Interpretation of borehole-inclinometer data: a general theory applied to a new instrument

Blake, Erik W.

doi:10.1017/s0022143000009655

Cited by 10 publications

(7 citation statements)

References 30 publications

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“…However, Blake and Clarke (1992) demonstrated that inclinometry may underestimate borehole tilt due to tension in the inclinometer cable, which tends to pull the top of the instrument into a more vertical orientation than the hole itself. As a result, inclinometry data provided minimum estimates of internal ice deformation and therefore yielded maximum estimates of basal velocities.…”

Section: Field Methodsmentioning

confidence: 99%

Effect of a cold margin on ice flow at the terminus of Storglaciären, Sweden: implications for sediment transport

Moore¹,

Iverson²,

Brugger

et al. 2011

J. Glaciol.

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The cold-based termini of polythermal glaciers are usually assumed to adhere strongly to an immobile substrate and thereby supply significant resistance to the flow of warm-based ice upglacier. This compressive environment is commonly thought to uplift basal sediment to the surface of the glacier by folding and thrust faulting. We present model and field evidence from the terminus of Storglaciären, Sweden, showing that the cold margin provides limited resistance to flow from up-glacier. Ice temperatures indicate that basal freezing occurs in this zone at 10 −1 -10 −2 m a −1 , but model results indicate that basal motion at rates greater than 1 m a −1 must, nevertheless, persist there for surface and basal velocities to be consistent with measurements. Estimated longitudinal compressive stresses of 20-25 kPa within the terminus further indicate that basal resistance offered by the cold-based terminus is small. These results indicate that where polythermal glaciers are underlain by unlithified sediments, ice-flow trajectories and sediment transport pathways may be affected by subglacial topography and hydrology more than by the basal thermal regime.

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Section: Field Methodsmentioning

confidence: 99%

Effect of a cold margin on ice flow at the terminus of Storglaciären, Sweden: implications for sediment transport

Moore¹,

Iverson²,

Brugger

et al. 2011

J. Glaciol.

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“…Inclinometer measurements give information on the flow field deforming the borehole axis (Hooke and others, 1987;Hubbard and others, 1998). A historical overview of different aspects of inclinometry is given by Blake and Clarke (1992).…”

Section: Introductionmentioning

confidence: 99%

Borehole logging with an eight-arm caliper–inclinometer probe

Schwerzmann

Funk

Blatter³

2006

J. Glaciol.

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A newly designed eight-arm caliper-inclinometer probe for borehole logging is presented. The caliper sounding gives eight points of cross-sections of the borehole at 1 cm intervals along its axis. Regression circles and ellipses are calculated and used as obvious hypotheses to be tested in order to obtain information on strain rates in the horizontal planes and isotropic or anisotropic borehole closure. The scratching of identifiable marks into the wall of the borehole enables material displacement to be tracked, in particular in the vertical direction, thus providing information for determining vertical strain rates along the borehole. Measurements in two boreholes drilled on high-altitude glaciers in the Swiss Alps are used to demonstrate both the potential and the limitations of the probe and of the mathematical methods presented.

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“…and Clarke [1992], and therefore can lead to overestimates of basal slip velocity. Therefore, in driving the finite element model, we begin by considering end-member scenarios for input velocities in which slidometer data give minimum basal velocities and inclinometer data give maximum basal velocities, as illustrated in Figure 4.16.…”

Section: Model Resultsmentioning

confidence: 99%

“…However, the method, when used in uncased boreholes, has larger, additional sources of error [Blake and Clarke, 1992;Harper et al, 2001]. Blake and Clarke [1992] demonstrated that inclinometry tends to underestimate borehole tilt due to tension in the inclinometer cable, which tends to pull the top of the instrument into a more vertical orientation than the hole…”

Section: Field Methodsmentioning

confidence: 99%

“…The anchor was lowered to the base of the borehole and allowed to freeze in. Extension measured by the instrument was assumed to result from vertical extension over the entire ice thickness.Englacial velocity was investigated by repeat borehole inclinometry, a method whereby the 3-dimensional trajectory of a borehole is measured two different times such that the difference in the borehole trajectory reflects the internal deformation of the ice during the intervening period [e.g.,Blake and Clarke, 1992;Harper et al, 2001]. A complete inclinometry survey was performed in new boreholes in August 2007, then repeated in the same holes after one year had elapsed.…”

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confidence: 99%

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Dynamics of ice flow and sediment transport at a polythermal glacier terminus: Storglaciaren, Sweden

Moore

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The cold-based termini of polythermal glaciers are usually assumed to adhere strongly to an immobile substrate and thereby supply significant resistance to flow of warm based ice upglacier. This compressive environment is often linked to uplift of basal sediment to the surface of the glacier by folding and thrust faulting. Herein, we present field evidence and numerical model results from the terminus of Storglaciären, Sweden, showing that the cold margin provides limited resistance to flow from upglacier. Ground-penetrating radar and thermistor data indicate that the 20-25 m thick cold surface layer meets the bed roughly 100 m from the ice margin. A heat and water balance, coupled with radar and field observations suggest that a meter-scale layer of subglacial till may be accreted in this zone. However, surface and basal velocity measurements and model results indicate that basal motion at rates

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Interpretation of borehole-inclinometer data: a general theory applied to a new instrument

Cited by 10 publications

References 30 publications

Effect of a cold margin on ice flow at the terminus of Storglaciären, Sweden: implications for sediment transport

Effect of a cold margin on ice flow at the terminus of Storglaciären, Sweden: implications for sediment transport

Borehole logging with an eight-arm caliper–inclinometer probe

Dynamics of ice flow and sediment transport at a polythermal glacier terminus: Storglaciaren, Sweden

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