Iceberg Deterioration 

 Discussion and 

 Conclusions 



Of the four physical processes 

 used in the IIP nx)del to predict 

 deterioration, wave erosion is 

 responsible for the vast majority 

 of the predicted erosion. This 

 equation is dependent on SST, 

 wave height, and period. (Calving 

 of growlers from an iceberg is not 

 directly modelled but is 

 dependent on wave erosion.) 

 The SST and wave heights 

 experienced by the three 

 icebergs observed in 1 985 were 

 not significantly different. 



The amount of wave-induced 

 erosion of an iceberg of a given 

 length under the same 

 environmental conditions is 

 dependent on the shape of the 

 iceberg and the amount of 

 surface area exposed to wave 

 action. The shape of an opening, 

 large or small, in an iceberg can 

 cofKentrate the wave energy on 

 a small area creating faster 

 erosion and subsequent calving. 

 If an iceberg has a large exposed 

 waterline-to-mass ratb, as did 

 icebergs #2 and #3, wave erosion 

 with associated calving is a more 

 effective deterioration force than 

 on an iceberg (like iceberg #1) 

 with a relatively small exposed 

 waterline-to-mass ratio. 



The model-predicted 

 deteriorations for icebergs #2 and 

 #3 were less than the observed 

 rate over the entire observation 

 period. The instances where the 

 observed icebergs deteriorated 

 much more rapidly than predicted 

 by the model are correlated with 

 observed calving events and no 

 associated rollover or rise of the 

 iceberg ( Figure C-5). The model- 



predicted deterioration for 

 iceberg #1 was greater than that 

 observed over the entire 

 obsen/ation period. Iceberg #1 

 had no observed major calving 

 events. The major reason for the 

 model's poor perfonnance with 

 iceberg #1 was the increase in 

 maximum length due to rollover. 

 Before the iceberg rolled over, 

 the rrxjdel-predicted deterioration 

 ctosely matched the observed 

 deterioration, and after it 

 stabilized on day 4, the observed 

 deterioration again closely 

 matched the model-predicted 

 deterioration. 



Under operational conditions, the 

 required environmental data for 

 the deterioration model are 

 supplied by FNOC. On their own, 

 the observed errors in the wave 

 height data would increase the 

 modelled deterioration rate 

 significantly. Part of this increase 

 is, however, offset by the 

 increased period of the bigger 

 waves. (Wave height is in 

 numerator while wave period is in 

 the denominator of the wave 

 erosion equatbn (Anderson, 

 1 983).) During the largest error in 

 FNOC wave height (17 feet), the 

 deterioration rate would have 

 been increased by about 25 

 percent. 



Given accurate environmental 

 data, the iceberg predictbn 

 model used by IIP predicts the 

 deterioration reasonably well. 

 Because of errors introduced by 

 our present methods of operation 

 (FNOC data errors and SLAR 

 sizing errors), IIP will continue its 

 conservative approach and will 



require that an iceberg 

 deteriorate! 75% of its original 

 length before it is eliminated. 

 Future IIP cmises will continue to 

 gather iceberg drift and 

 deterioration data to further 

 evaluate the performance of the 

 models. 



References 



Anderson, I. (1983); Iceberg 

 Deterioration Model, Appendix C 

 of the Report of the International 

 Ice Patrol Service in the North 

 Atlantic. Bulletin No. 69., CG- 

 188-38, Intemational Ice Patrol, 

 Avery R.,Groton,CT 06340- 

 6096 



Anderson, 1.(1984); 

 Oceanographic Conditbns on 

 the Grand Banl<s During the 1984 

 International Ice Patrol Season, 

 Appendix B of the Report of the 

 International Ice Patrol Sen/ice in 

 the North Atlantic. Bulletin No. 

 70., CG- 188-39. International Ice 

 Patrol. Avery R., Groton. CT 

 06340-6096. 



White, F. M., M. L. Spaulding, and 

 L.Gominho(1980); Theoretical 

 Estimates of the Various 

 Mechanisms Involved in Iceberg 

 Deterioration in the Open Ocean 

 Environment, U. S. Coast Guard 

 Research and Development 

 Center Report CG-D-62-80, 

 126pp. 



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