In Kesennuma, Japan, there are gigantic slabs of stone, erected centuries ago, that warn of environmental catastrophe.

“High dwellings are the peace and harmony of our descendants," one reads. "Remember the calamity of the great tsunamis. Do not build any homes below this point.”

Some of the Tsunami stones were placed there over 600 years ago, in order to warn anybody who came across them not to build homes beyond them. Others were placed more recently, like the one mentioned above that was put up in 1933. Built after several major tsunamis across the centuries, the tablets use several different methods of conveying their message. Some list death tolls, others simply tell all who see it to drop everything and get up high after an earthquake. 

By design, they are supposed to endure through the centuries.

“The tsunami stones are warnings across generations, telling descendants to avoid the same suffering of their ancestors,” specialist in the history of natural disasters Itoko Kitahara told the New York Times.

The stones have often been adhered to, and have saved many lives from subsequent tsunamis. However, they highlight an interesting problem which we still haven't come up with a solution for: how do you convey danger to your descendants hundreds or even thousands of years in the future?

It's not just hypothetical, but something humanity has to undertake. Nuclear waste can last anywhere from 1,000 to 10,000 years, meaning any warnings we put up around waste storage sites will have to last long enough for our distant ancestors to understand them. Simply placing it in a large structure isn't enough – as the pyramids and every other large structure that humanity has seen fit to rummage through over the years will attest. The message would need to survive across all cultural and language barriers that might arrive between now and when some future human stumbles across the nuclear waste in 7,000 AD.

In the early 1980s, the Human Interference Task Force attempted to come up with solutions, ready for a nuclear waste storage facility that was proposed to be built near Las Vegas. They decided that any message left as a warning to future humans needed to convey three things: That it was even a message, that dangerous material is stored in the location, and then the hard part  – information about the types of dangerous substances stored in the facility.

A number of solutions were proposed, with varying degrees of wackiness.

The Atomic Priesthood is clearly one of the coolest, as it sounds like something that would be in Fallout long before Fallout even existed. Proposed by linguist Thomas Sebeok, the idea was that an "atomic priesthood" would be appointed by a council, who would then replace themselves as they grow old and retire and/or die. The priesthood  – actually comprised of experts rather than the religious folk  – would be responsible for passing on knowledge down the generations, partly through "artificially created and nurtured ritual-and-legend, which would be a "false trail" for the uninitiated, who would be steered away from the hazardous site for reasons other than the scientific knowl[e]dge." This would be used to ward off people visiting the sites, without giving away what they contain, should any nefarious actors come across it.

They would create an annual ritual, and the legend of what lies in these locations would be repeated, warding people off. In the meantime, as a backup, they would update any messages at the burial site every three generations or so, to ensure that it could be understood.

A more simplified version of this from Vilmos Voigt (sadly lacking priests) proposed that translations of signs near the site be updated every now and then. 

Perhaps the strangest of solutions (and that's saying something, given that a previous paragraph involved atomic priests) was proposed by author Françoise Bastide and semiotician Paolo Fabbri. They believed that the most sensible course of action was to breed "radiation cats", that would change color when they came near radioactive material. 

That was the easy bit. Like with the priesthood, the plan would be to install cultural legends and myths around cats that change color

The myths and fairy tales (why not) would then be passed on through poetry, paintings, and music. So hopefully when someone years from now came across a glowing cat, they would know to run like hell. Which, to be fair, you would probably do today as well.

Others have later suggested using the landscape to deter people from entering the sites, scenery that is "non-natural, ominous and repulsive" and conveys danger to anybody who sees it. As they get closer, the architect who proposed this suggested, there would be carvings of human faces contorted into horror.

Less bizarre ideas involved making sure that people could only access the sites using high-tech solutions, making it unlikely that people would stumble across it, figuring that anybody capable of getting in would have the equipment necessary to detect radiation as well.

More recently, solutions have strayed quite far the other way, seeking to keep future societies integrated with the facilities in order to keep the knowledge alive.

“You don’t have to try to scare people away by looking menacing and symbolising danger," James Pearson, who worked on the Preservation of Records, Knowledge and Memory Across Generations initiative told the BBC. "You need try to inform people of what’s there, so they can then make an informed decision for themselves.”