Abstract
Artificial perturbations of borehole water levels, known as slug tests, are a useful means of characterizing the glacier hydrologic system. Slug tests were performed on Bench Glacier, Alaska, in 21 boreholes over three field seasons during the transition from a winter to a summer drainage mode. Fifty‐four slug tests were conducted, with water level monitoring in up to five boreholes adjacent to the slugged borehole. Seven of the slug tests were performed in conjunction with dye dispersion tests to identify water pathways within the slugged borehole following perturbation. Nearly 60% of monitored adjacent boreholes showed a hydraulic connection to the slugged borehole via the glacier bed. The nature and degree of connectivity was temporally variable, suggesting that the drainage network at the bed was highly dynamic on a daily timescale and spatial scale of tens of meters. The variability of slug test responses over time and space limit the feasibility of six alternative explanations for the oscillatory water level behavior characteristic of the underdamped response. We propose a seventh, that is, that coherent air packages are a reasonable means of producing the compliance needed to generate the underdamped slug test responses on Bench Glacier, and that these air packages may exist within the glacier at the tips of subglacially propagated fractures.
Highlights
[2] Increased surface melting of snow and ice masses in a glacier setting can alter the subglacial hydrology by increasing the amount of water routed to the bed
[3] The slug test involves artificially perturbing the static water level in a well or borehole and measuring the response to that perturbation. These tests are conducted by either injecting a volume of water in the well or borehole, or inserting and removing a sealed pipe to induce an instantaneous change in water level
He found oscillatory responses were induced when (1) a suspected englacial cavity was intersected during drilling and (2) the water level was perturbed by submerging the drill tip in the borehole
Summary
[2] Increased surface melting of snow and ice masses in a glacier setting can alter the subglacial hydrology by increasing the amount of water routed to the bed. [3] The slug test involves artificially perturbing the static water level in a well or borehole and measuring the response to that perturbation. Borehole dye tracing was incorporated in seven of the slug tests to isolate borehole water flow dynamics during the slug response. Using these data, we evaluate the feasibility of various mechanisms for generating underdamped water level curves, and offer air compression as a new means of producing oscillatory responses. Kulessa and Hubbard [1997] conducted 116 slug and bail tests at Haut Glacier d’Arolla, Switzerland, and used these data to derive representative subglacial sediment transmissivities with techniques frequently used in aquifer settings [Kulessa et al, 2005]. Tests were conducted over a $1 month period in each field season to capture daily
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
