The ‘Devil’s Washboard’ is not the name of a surf punk band nor is it a haunted road in Kansas where 7 teenagers perished in the 50’s. It is the most geologically unique feature I have ever seen on a coast, and lies on Aoshima Island in the far southeast corner of Japan, an area thought to be the birthplace of the first Emperor Jinmu.
The region has a subtropical feel brought by the Black Current (or Kuroshio Current) that flows up from the southern Pacific. The neat rows upon rows of evenly eroded rock look like a huge washboard that a giant monster would use such as ‘Oni‘, a Japanese demon or devil and the inspiration behind the name.
The Japanese devil ‘Oni’ is an ogre-humanoid-like creature with wild hair and horns. Painting from 17th century.
I found it difficult to get answers on how the ‘Devil’s Washboard’–or the myth behind it–was formed, in part due to the language barrier that was especially evident in this corner of the country, where very few non-native tourists visit, and very few locals speak English.
When I returned to the States, I asked Dr. Leslie Sautter, a marine geologist and associate professor at the College of Charleston how it was likely formed. Her thoughts were that the formation appears to be the result of hundreds of layers of basalt from individual lava flows. These layers have either been tilted by tectonic activity or they formed atop the slope of a former volcano.
The space between the layers is probably marine sediment, which would point to the feature having been formed either underwater. The middle space is clearly less resistant to weathering and has eroded, yet it’s bracketed by the prominent ridges of stronger basalt layers and uniformly flattened by wave action.
The ‘Devil’s Washboard’ is completely hidden at high tide but at low tide the expanse is hard to capture in a single frame (see video below). The exposed rock, tide pools and rocky shores draw day-trippers and shellfish collectors who harvest a variety of marine invertebrates from the ragged edges.
Also to note: the area is a popular surf destination and just one of over 60 (named) spots along the entirety of Japan.