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A Study of Several Pressure Ridges and Ice Islands in the Canadian Beaufort Sea

Published online by Cambridge University Press:  30 January 2017

J. Hnatiuk ,
A. Kovacs  and
M. Mellor
J. Hnatiuk
Affiliation:
Gulf Oil Canada Ltd., P.O. Box 130, Calgary, Alberta T2P 2H7, Canada
A. Kovacs
Affiliation:
Gulf Oil Canada Ltd., P.O. Box 130, Calgary, Alberta T2P 2H7, Canada
M. Mellor
Affiliation:
U.S. Army Cold Regions Research and Engineering Laboratory, Hanover, New Hampshire 03755, U.S.A.
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Abstract

The environment conditions in the southern Beaufort Sea are described with special emphasis on pressure ridges and ice islands. Techniques for determining the geometric configurations and the physical and mechanical properties of sea-ice structures and ice islands are described. Profiles of pressure ridges were determined by surface surveys, drill-hole probes and side-looking sonar scanning. Multi-year pressure ridges with thicknesses up to 18 m and widths up to 110 m were examined in detail. The first-year ridge of 22 m thickness and 100 m width was studied. Results are given for several multi-year ridges and the first-year ridge. Information obtained from dives under the ice is also given. Corresponding data are given for grounded ice islands with particular attention being given to contact between the ice and sea bed. A 19 m thick ice-island fragment grounded in 13 m of water was one of several investigated. Measurements of temperature, salinity, tensile strength and compressive strength are given for ice taken from old pressure ridges and factors influencing the interpretation of test data are discussed. The data obtained in this study will be used in engineering design studies for off-shore structures for drilling and production of hydrocarbons from the Beaufort Sea area. Exploratory drilling in shallow water has already been carried out and off-shore drilling from drill ships is scheduled to commence in the study area during the open-water season of 1976.

This paper will be published in full in a future issue of Journal of Glaciology.

Type
Abstract
Information
Journal of Glaciology , Volume 19 , Issue 81 , 1977 , pp. 666 - 667
Copyright
Copyright © International Glaciological Society 1977

Discussion

E. Kopaygorodskiy: Have you studied the mechanical properties of the sail and the keel?

J. Hnatiuk: We realize that the mechanical properties of pressure-ridge ice are important and performed some Brazil, compressive and tensile strength tests. The results were rather lower than expected, probably because of difficulties with specimen preparation. One can also infer the ice strength from a knowledge of its brine concentration and temperature.

Kopaygorodskiy: How does the load imposed on a structure by a pressure ridge compare with that due to a smooth sheet of ice?

Hnatiuk: The loads imposed will certainly be higher than for sheet ice, but have not been measured by us. Some measurements on thinner ridges have been made by Imperial Oil.

W. F. Weeks: Most parts of multi-year ridge ice behave like cold, low-salinity ice. We might consider sea ice to be a composite of this ridge ice and thinner sheet ice in evaluating its mechanical properties and the loading effect on structures.

Kopaygorodskiy: Were any attempts made to develop a laboratory model of pressure ridges?

Hnatiuk: We have certainly considered a model, but this has not yet been done.

D. Bruce: Could you comment on the soil characteristics at the location of the deep ice scour?

Hnatiuk: In the Mackenzie Delta this is clay or silty clay. Further north the soil is more sandy.

H. Fangel: Can any indication be given of the age of grounded ice islands in the Beaufort Sea?

Hnatiuk: The fact that the thickness has decreased from about 55 m on calving at Ellesmere Island to about 25 m on grounding may give some clue. A substantial calving in the mid 60s resulted in several fragments being grounded on the Alaska coast in 1972. Perhaps our fragments are of a similar age.

S. F. Ackley: Were your island fragments observed to remain throughout the summer, or were they carried away during the ice-free period?

Hnatiuk: Our fragments all moved out the next season, though some stayed till close to the end of the summer.