Construction and Deployment of Tilt Sensors along the Lateral Margins of Jarvis Glacier, Alaska to improve understanding of the Deformation Regime of Wet-Based Polythermal Glaciers
Abstract
Most studies of natural ice have been on bodies of ice with frozen beds which experience minimal lateral shear strain, to the exclusion of polythermal ice sheets & glaciers which due to their mixed basal thermal regime have wet-based beds. The deficiency in knowledge and understanding of the operative deformation mechanisms of wet-based bodies of ice results in uncertainty in the constitutive flow law of ice. Given that the flow law was derived experimentally under assumptions more conducive to bodies of ice with frozen-based beds, it is necessary to calibrate the flow law when applied to different bodies of ice such as wet-based polythermal glaciers. To this end, Dartmouth and the University of Maine have collaborated to carry out research on Jarvis Glacier in Alaska, a geometrically simple, wet-based glacier. Here, we constructed and deployed an array of 25 tilt sensors into 3 boreholes drilled along the glacier's shear margin. Our goal is to obtain 3D strain measurements to calculate the full velocity field & create deformation regime maps in the vicinity of the boreholes, as well as to support numerical modeling. The tilt sensors were developed in-lab: Each tilt sensor comes equipped with an LSM303C chip (embedded with a 3-axis accelerometer and magnetometer) and Arduino Pro-Mini mounted on a custom-made printed circuit board encased within a watertight aluminum tube. The design concept was to produce a sensor string, consisting of tilt sensors spaced apart at pre-calculated intervals, to be lowered into a borehole and frozen-in over months to collect strain data through a Campbell Scientific CR1000 datalogger. Three surface-to-bed boreholes were successfully installed with tilt sensor strings. Given the lack of prior in-situ borehole geophysics studies on polythermal glaciers, deliberate consideration on factors such as strain relief and waterproofing electrical components was necessary in the development of the sensor system. On-site challenges also arose due to the anticipated long deployment times of the sensor systems and the glacier's complex thermal structure. In addition to detailing the sensors themselves and the developmental process, we also present preliminary results from initial tilt sensor data.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2017
- Bibcode:
- 2017AGUFM.H41J1588L
- Keywords:
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- 3394 Instruments and techniques;
- ATMOSPHERIC PROCESSES;
- 0452 Instruments and techniques;
- BIOGEOSCIENCES;
- 0794 Instruments and techniques;
- CRYOSPHERE;
- 1895 Instruments and techniques: monitoring;
- HYDROLOGY