An ancient story tells of the kamikaze, or "divine wind," that twice saved Japan from Kublai Khan's Mongol fleets. So powerful was the legend that centuries later thousands of World War II pilots known as kamikazes would sign up to protect Japan again, by crashing their planes in suicide missions.
Now University of Massachusetts Amherst geologist Jon Woodruff says he has uncovered evidence of some truth to the legend of the ancient kamikazes, typhoon-strength winds that saved Japan from Kublai Khan in the 13th century.
Woodruff traveled halfway around the world to find evidence of the winds in Japanese lake beds, near the site of shipwrecks thought to be part of Kublai Khan's sunken armada.
"This is one of the earliest historical examples of atmospheric and oceanic conditions having a significant geopolitical impact," says Woodruff. Not until the 20th century would Japan have to defend its borders from a foreign power again.
Stuff of Legend
Some details of the story are known historical fact.
In the 13th century, Genghis Khan's grandson Kublai Khan had already conquered much of China and hoped to expand his Mongolian empire. To attack Kyushu, the southernmost of the four main Japanese islands, he amassed an enormous fleet of Chinese and Korean ships. It was one of the largest armadas the world has ever seen, with more than 140,000 sailors, according to Woodruff.
Yet twice, in 1274 and 1281, Kublai sent his overwhelming forces across the Korea Strait, and twice his fleet was destroyed.
Legend has it that Khan's ships were sunk when an emperor summoned two massive storms, the kamikazes.
The problem with this story, aside from the question of whether the storms were divinely ordained, is that powerful typhoons are relatively rare today in the part of western Japan that was attacked. Historians tend to give more credit to the Japanese troops who defended their land.
Scholars also note that modern popularization of the kamikaze story, in which an emperor summons the divine winds that project Japan, has an element of propaganda to it. Emperor Hirohito resurrected the tale in the final hours of World War II, when he appealed to Japanese pilots to become his divine winds and defend their homeland by crashing into Allied forces.
Woodruff and his team excavated sediments from beneath lake bottoms near the coast that suggest typhoons were more common in western Japan half a millennium ago than they are today. Two of the sediment layers may even have been laid down by the very typhoons that inspired the kamikaze legend.
"We have fairly strong evidence of two intense inundations at the end of the 13th century," says Woodruff.
Searching for Kamikaze
Sediments buried beneath lakes give geologists a record of past weather, because they often contain materials washed in by storms. Some of the old layers Woodruff's team hauled up from beneath Lake Daija, near the coast of Kyushu, contained unusually large amounts of rock made from other ground-up rocks—called clastics—and the metal strontium. The most likely source of these materials would be massive amounts of sand and pulverized shells washed in from the beach by typhoons.
At another lake on the western edge of Kyushu, the researchers found deposits rich in clastics and titanium, a metal probably scoured from the bottom of a nearby river, also by typhoons.
And not just any typhoons. Dated carbon samples in the sediment layers associated with the two largest storms suggest they occurred at the right time to have been the legendary storms that saved Japan.
But there's enough uncertainty in those carbon dates to leave room for doubt, and Woodruff's geological records must also contend with historical accounts. A description of the first battle, in 1274 at Hakata Bay, was recorded for posterity by a samurai who makes no mention of a typhoon, only a shift in wind direction that helped the Japanese prevail.
As for the second attack in 1281, archaeologist James Delgado wouldn't be surprised if a huge typhoon was involved. He has seen the remnants of the devastated fleet firsthand, in sunken shipwrecks first discovered in Imari Bay in the 1980s.
Japanese scientists exploring the wrecks found a Chinese plaque, the remains of a Chinese soldier, and other artifacts that "powerfully proved" the sunken ships once belonged to Kublai's Mongol armada, says Delgado, who was not involved in the geology study.
"History isn't simple," says Delgado, director of maritime heritage at the National Oceanic and Atmospheric Administration's Office of National Marine Sanctuaries. "Too much of an emphasis on the storm takes away from the human elements."
Divers have also unearthed burned timbers, a clue that the typhoons got some help from soldiers in repelling the Mongol invasion. Japanese war tactics may have included sailing flaming boats into their adversary's fleet.
Next year Japanese teams expect to begin excavating a shipwreck found in 2011 for more archaeological clues. What treasures will be found within and what new wrinkles may be added to the tale of the kamikaze remain to be seen.
Correction: An earlier version of this story incorrectly named Shikoku as the island attacked by Kublai Khan. The correct island is Kyushu.