Topography of Sea Ice Sheets

Figure 1-35.—Sizes of sea ice. Topography of Sea Ice Sheets In addition to separating pieces of sea ice from the fast ice by pulling it apart, the winds and currents may also push on fast-ice sheets, causing stress budges or stress ruptures in the surface with portions of the sheet overriding other sections. Many of these stress-induced features are identified by specific terms that describe the topography, or configuration of the ice surface. These terms are related to the degree of ice-surface roughness. Figure 1-36 illustrates the types of topography. RAFTED ICE.—This type of topography occurs when ice cakes override one another. Rafting occurs when wind forces ice cracks or ice floes together. It is associated with young and first-year ice. When the rafting process is occurring, there is great compression within the ice sheet. Ships should avoid operations in any opening in the ice in an area where rafting is occurring, because it indicates the ice is closing in rapidly. RIDGED ICE.—Ridged ice is much rougher than rafted ice and occurs with first-year ice. Wind and weather eventually smooth the surface of the ridges. HUMMOCKED ICE.—Hummocking occurs with old ice. It is defined as ice piled haphazardly into mounds or hillocks. At the time of its formation, hummocked ice is similar to rafted ice; the major difference is that hummocked ice, because of its thickness, requires a greater degree of pressure and heaping. 1-52