The cause of the breakup of fast ice on March 18, 1980 near Syowa Station, East Antarctica

概要

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The complete breakup of the fast ice around Ongul Islands occurred on March 18,1980. This rare event gave rise to the disaster of the loss of two airplanes moored on ice near Syowa Station. The breakup is caused by the action of swell originating from a wind-blown open sea under a strong depression. The necessary wave height for the breakup of ice plates into pieces less than 100m length is computed from a theory based on the concept that fracture takes place when an ice plate suffers a critical strain in bending by the passage of swell under it. The critical strain is defined as the strain at which a crack of certain length at the bottom of an ice plate begin to propagate and it can be determined by both the experimentally obtained material constant K_<1c> (fracture toughness of sea ice) and the dimension of a crack. The computed wave height necessary to break an ice plate 1m thick under 12s wave period is approximately 40cm and this coincides well with observed wave height in the tide-gauge record at Syowa Station on the day of the event. Wave analyses carried out from meteorological data obtained at Syowa Station and by satellite imagery indicate that the swell damped a little on the open sea but very much in ice-covered sea as the wave height decreased from several meters to several tens of centimeter after traveling 10 or 20km.
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