IWANUMA, Miyagi Prefecture--Sand layers near an archaeological site in northern Japan provide clear evidence of three tsunami, one dating back more than 1,000 years.
IWANUMA, Miyagi Prefecture--Sand layers near an archaeological site in northern Japan provide clear evidence of three tsunami, one dating back more than 1,000 years.
According to researchers, the tsunami deposits close to the Takaose remains in the Shimonogo district here are the first geological sample showing three natural disasters that devastated the region in different periods.
The most recent layer was put down by the Great East Japan Earthquake and tsunami that struck in 2011. The other two tsunami were believed caused by the magnitude-8.1 Keicho Sanriku earthquake in 1611 and the Jogan earthquake in 869, which had an estimated magnitude of between 8.3 and 8.4.
City officials are considering whether the geological layers can be preserved and exhibited as teaching materials about the power of tsunami.
The deposits, which opened for public viewing on Nov. 10, are located about one kilometer inland. The area is where water-rice cultivation was carried out until it was submerged by several meters of seawater during the tsunami of March 11, 2011.
The excavation and research work was done on this area, which is close to the Takaose remains of the Heian Period (794-1185), as part of the city’s reconstruction projects.
According to a member of the research team, the top layer is about 20 centimeters thick with sand and mud brought by the 2011 tsunami. The boundary with the lower layer can be clearly defined as the tsunami abraded the soil and made it uneven.
Twenty-five centimeters below the first layer, a fourth layer of sand five centimeters deep was discovered. Radiocarbon dating of the orange-like layer showed the sediment was likely deposited by tsunami around 1600.
The researchers also pointed out a sixth layer of whitish volcanic ash deposited by the eruptions in the 10th century that formed Lake Towadako, located along a border between Aomori and Akita prefectures, more than 200 kilometers away from here.
Finally, a blue-like eighth layer, which is 0.8 to 1 meter below the surface, shows the tsunami deposits made between the 8th and 9th centuries, the researchers said.
Ryoichi Shiratori, a lecturer of archaeology studies at Shokei Gakuin University in Miyagi Prefecture who carried out the research, insisted that the record is precious.
Shiratori said, “The geographical layers show that tidal tsunami swept over this area three times.”
He added, “They will be precious materials for future education of disaster prevention,” much like the Nojima Fault Preservation Museum in Awaji, Hyogo Prefecture.
That facility preserves an exposed fault line in the Great Hanshin Earthquake that struck the Kansai region at 5:46 a.m. on Jan. 17, 1995, to give people an opportunity to learn from the disaster.