HR: 0830h
AN: C11D-0858    [PDF]
TI: Log-periodic oscillations in the acceleration phase prior to break-off of a large ice mass.
AU: Funk, M
EM: funk@vaw.baug.ethz.ch
AF: Versuchsanstalt fur Wasserbau, Hydrologie und Glaziologie, VAW, Gloriastrasse 37-39 ETH Zentrum, Zurich, 8092 Switzerland
AU: * L\"uthi, M P
EM: luthi@gi.alaska.edu
AF: Versuchsanstalt fur Wasserbau, Hydrologie und Glaziologie, VAW, Gloriastrasse 37-39 ETH Zentrum, Zurich, 8092 Switzerland
AU: * L\"uthi, M P
EM: luthi@gi.alaska.edu
AF: Geophysical Institute, Universtiy of Alaska Fairbanks 903 Koyukuk Dr PO Box 757320, Fairbanks, AK 99775 United States
AU: Pralong, A
EM: pralong@vaw.baug.ethz.ch
AF: Versuchsanstalt fur Wasserbau, Hydrologie und Glaziologie, VAW, Gloriastrasse 37-39 ETH Zentrum, Zurich, 8092 Switzerland
AB: Large ice masses do not break off hanging glaciers without prior characteristic changes in appearance and movement. Formation of deep crevasses, and cracked ice near the glacier base are indications of a pending breakoff event. An empirical power-law fit is routinely used to predict the time of failure. The recognition and assessment of ice avalanche hazards from hanging glaciers largely relies on these facts. Several remarkable properties of the acceleration phase prior to failure can be described with a model system based on damage mechanics. The empirical formula used to predict failure time is obtained, which allows a physical interpretation of the empirical parameters. The solution reveals that two parameters of the empirical formula are related. This considerably reduces the complexity of predicting the time of failure. Characteristic length and time scales seem to be universal quantities of the failure process in hanging glaciers. The numerical values $t_f$= 550 days and $s_f$=55 m are obtained by analyzing survey data from 15 break-off events. Measured ice velocities prior to break-off exhibit oscillations which can be described as log-periodic corrections to the leading velocity singularity. The exact cause for these oscillations is still unclear, but dynamical crack interactions or damage reduction due to healing are likely explanation.
UR: http://gi.alaska.edu/\textasciitilde{}luthi/
DE: 1827 Glaciology (1863)
DE: 8010 Fractures and faults
SC: Cryosphere [C]
MN: 2003 Fall Meeting