Very early warning system: ancient tsunami markers

The meaning of a place is frequently communicated by the means of markers. For example, a typical American convention for marking the site of a historic (read “culturally significant”) event is by the means of a large boulder with a metal plaque affixed to it. You can see a lot of these markers at the Historical Marker Database site.

But there are other types of markers that communicate the significant properties of a place. Travel down the King’s Highway in southwestern New Jersey, and you will find some old stone mile markers. The only significance of a mile marker is to communicate where that place is in relation to some other place, but to a weary traveler that knowledge could be very welcome indeed. (Here’s a photo of a King’s Highway mile marker at a place three miles from Salem and 31 miles from Camden.)

Another type of marker is detailed in this San Francisco Chronicle article (originally from AP):

Tsunami-hit towns forgot warnings from ancestors

The old Japanese stone markers described in the article are of different types. Some warn about what to what to do in case of a tsunami: “Always be prepared for unexpected tsunamis. Choose life over your possessions and valuables,” reads a marker in Kesennuma, which was very hard hit by the 9.0 Tohoku quake and tsunami. Another marker in Aneyoshi reads, “High dwellings are the peace and harmony of our descendants. Remember the calamity of the great tsunamis. Do not build any homes below this point.”

The article states:

“Hundreds of such markers dot the coastline, some more than 600 years old. Collectively they form a crude warning system for Japan, whose long coasts along major fault lines have made it a repeated target of earthquakes and tsunamis over the centuries.”

I’d quibble with the term “crude;” it seems that the people who made these markers used the best technology they had at the time. Stone is a durable material, and markers in public places are visible to all who pass by. Granted, one needs to be literate in order to read the stone’s message, but it seems likely that even illiterate members of the community would have known the message, if only because they had been told it by others in the community.

I’m sure that much more scholarship exists on the subject of these markers. I’m curious to know about the ages of the markers. I also wonder whether markers tended to be set up soon after a devastating tsunami had occurred; one point the article makes is that memories of tsunamis persist for relatively few generations. After the living memory dies out, people start building near the coastline again. Major seismic events occur on a very long scale of time, so a more permanent warning against their effects is necessary. Another thing I wonder about is whether those who made these markers intended that their warnings would still be visible centuries into the future.

H/T @Allochthonous