Author(s): Jukka Tuhkuri
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Abstract: Ridges are important features of the northern seas. Ridges are elongated accumulations of broken sea ice and form when ice is deforming and fracturing due to forces from winds and currents. Rafting is another form of deformed ice. During rafting, one ice sheet overrides another ice sheet. Several models of ridging and rafting have been proposed. The early models were considering the energy needed in ridge formation. Moving ice floes have kinetic energy, that during ridge formation partly transforms into potential energy and partly is lost through friction and other phenomena. Following the important work by Parmerter and Coon (1972), the research on ridging has concentrated on understanding the kinematics of ridge formation. In this approach, the goal is to model the failure process of ice into discrete blocks, and the formation of ridges from these ice blocks. The recent work includes discrete computer simulations and laboratory experiments to identify the physical processes active during ridging. Two main variants of ridging can be identified. When compressed, thin lead ice between two thicker floes will form a ridge at the edge of a floe. This kind of ridging process is typical to the Arctic Ocean. Another kind of ridging process occurs when two ice sheets of similar thickness are compressed together. This is more typical to marginal seas, like the Baltic Sea. Work on the latter type of ridging has suggested that ridging initiates as rafting. Therefore, rafting and ridging should not be considered as two totally different deformation processes, but rather different stages of one process. This is the summary of a chapter published in Cold Regions Science and Marine Technology, a volume in the e-encyclopedia, Encyclopedia of Life Support Systems (EOLSS). EOLSS http: //www. eolss. net/ is produced under UNESCO. The editing of this volume has been an activity of the Ice Committee of the International Association of Hydro-environmental Research and Engineering (IAHR).
Year: 2014