• Omiwatari appeared in this winter !

    Takehiko Mikami

    A couple of straight lines of sharp upheaval of ice, called Omiwatari on the frozen surface of Lake Suwa in central Japan, appeared for the first time in 5 years on February 2, 2018. This is a follow-up report of my column on December 27, 2017.

    Snow-covered frozen Lake Suwa viewing from “Tateishi” Park (Photo taken by T.Mikami on 4 February, 2018)


    In this winter, we have a very cold weather here in Japan, and Omiwatari phenomena occurred after almost complete freezing of the lake. Daily mean temperature at Suwa observatory in this January was -1.3 degrees, which is around same as normal means. Also the number of days with lowest temperatures below -10 degrees, which is indispensable for Omiwatari occurrence, was omly two days.


    Omiwatari crossing  on Lake Suwa (Photo taken at Akasunazaki by T.Mikami on 4 February, 2018)


    Omiwatari crossing  on Lake Suwa (Photo taken at Takagi by T.Mikami on 4 February, 2018)


    According to legend, Omiwatari is said to be the footprints of God “Takeminakata-no-kami” of the Upper Suwa Shrine, who walks on the frozen lake to visit Goddess “Yasakatome-no-kami” of the Lower Shrine. The routes of Omiwatari would be different in either case due to the changes in temperature and thickness of lake ice.

    Omiwatari viewing ceremony was held by “Yatsurugi” Shinto shrine priests on 5th February, and harvests and economy in this year were predicted by referring to the past documentary data for Omiwatari crossing routes.

    Additional Information

    The range of Omiwatari was further pushed up due to the subsequent cold weather conditions at Suwa, where daily minimum temperatures dropped down to -10.9 degrees on 8 February and -11.3 degrees on 9 February.

    Omiwatari crossing  on Lake Suwa (Photo taken at Akasunazaki by T.Mikami on 10 February, 2018)

  • Omiwatari at Lake Suwa

    Takehiko Mikami

    Continuous records of lake-freezing dates since the 15th century come from central Japan, where a small lake is known for a mysterious winter phenomenon.

    Ice-cracking phenomena known as Omiwatari at Lake Suwa. Photos were taken by T.Mikami on 31 January 1998

    Lake Suwa is a small lake located in central Japan, and is known for its mysterious phenomenon called Omiwatari in the winter season. We made an attempt at reconstructing winter temperatures based on the Lake Suwa freezing record. When the lake froze, shrinkage and expansion of the ice due to diurnal tem-perature variations caused an ice-cracking phenomenon Omiwatari, which was said to resemble ‘a bridge crossing the lake. The ancient village people might have believed it to be the track of a god visiting a goddess on the opposite shore. Since the fifteenth century, the formation of Omiwatari has been celebrated in a ceremony a couple of days after its occurrence.

    Source: Hidetoshi Arakawa(1954):Fujiwara on five centuries of freezing dates of Lake Suwa in the central Japan. Archiv fur Meteorologie, Geophysik und Bioklimatologie, Series B 6 (1954): 153, table 2.

    Year-to-year variations in December-January temperatures at Lake Suwa, 1444-1870 (reconstructed) and 1891-2010(observed). Thick blue lines indicate 11-year running means.

    Source: T.Mikami, M.Zaiki and J.Hirano (2015): A history of climate change in Japan. In B.L.Batten and P.C.Brown Ed. ”Environment and Society in the Japanese Islands – From Prehistory to the Present” , Oregon State University Press.

    The dates of complete freezing and Omiwatari have been recorded by the Suwa shrine since the fifteenth century, and also by the Suwa Meteorological Observatory independently since 1951. During a cold winter, Omiwatari would already have occurred by mid-December, whereas in a warm winter, it would be delayed until the end of February, or no Omiwatari would have occurred at all. 

    In recent years, occurrence frequency of Omiwatari phenomena has been decreasing rapidly, probably due to the global warming.  There may be a possibility of rare opportunity to cerebrate Omiwatari phenomena at Lake Suwa in future.