For at least six centuries, residents along a lake in the mountains of central Japan have marked the depth of winter by celebrating the return of a natural phenomenon once revered as the trail of a wandering god.
It would only appear after days of frigid temperatures had frozen Lake Suwa into a sheet of solid white. First, people were awakened at night by a loud rumbling. Dawn broke to reveal its source: a long, narrow ridge of jagged ice that had mysteriously arisen across the lake’s surface, meandering like the spiked back of a twisting dragon.
This was the Miwatari, meaning the sacred crossing, which local belief held was left by a passing god of Japan’s native Shinto belief. Its appearance evoked feelings of awe but also reassurance among the residents, who ventured onto the ice to perform a ceremony honoring what they saw as a visitation from the supernatural. In the rare winters when the ice ridge did not appear, the god’s absence was viewed as a warning that the natural world was out of balance.
So important was the Miwatari that residents recorded whether it appeared, the condition of the lake and what historical events accompanied it. They have loyally written these descriptions every winter since 1443, creating a remarkable archive that attests to centuries of monotonously cold winters.
But recently, the chronicles of Suwa have told a different, more alarming story. For the past seven winters, the Miwatari has failed to appear because the lake didn’t freeze. While there have been occasional years without ice, an absence of this length has happened only once before in the archive, and that was a half millennium ago.
In fact, Lake Suwa has not fully frozen over — what locals call “an open sea” — for 18 of the past 25 years. Kiyoshi Miyasaka, the chief priest of Yatsurugi Shrine, which for the past three and a half centuries has borne the duty of maintaining the records, says ice has failed to appear with regularity since the 1980s. He and other locals blame the disappearance of the ancient rhythms on global climate change.
“In old times, an open sea was regarded as a bad omen,” said Mr. Miyasaka, 74, whose shrine’s traditional stone gate and tile-roofed wooden buildings stand about a mile from the lakeshore. “We hear about melting of ice caps and Himalayan glaciers, but our own lake is also trying to alert us.”
Every dawn through most of January and early February, Mr. Miyasaka and dozens of his parishioners gather at a parking lot on the lake’s edge to check if the god had passed by during the night. For years now, they have found only disappointment.
Only parishioners in their 60s or older remember when the Miwatari was still big enough to make a sound that could wake them at night. The last time an ice ridge formed, in 2018, it was barely six inches tall.
“When I was child, the ice spikes rose higher than my height,” said Isao Nakazawa, 81, a retired auto company worker. “We knew when it appeared because it made a sound like a taiko drum, ‘Gon-gon-gon!’”
These days, the Miwatari has lost much of its religious significance. Residents in Suwa, a small, sleepy city wrapped along the lake’s edge, see it as a local rite of winter. The city’s mayor joins the gatherings on cold mornings alongside the lake.
“Carrying on a tradition for 580 years binds our community together,” said the mayor, Yukari Kaneko, 66. “I fear what’s happening now is a warning to rethink how we’re living.”
Science has also robbed the ice ridges of their mystery by explaining how they arise. When Lake Suwa freezes, its surface hardens into a slab some two and a half miles across. On particularly cold nights, the ice contracts, opening cracks that fill with lake water, which also freezes. As temperatures rise again, the slab expands back into its original shape, pushing the newly formed ice upward into buckled ramparts.
Similar ice ridges appear elsewhere, including on Lake Mendota in Wisconsin. But records rarely go back so far or in such detail as in Suwa.
“This chronicle is quite special because the people have recorded the same thing in the same way for centuries,” said Dagomar Degroot, a professor of environmental history at Georgetown University. “It’s an example of a cultural heritage that is slipping away and may not come back.”
While Mr. Miyasaka says he feels discouraged by the failure of the ice ridge to return, he intends to keep updating the archive.
“You cannot just quit something that has been around for more than 580 years,” said Mr. Miyasaka, whose family has held the position of chief priest for five generations. “I will not be the one who ends it.”
His parishioners say they will continue to join him in checking the lake on winter mornings. “I feel a responsibility to keep this history going,” Hiroyuki Okazaki, a 63-year-old carpenter, said.
Neither Mr. Miyasaka nor his parishioners say they believe that they have actually been abandoned by a god — Japan has become far too secular for that. They don’t even know which god was supposed to be crossing the lake. The ancient records don’t give a name, and Shinto is a form of animism that believes in countless gods that lie behind the forces of nature.
In modern times, a tale appeared of a male god crossing the lake to visit his wife, but Mr. Miyasaka said this was the work of enterprising local business owners using romance to draw tourists. Some locals also add an extra “o” to the front of Miwatari to make the word sound more contemporary, he said.
The chief priest has read through all of the chronicle’s entries, including the oldest now stored in a museum. Most of the pages, written with brushes and ink and bound in hand-sewn books, tell of the Miwatari appearing with comforting regularity. During the entire 17th century, the ice ridge failed to appear only twice.
In 1986, his father taught him how to perform the ceremony to honor the Miwatari’s appearance, in which he led parishioners onto the frozen lake and waved a holly branch as the ice creaked beneath their feet. At the time, Mr. Miyasaka assumed he would have to do this every year.
Instead, he’s led the ceremony only nine times since then.
“When our ancestors made these records centuries ago, they never imagined they would tell such a story,” Mr. Miyasaka said. “They have become a warning of global warming.”
