Ancient Jomon Pottery Unearthed at Lake Biwako Underwater Ruins
A nearly complete pottery vessel, estimated to be over 10,000 years old, was discovered near the Tsuzuraozaki underwater ruins in Lake Biwako, Shiga Prefecture, according to officials on November 25.
The vessel, approximately 25 centimeters tall with a pointed base, was recovered from a depth of 64 meters. Based on its form and engraved patterns, researchers identified it as either Jinguji-style or Konami Upper-layer style pottery. Dating estimates place it between 11,000 and 10,500 years ago, representing the early phase of the Jomon Pottery Culture Period (14500 B.C.–1000 B.C.) and making it the oldest artifact discovered at this site.
The survey was commissioned by the Nara National Research Institute for Cultural Properties and conducted in collaboration with Shiga Prefecture and other organizations. Researchers used an advanced underwater scanner to generate a 3D map of the lakebed in October.
“This survey collected data comparable to what human divers could achieve, even at such deep-water sites,” said Yoshifumi Ikeda, a professor of underwater archaeology at Kokugakuin University. The team utilized a system originally designed for submarine cable inspections, employing four cameras to visualize the terrain and artifacts in waters exceeding 30 meters depths that are challenging for divers.
The survey area extended 200 meters east to west and 40 meters north to south, located 30 to 50 meters south of the previously known ruins. Video footage also revealed six Haji pottery jars, about 1,500 years old from the Kofun Period (3rd–7th centuries AD), arranged within a 144-square-meter area near the newly discovered vessel. The two finds are separated by more than 8,000 years in age.
Because artifacts recovered from land sites are often damaged, nearly intact pottery is more likely to survive underwater, though such excavations have historically been difficult. This new method promises to improve research on submerged sites nationwide.
“Without relying on large submersibles, we can make significant progress in underwater archaeology, especially in calm inland seas and lakes,” Ikeda said. Japan has nearly 400 underwater archaeological sites. The Tsuzuraozaki site was first identified in 1924 when Jomon pottery appeared in bottom trawl nets. Since then, about 200 pottery fragments from the Jomon to Heian periods (794–1185) have been recovered, but the full extent of the ruins remains unknown.
The site’s origins are still debated, with theories ranging from pottery washing in from nearby land, ritual or funerary use, abandonment, land subsidence due to earthquakes, or shipwrecks none of which has been confirmed.
Advantages of Underwater Preservation
Kenichi Yano, a professor of archaeology at Ritsumeikan University, noted the significance of the discovery: “It is nearly impossible for 10,000-year-old pottery to remain intact on land. This find highlights the unique benefits of underwater archaeology.”
He added that locating the vessel in its original lakebed position is particularly meaningful, as many prior finds were recovered from trawl nets. The site lies within a valley-like depression at depths over 80 meters. Continuous subsidence due to tectonic activity, along with minimal sediment accumulation in the valley, likely allowed the artifacts to remain exposed for millennia.
“The new discovery will enhance our understanding of the site’s origins and the geological features of the surrounding area,” Yano concluded.
