NRC Publications Archive Archives des publications du CNRC Ice behaviour around a small Arctic island Frederking, R. M. W.; Sanderson, T.; Wessels, E.; Inoue, M. This publication could be one of several versions: author’s original, accepted manuscript or the publisher’s version. / La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version acceptée du manuscrit ou la version de l’éditeur. Publisher’s version / Version de l'éditeur: The Seventh International Conference on Port and Ocean Engineering under Arctic Conditions. POAC 83, 2, pp. 875-887, 1983 NRC Publications Archive Record / Notice des Archives des publications du CNRC : https://nrc-publications.canada.ca/eng/view/object/?id=c38b446c-8d3d-49ba-9e57-5e0dbb0e054f https://publications-cnrc.canada.ca/fra/voir/objet/?id=c38b446c-8d3d-49ba-9e57-5e0dbb0e054f Access and use of this website and the material on it are subject to the Terms and Conditions set forth at https://nrc-publications.canada.ca/eng/copyright READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE. L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site https://publications-cnrc.canada.ca/fra/droits LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB. Questions? Contact the NRC Publications Archive team at [email protected]. If you wish to email the authors directly, please see the first page of the publication for their contact information. Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à [email protected]. TH1 N21d National Research Conseil national no* Council Canada de recherches Canada c. 2 BLDG ICE REHAVIOUR AROUND A SMALL ARCTIC ISLAND by R. Frederking, T. Sanderson, E. Wessels and M. lnoue Appeared in VTT Symposium 28 The Seventh International Conference on Port and Ocean Engineering under Arctic Conditions Helsinki, Finland, 5 - 9 April, 1983 Volume 2, p. 875 - 887 Reprinted with permission Technical Research Centre of Finland (VTT) , . p2-i- ! I DBR Paper No. 1149 i3:T,. , .- --. , . , .t--*- 1 Division of Building Research ?.,-,.i ,, I;;-:- I -;l,,b;, TJ . - - >.--.-.-,I-,- Price $1.25 OTTAWA NRCC 22804 R. Frederking, Division of Building Research, National Research Council of Canada, Ottawa. Canada KIA 0R6. T. Sanderson, BP Petroleum Development (Overseas) Ltd. London ECZY 9BU. England. E. Wessels, Hamburgische Schiffbau-Versuchsanstalt (HSVA), Hamburg. West Germany. M. Inoue, Nippon Kokan K.K., Japan. (Visiting scientist at DBR, NRC .) ICE BEHAVIOUR AROUND A SMALL ARCTIC ISLAND Abstract Adams Island, 200 m in diameter and about 3 km offshore in Lancaster Sound, has been established as a site for studying ice interaction processes. Preliminary surveys of ice and environmental conditions over the winter 1981/82 shoved ice features reflecting a short-term pile-up as well as long-term thrust on the island. Associated ice pressures were in the range 40-400 Wa. Information on first-year ice cover, icebergs and multi-year floes was also collected. 1. INTRODUCTION A small island can be taken as representative of a man-made offshore structure. Observations of ice interactions with the island are relevant to predicting ice forces on structures. provided there are suitable ice conditions and movements. This approach was used in an investigation of impact of large multi- year floes on Hans Island /6/. Similar studies have been made of first-year sea ice rubble formations at Fairway Rock /5/. Adams Island, about 200 m in diameter, is located at the intersection of Lancaster Sound and Navy Board Inlet in the Canadian Arctic. Ice conditions in the area include level first-year sea ice, pressure ridges, multi-year ice, pack ice and icebergs. Both dynamic and land-fast ice conditions prevail over the course of the winter. A joint project, to extend over three winter seasons, with participants from several countries, was initiated to observe and measure ice interaction processes and environmental driving forces around Adams Island in order to characterize the processes and develcp analytical models for predicting ice forces. Over the winter 1981182, periodic site visits, including several by a contractor and a 2-week major field visit in March, were made to survey ice and environmental conditions. A more extensive presentation of these results appears elsewhere 131. 