Large amber deposits discovered in northern Japan were likely swept out from a forest to the ocean by one or more tsunamis between 116 and 114 million years ago (Early Cretaceous epoch), according to new research led by the Geological Survey of Japan and Chuo University.
Amber deposit from Shimonakagawa Quarry in northern Hokkaido, Japan. Image credit: Kubota et al., doi: 10.1038/s41598-025-96498-2.
Traces of ancient tsunamis are hard to identify, as the waves can reshape coastlines and the deposits they leave can be difficult to distinguish from those caused by other high-energy events, such as storms.
However, amber, formed on land and transported to the ocean, could provide a record of tsunami events, with changes to the structure of the deposits suggesting physical processes that they were subjected to during this relocation.
“Tsunamis are catastrophic sea waves mainly caused by dramatic submarine/coastal crustal shifts and asteroid impacts,” said Dr. Aya Kubota, a researcher with the Geological Survey of Japan and Chuo University, and colleagues.
“They attract attention from the standpoint of disaster prevention and have therefore been studied intensively in Holocene (11,700 years ago to the present) coastal deposits.”
“With the exception of asteroid deposits, the unambiguous recognition of pre-Holocene paleotsunamis is very difficult for two significant reasons.”
“Firstly, coastal tsunami deposits are easily eroded in that dynamic environment, and secondly, robust criteria for tsunami deposits are unestablished due to the difficulty of distinguishing tsunamis from other high-energy coastal events (e.g. cyclones).”
In their research, Dr. Kubota and co-authors analyzed amber-rich silica deposits from Shimonakagawa Quarry in northern Hokkaido that were deposited approximately 115 million years ago in the Early Cretaceous, while the region was on the deep sea floor.
Through fluorescence imaging, the authors observed that the amber samples are distinctly deformed with so-called flame structures, which form when amber is still soft when deposited and changes shape before fully hardening.
This indicates that a large amount of the amber was rapidly swept out from the land to the open ocean by the backwash from one or more tsunamis, with limited exposure to the air.
The amber then sank to the sea floor where it was covered by a layer of silt and preserved.
“Other sediments originating on land and transported to open waters may be useful for investigating major ancient destructive events such as tsunamis,” the researchers concluded.
Their paper was published on May 15 in the journal Scientific Reports.
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A. Kubota et al. 2025. Amber in the Cretaceous deep sea deposits reveals large-scale tsunamis. Sci Rep 15, 14298; doi: 10.1038/s41598-025-96498-2
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