The Flexural Response of a Tabular Ice Island to Ocean Swell

Abstract

Measurements of surface strain and vertical heave responses to swell were made on a tabular ice island in Kong Oscars Fjord, east Greenland, in September 1978 . At two sites surface strain was measured with a wire strainmeter of 2 m gauge length, and heave was measured with a vertical accelerometer. While the first site was occupied a simultaneous measurement of ambient wave energy was made wit h a wave buoy. The results show that the ice island flexes and heaves in response to the longest component only of the forcing wave field, at periods above 16 s, and wit h a mean strain amplitude of the order of S x 10-7 • The results are compared with theoretical calculations of the response of a thick floating beam. In the light of the theory, t h e flexural behaviour of tabular icebergs and seaice floes is considered and their critical size ranges in relation to sea state are estimated.

Hydraulic falls under a floating ice plate due to submerged obstructions

“…Failure of the ice occurs as a result of cracks propagating through the ice. In the ocean, Goodman, Wadhams & Squire (1980) calculated that a crack would propagate if the strain reached the critical value cr = 4.3 × 10 −5 . In pure ice, however, the yield strain is higher as salt does not creep into the cracks, so cr = 2.14 × 10 −4 in this case (see Goodman et al 1980).…”

“…In the ocean, Goodman, Wadhams & Squire (1980) calculated that a crack would propagate if the strain reached the critical value cr = 4.3 × 10 −5 . In pure ice, however, the yield strain is higher as salt does not creep into the cracks, so cr = 2.14 × 10 −4 in this case (see Goodman et al 1980). The solutions presented here with the steepest hydraulic falls have the largest values of the strain, of the order of 10 −3 , and would thus be expected to fracture.…”

Melting and fragmentation laws from the evolution of two large southern ocean icebergs

“…These values are all close to the -3/2 slope already presented by (Tournadre et al, 2016) for icebergs from 0.1 to 10000 km2. A -3/2 slope has been shown both experimentally 35 and theoretically to be representative of brittle fragmentation (Astrom, 2006;Spahn et al, 2014).…”

“…It has been suggested that swell induced vibrations in the frequency range of the iceberg bobbing on water could cause fatigue and fracture at weak spots (Wadhams et al, 1983;Goodman et al, 1980). Small initial cracks within the iceberg are likely to propagate in each oscillation until they become unstable resulting in the iceberg fracture (Goodman et al, 1980).…”

“…It has been suggested that swell induced vibrations in the frequency range of the iceberg bobbing on water could cause fatigue and fracture at weak spots (Wadhams et al, 1983;Goodman et al, 1980). Small initial cracks within the iceberg are likely to propagate in each oscillation until they become unstable resulting in the iceberg fracture (Goodman et al, 1980). Jansen et al (2005) suggested from model simulations that increasing ocean temperatures along the iceberg drift and enhanced melting cause a rapid ablation 25 of the warmer basal ice layers while the iceberg core cold temperature remains relatively constant and cold.…”