Pressure ridges and hummocks, which are the largest of the ice relief features, present formidable problems to design of off-shore facilities and to the operation of surface and subsurface shipping. The mechanics of ridge and hummock formation are reviewed and it is shown that several distinct types of ice formation features occur depending upon whether the formation mechanism is marginal crushing, overthrusting or shearing. Between 1969 and the present a number of both free-floating and grounded ridges have been examined by the authors in the Bering, Chukchi and Beaufort Seas. Profiles of the upper and lower surfaces of the ridges were determined by leveling and by drilling and sonar, respectively, and the internal structure of the ridges was investigated by coring. Ice temperatures, salinities, and densities were obtained and brine volumes were computed from the temperatures and salinities. Representative profiles are presented. The present results of this program are: 1. The degree of bonding between ice blocks and, therefore, the overall structural integrity of ridge keels would appear to be variable, presumably changing with the age of the ridge and the initial temperature of the ice being incorporated into the ridge. It can be shown that during the winter the cold reserve of ice blocks being incorporated into a ridge can be sufficient to cause significant inter-block ice growth. 2. Lack of local isostatic adjustment is common in ridges. In new ridges a significant portion of the surface load is supported by the surrounding plate ice resulting in its deflection. When ridges form by thrusting, their upper and lower portions may be laterally separated by tens of meters. This obviously results in a nonisostatic condition which is compensated by deflections of the local plate ice. 3. A representative salinity for the ice in the ridges we examined was 4 percent. Temperature profiles were reasonably linear except in the lower parts of ridges with pronounced keels where temperatures were roughly constant at near freezing values. The brine volume of the ice blocks in the keels varied between 40 and 120 percent. 4. Present information indicates that the average slope angle of the above-water portion of a ridge (24 degrees) is less than that of the underwater portion (33 degrees). 5. Ridges act as effective snow fences, causing large amounts of snow to accumulate both in and around their upper parts. 6. It appears doubtful that the cross-section profiles of all ridges can adequately be represented by any one geometric model. Current data bearing on the general distribution of deformation features in time and space over the Arctic Ocean are also summarized. The data sources include the Birdseye flights, recent special laser profilometer flights, and sonar traces of the lower ice surface. Prime attention is paid to the ridging characteristics in the Coastal and Offshore Sea Ice Provinces where the ice is clearly more highly deformed than the ice in the Central Arctic Basin Province. Winter and summer distributions of both sail heights and keel depths as well as the number of ridges per nautical mile are presented.

  • Supplemental Notes:
    • Abstract of paper delivered at the First International Conference on "Port and Ocean Engineering under Arctic Conditions" held at Trondheim, Norway, August 23-30, 1971
  • Corporate Authors:

    POAC Conference

  • Authors:
    • Weeks, W F
    • Kovacs, A
    • Hibler, W D
  • Publication Date: 1971

Subject/Index Terms

Filing Info

  • Accession Number: 00025698
  • Record Type: Publication
  • Source Agency: Arctic Institute of North America
  • Files: TRIS
  • Created Date: Mar 28 1972 12:00AM