Abstract
A thermal ice ridge is a height upheaval of ice, like a dragonʼs dorsal fin, along cracks in a frozen lake (Figure 1). Omiwatari (or Godʼs Crossing), or thermal ice ridges, were considered to result from an increase in ice temperature leading to thermal expansion of the ice plates. However, Hamaguchi (2009) recently collected data on Lake Suwa (36° 03'N, 138° 05'E) from the perspective of volcano physics and seismology and proposed a new theory (based on a volume increase at the phase change from water to ice) stating that the ridges form when the air temperature drops, thus reversing the traditional theory. In this study, we use quantitative observation and thermal ice ridge outbreak pictures captured by a video camera with a crack width of the thermal ice ridge of Lake Kussharo (43° 37'N, 144° 20'E) and inspection through more recent observations at the actual site. Our results reveal that new ice was generated on an open surface of water due to shrinkage of the ice plate cooled at night, and a thermal ice ridge occurred from expansion of the ice plate when the ice temperature rose during the daytime. In addition, although the conventional study focused only on generation of thermal ice ridges, this report aims to acquire an observational record of later development of thermal ice ridges after generation, successfully clarifying a basic process of such development of thermal ice ridges.
