The Young’s modulusE of ice is an important parameter in models of tidal deformation [1, e.g] and in converting flexural rigidities to ice shell thicknesses [2, e.g.]. There is a disagree-ment of an order of magnitude between measurements ofE in the laboratory (9 GPa) and from field observations (≈1...
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| Format: | Text |
| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.694.1902 http://www.lpi.usra.edu/meetings/europa2004/pdf/7005.pdf |
| Summary: | The Young’s modulusE of ice is an important parameter in models of tidal deformation [1, e.g] and in converting flexural rigidities to ice shell thicknesses [2, e.g.]. There is a disagree-ment of an order of magnitude between measurements ofE in the laboratory (9 GPa) and from field observations (≈1 GPa). Here I use a simple yielding model to address this discrepancy, and conclude thatE = 9 GPa is consistent with the field obser-vations. I also show that flexurally-derived shell thicknesses for icy satellites are insensitive to uncertainties in E. Lab Measurements Because ice may creep or fracture un-der an applied stress, it behaves elastically only if the loading frequency is high and stresses are small. Lower tempera-tures expand the parameter space in which elastic behaviour is expected. The most reliable way of determining E in the lab-oratory is to measure the sound velocity in ice and thus derive the elastic constants. The values of E found are consistently about 9 GPa [3; 4]. Field Measurements Field techniques rely on observing the response of ice shelves to tidal deformation [5]. In this case, loading frequencies are much lower ( ∼ 10−5 Hz) and stresses much higher (∼1 MPa). Fractures are commonly observed, and creep is also likely to occur [6]; thus, not all of the shelf may respond in an elastic fashion. The length-scale of the response of an ice shelf to tidal deformation is determined by the parameter β [7], where: β4 = 3ρg (1 − ν2) |
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