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Case History | Sweden

Storglaciären Glacier

In 2005-2006, GEOKON manufactured a custom-designed combination borehole inclinometer/digital compass for use in uncased, water-filled boreholes in glacier ice for Peter Moore and Neal Iverson from Iowa State University’s Department of Geological & Atmospheric Sciences. Over the course of the 3-year project funded by the U.S. National Science Foundation, Peter and Neal have been studying the front of a small valley glacier called Storglaciären in the northern mountains of Arctic Sweden. They are interested in how the observed motion at the surface of the glacier is partitioned between slip at the base of the ice and deformation within the ice. In the past, it was inferred that basal slip is negligible beneath the cold front of Storglaciären, and other glaciers like it, and that the ice should adhere to its substrate.

In July and August of 2007, six vertical boreholes were drilled around the wet-to-frozen-based transition in the glacier—in ice ranging from 19 m to 41 m thick—and surveyed with the inclinometer/compass probe. Anchors were then lowered on wires to the bottom of each borehole and allowed to freeze in-place, with the wires. When they returned in 2008, they re-melted the boreholes by attaching a drill nozzle to the cable, which followed the cable back down to the base of the hole.

The assumption was made that, during the one-year period between surveys, the displacement of the top of the borehole was due either to shearing of the ice itself, or to slip of the ice over its substrate. Peter and Neal used the borehole inclinometry results to estimate the proportion of these two active processes at any point on the glacier. To their surprise, the inclinometry data indicated that internal deformation of the ice accounted for less than 30% of the surface motion, even at the cold front of the glacier. This finding is corroborated by a finite element model of the glacier front, suggesting that even though the ice may be frozen to the top of the bed, the bed (likely composed of glacial till) is deforming beneath the ice and allowing the glacier front to slide without great resistance.

GEOKON extends a special "Thanks" to Peter and Neal for sharing their results with us:

Peter Moore and Neal Iverson

Department of Geological & Atmospheric Sciences,

Iowa State University

Photo of Storglaciären Glacier.
The Model 6000-1MX:

A custom-designed combination borehole inclinometer / digital compass.