Investigation of creep instability as a mechanism for glacier surges Page: 17 of 40
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13.-
to a basal temperature above melting point and thus creep
instability cannot occur.
To use Figure 3 to determine the stability of a given ice
mass, the values of To , vo , h,. 66, and Q must be known.
The values of y, , and 0 are calculated from equations 6.
The value of Si*, for the given y and * , is deter-
mined from Figure 3. The ice mass is stable or unstable
according as 0 is less than or greater than 2^. Table 2
shows some examples. Data sources are Budd and others (1971),
Weertman (1968), and Paterson (1972). It appears that many
natural ice masses may be close to instability. However, these
calculations are subject to certain limitations:
(a) They are based on a theoretical model which rests on
certain assumptions that may not be valid. Moreover, the
model is a purely thermal one; ice dynamics is ignored.
(b) We have used numerical values of the flow law parameters
and creep activation energy which are subject to consider-
able uncertainty.
(c) Basal shear stress and geothermal heat flux are seldom
known precisely. Uncertainties in aB are particularly
serious because is proportional to QB
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Paterson, W. S. B.; Nitsan, U. & Clarke, G. K. C. Investigation of creep instability as a mechanism for glacier surges, article, January 1, 1976; New Mexico. (https://digital.library.unt.edu/ark:/67531/metadc1449092/m1/17/: accessed July 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.