Japan’s tsunami created large dunes on the ocean floor

The Tohoku-oki earthquake and tsunami brought unimaginable devastation to the coastal areas of Japan in March 2011. But as a new study in Marine Geology suggests, it also reshaped the ocean floor, forming large underwater dunes as the massive waves rolled into the eastern seaboard, and then slowly pulled away.

The study, which was conducted by Kazuhisa Goto, a geologist at Tohoku University in Japan, relied upon data collected by a research team that went out into Kesennuma Bay about twenty days after the tsunami. The data, which was collected to assess the safety of the area for incoming ships, was used by Goto to chart the topological characteristics of the seafloor.

Japan’s tsunami created large dunes on the ocean floor

The area being studied was about 55 miles (90 km) northeast of the city of Sendai — so it was fairly far out. When the tsunami rolled over this particular area of the Pacific, the waves reached a height of 36 feet (11 meters), and it disturbed the sandy and silty seafloor 30 to 50 feet (10 to 15 m) below.

Goto discovered that the tsunami created dunes up to 65 feet (20 m) long and 6 feet (1.8 m) high. These dunes were not present on the seafloor before the 2011 tsunami. It's the first direct evidence that tsunamis can rework sea bottom sediments — and even influence a marine ecosystem.

The research team is not certain how many dunes the tsunami may have created. But in conversation with Our Amazing Planet, Goto said: "The tsunami wave current was very strong and I would not be surprised if dunes were formed across the entire bay, plus slightly deeper areas, but some of them may have been erased since then by normal post-tsunami wave activity."

As a result of their findings, Goto is recommending that marine ecosystems be monitored following significant tsunamis.

Read the entire study at Marine Geology. Goto has a related study in the same issue that can be accessed here.

Supplementary source: Our Amazing Planet.

Top image: NASA. Inset image via Tohoku University.