2. SITE DESCRIPTION The area of investigation is at the intersection of Lancaster Sound and Navy Board Inlet (Fig. 1). Lancaster Sound, the FIGURE 1 LOCATION MAP FOR ADAMS ISLAND AREA eastern entrance to the Northwest Passage, extends to the west from Baffin Bay into the islands of the Canadian Arctic. Ice moves generally eastward through Lancaster Sound, under the action of wind and current. Navy Board Inlet is a fiord-like feature which connects through Eclipse Sound and Pond Inlet to Baffin Bay. Water depth in Lancaster Sound reaches 800 m, and 400 m in Navy Board Inlet. A sill at their intersection does not exceed 200 m in depth and for the most part is less than 100 m deep. The tidal range is about 1.5 m. Adams Island is situated about 3 km offshore from the Borden Peninsula (Fig. 1 insert). Borden Station, with accomodatioa buildings and a 300 m air-strip, provided a base for operations in the area. A detailed map of the island and local bathymetry are shown in Fig. 2. The island is rocky, with steep cliffs on Fig. 2 Adams Island sharing profiled features, ice movements and bathymetry (water depth in m) 0 SHORI-TERM ICE MOVEMENT LlARKERS LOhG-ICRM ICf MOVChlENT SIIRVEY POLES IlOliEhlLNI SCALE m i- > h!AD SCALE m 0 I92 IOC the north side. Maxinum elevation (20 m) is on the northern side, with gradual slopes to the east, south and west. The south shore is also nearvertical, with an escarpment about 4 m high. The beaches are rocky and relatively steep 171. There is no possibility of landing even a small boat on the island, except on a mobile spit on the southwest corner. As can be seen in Pig. 2, the slope of the sea bottom is gradual to the north and west. The steepest submarine slope is to the southeast. The sea bottom is very rocby. For a normal season, ice first forms in the middle of Navy Board Inlet in October. This ice becomes land-fast and progresses up the inlet, reaching Lancaster Sound in December. The island is generally at the boundary between level and ridged ice. Shear and pressure ridges form a zone of ridged ice which becomes land- fast in mid-winter to about 2 Ian north of the island. During the open water season, multi-year ice from the Arctic Archipelago moves through Lancaster Sound to be discharged into Baffin Bay. Similarly, icebergs from the glaciers of Greenland and Ellesmere Island circulate in the Sound. Some of these bergs pass into Navy Board Inlet and are frozen into the ice cover while others ground on the sill at the entrance to the inlet. Typically there can be 5 to 10 large icebergs within 10 km of Adam Island. Multi-year ice is also frozen into the ice cover and may reach - coverages of 1 to 5%. The pack in Lancaster Sound is generally dynamic throughout the entire winter although on occasion it has been reported as completely land-fast and static /I/. 3. ICE PROFILES Ice interactions in the immediate vicinity of Adams Island were characterized by measuring vertical profiles along several lines extending out from the island. The results of two representative lines, one to the southwest believed to represent a long term thrust (buckle) feature, and the other to the southeast representing a pile-up (Fig. 2 gives locations) are presented in - 879 - Pigs. 3 and 4 respectively. The profiles were constructed from measurements of surface elevation, ice thickness, snov depth and water depth at 4 m intervals. These measurements were made during the March field visit. 3.1 Long term thrust (buckle) feature The profile illustrated in Fig. 3 is typical of a feature which extended for about 150 m along the southwest side of the island, roughly parallel to the shore. The ice thickness in this feature (2-3 m) is greater than the adjacent level ice (1.3 m). This is -f 5 TIDAL - - .I MEASURED POINTS //5 SNOW WXY ROCK --la FIGURE 3 PROFILE OF SOUIHWEST ICE FEATURE AOAMS ISLAND MARCH 1982 most likely due to water flooding onto the surface at high tide and subsequently freezing. Tidal flooding was observed during the course of the two-week field visit. Tidal cracks were also noted and seen to change, some becoming inoperative and new ones forming. A similar tidal-related thickened ice zone has been observed in Strathcona Sound around a wharf 121. The near-vertical ice feature at 20 m was produced by a progressive tilting up of the ice cover. This rotation is shown by the curved arrow in Fig. 3. Further evidence was a set of snowmobile tracks, clearly visible on this nearvertical surf ace; they had been made during a February reconnaissance to the island. At some positions along the feature the tilt-up was not as great and in other cases the rotation was more than 90'. As yet there is no definite explanation for this tilting. It is most likely due to the combined effects of buckling, resulting from horizontal movement of the ice cover towards the island, and tidal cycling.