A 400 meter long crack was reported as visible along the frozen surface of Lake Suwa in Suwa, Nagano Prefecture, on Monday.
The local mythical tradition says that this crack is said to be a path used by a male god of the Suwa Taisha Kamisha shrine (on the southern bank) to meet a goddess of Suwa Taisha Shimosha shrine on the opposite shore (northern bank). (Other versions: The ice cracks are caused by the gods’ trekking across the lake to visit the various buildings of the 12th century- old Suwa Grand Shrine.)
The phenomenon, known as ”omiwatari,”御神渡り or “Passage of the gods” was confirmed officially Tuesday morning, occurred for the second straight year, but 13 days earlier than last year due to severe cold.
A priest from the Yatsurugi Shrines check the location of the ice crack and perform purification rite. They hold a Shinto ritual to foretell next year’s crop harvests and weather.
The predictions will be made at the shrine later after comparing their findings with last year’s records.
The preferred scientific explanation of today is that the “path” is caused by the continuous expansion and contraction of ice that is caused by the difference between daytime and nighttime temperatures. The lake has a natural hot spring under the surface, so that when the top freezes in the winter, the lower waters are still warm and circulating. This results in pressure ridges forming in the ice, reaching heights of 30 cm or more.
Read more below in the Japan Times news article from a year ago:
Ice phenomenon warms up hearts in the Lake Suwa region
MAR 3, 2012
To the delight of local residents this winter, an elevated line of cracked ice appeared on the frozen surface of Lake Suwa in Nagano Prefecture for the first time in four years.
The natural phenomenon is called “omiwatari,” or the god’s footsteps, with the name coming from a myth in the Suwa region.
It is traditionally interpreted as a good omen for the coming year.
However, the frequency with which the ice pattern appears has dropped since the 1990s, a trend blamed on global warming. The sharp upheaval of ice that used to appear almost every winter has become rare in recent years, eliciting feelings of gloom.
Omiwatari occurs when the ice on the lake repeatedly expands and contracts as the temperature swings between day and night.
When the pressure ridge rises 30 cm to 180 cm, Yatsurugi Shrine usually certifies it as omiwatari.
This year, however, the shrine verified the phenomenon on Feb. 4 even though the cracked ice shards had risen only about 10 cm.
“We were of two minds as to whether to certify it as omiwatari, but I felt mounting expectations from local people this year,” said shrine priest Kiyoshi Miyasaka, 61.
Yoshiaki Natori, 64, Yatsurugi Shrine’s chief representative, also remarked that he had a strong wish that this year will be peaceful and disaster-free, unlike 2011.
Unfortunately, however, the ice pattern that drew nationwide attention collapsed after it rained Feb. 6 and 7.
When there is no omiwatari on the lake because of a mild winter, locals refer to its as “akenoumi.” While akenoumi was observed only 15 times during the 63 years of the Showa Era (1926-1989), it has already occurred 17 times in the 24 years since the start of the Heisei Era in 1989.
According to Meteorological Agency records, the average temperature in the Suwa region has risen from 9.1 degrees in 1945 to 11.2 last year.
“Obviously, global warming is the cause of the falling number of omiwatari. But this winter was unusually cold. There were several days the temperature plunged to minus 13. So that might be a reason why we had it for the first time in four years,” said Tokio Okino, a professor emeritus at Shinshu University and an expert on Lake Suwa’s natural environment.
When the lake freezes, the ice protects smelt during the spawning period from attacks by birds and supports the agar business, a point of local pride.
As omiwatari is the symbol of severe cold winters, it is also played up by the local tourism industry.
“A cold winter used to be part of the natural cycle in the Suwa region. But it has been losing its balance. I am worried about how long it will be before we see the next omiwatari,” Miyasaka, the shrine priest, said.
Further readings and references:
Lake Suwa (Wikipedia)