heaving pressure of Trout Lake pingo in East Greenland to be 500 -600 kPa. Müller's (1959) work serves as a basis of theory for the formation of open-system pingos. Berezantsev (1947) measured the maximum tensile strength of overlying permafrost to be 250 - 1800 kPa. Pingo development was affected by gravity and the strength of the overlying material. The ice crystallization pressure was 4000 kPa at an ice temperature of -0.3°C. However, growth mechanisms are still poorly understood. Spring discharge is sometimes associated with the occurrence of open-system pingos. Thus one approach that has been utilized in a few previous studies of open-system pingos is the analysis of spring geochemistry to characterize ground water origin (e.g. O'Brien, 1971). However, the physical characteristics of open-system pingos with springs have require future investigation.

In the winter, groundwater discharge increases hydraulic potential in the active layer as the soils freeze-back. Icing blisters are seasonal frost features, which develop in response to natural discharge of ground water throughout the winter. Pollard and French (1984) measured pressure potentials of a number of icing blisters in North Fork Pass, Yukon Territory Canada. The pressures varied between 30 and 81 kPa. In East Greenland, Washburn (1969) reported a continuous discharge of sub-permafrost water at 170 kPa.