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If you look at it just right, the universal radiation warning symbol looks a bit like an angel. The circle in the middle could indicate the head, the lower part might be the body, and the upper two arms of the trefoil could represent the wings. Looking at it another way, one might see it as a wheel, a triangular boomerang, a circular saw blade, or any number of relatively benign objects. Whatever a person’s first impression of it may be, someone unfamiliar with the symbol probably wouldn’t guess that it means “Danger! These rocks shoot death rays!”

The U.S. Department of Energy has been grappling with that problem recently, as they designed the warning markers to use at Yucca Mountain and at the Waste Isolation Pilot Plant (WIPP) nuclear waste storage facilities. There’s no telling who might be around to exhume our radioactive sins in future centuries, but the Environmental Protection Agency (EPA) mandates that warnings be erected which will warn away potential intruders for the next 10,000 years, whomever those intruders may be.

The offending nuclear waste will be stored far underground at each of these facilities, but there is still a danger that future generations might stumble across it. WIPP is located in the desert outside Carlsbad, New Mexico, and its storage areas are located 2,150 feet underground. Yucca Mountain’s facilities in the Nevada desert are intended to house waste at 1,000 feet deep. Between the two, they are meant to entomb tens of thousands of metric tons of nuclear waste, most of which will remain dangerous for centuries. Each of these locations was selected due to its relative geologic stability, theoretically allowing facilities there to contain the waste for the required 10,000 years.

Ten thousand years ago, early humans were still painting images on the walls of caves. Some of those primitive messages managed to survive ten millennia, and they also remain somewhat meaningful. But of course our ancient cave-painting ancestors weren’t attempting to illustrate complex ideas as far as we know.

Before one can communicate with unknown future societies about deadly nuclear waste, it is important to consider with whom precisely one is trying to communicate. Such people may be part of a highly advanced civilization, they may be a society much less advanced than our own, or they may have comparable technology to that which we have today. Further, they may not be directly descended from local cultures. Messages will thus need to communicate to anyone⁠— regardless of their culture, technology, or political structure⁠— that intruding upon the repository is not in their best interest.

The essence of the message itself is simple: Warning, dangerous materials are buried below. But how to communicate this to all possible discoverers using an enduring medium? To help answer this question during the preparations for the WIPP facility, panels of experts were assembled comprised of individuals with backgrounds in history, future studies, economics, law, physics, sociology, geography, engineering, political science, risk analysis, agriculture, climatology, history, and demographics. This group was called the Futures Panel, and they were tasked with creatively exploring the possible reasons why a future society might penetrate these deep underground storage facilities. They were also asked to advise on how to universally warn away would-be intruders.

The potential causes of future intrusion were imagined to be: water impoundment, resource exploration/extraction, scientific investigations, archaeological exploration, reopening the facilities for additional storage, waste disposal by injection wells, explosive testing, underground transportation tunnels, and weather modification. With these possibilities under consideration, the Futures Panel proceeded with the assumption that intelligent beings would halt any of these activities if the monuments were successful at conveying their warning. The panel roughly defined the intended message with the following:

This place is a message… and part of a system of messages… pay attention to it!Sending this message was important to us. We considered ourselves to be a powerful culture. This place is not a place of honor…no highly esteemed deed is commemorated here… nothing valued is here. What is here is dangerous and repulsive to us. This message is a warning about danger. The danger is in a particular location… it increases toward a center… the center of danger is here… of a particular size and shape, and below us. The danger is still present, in your time, as it was in ours. The danger is to the body, and it can kill. The form of the danger is an emanation of energy. The danger is unleashed only if you substantially disturb this place physically. This place is best shunned and left uninhabited.

The ideas that sprang from the panel were varied and interesting. It was decided that the markers would need to be designed to impart multiple levels of information, ranging from the rudimentary⁠— something made by humans is here⁠— to the more complex, such as the exact composition of the waste. This approach, coupled with redundancy, was hoped to allow future discoverers to realize that the site was significant, but also providing detailed information should future society have the means to read the data. They also pointed out that the markers should be made of ordinary materials and absent of beauty, lest the finders see value in removing the markers from the site.

Panelists described culture-independent ideas which are intended to trigger the danger reflex in all of humanity. One example indicated a massive “landscape of thorns,” made up of fifty-foot-high concrete spires with sharp points jutting out at all angles. Another intriguing idea was an arrangement of gigantic, black, “forbidding blocks” which are too close together and too hot to provide shelter.

Ultimately, the decision for the WIPP markers was motivated by cost-effectiveness. Current plans call for the area over the waste storage panels to be outlined by “earthen berms,” which is another way of saying “large piles of dirt.” These berms will be jagged in shape and will radiate out from a central, generally square area. The jagged nature of the berms is meant to convey a sense of foreboding, and the exact size, shape, and configuration of the berms will be such that they will not quickly be eroded or covered. The four corner berms will be higher than the others to provide vantage points to see the area as a whole. Inside the corner berms will also be buried concrete rooms containing highly detailed information, such as maps, the periodic table, and astronomical charts indicating the date that the facility was sealed. This data will be engraved upon stone slabs which are too large to be removed from the rooms’ entrances.

Inside of the square arrangement of berms, multiple granite “message kiosks” will be engraved with more basic information describing the site’s contents. This text will be provided in all of the official UN languages and Navajo (the local indigenous language). Additionally, space will be left on the kiosks for a future generation to inscribe the message in another language. The granite surfaces will be protected by a concrete “mother” wall, and the messages will be placed up high to prevent them from being defaced or buried by the desert sand.

Lastly, the berms and the area they surround will be peppered with underground “time capsules” at varying depths. These clay, ceramic, glass, and aluminum oxide disks will be inscribed with warning information, and may contain samples of wood to allow a future society to date the

markers using carbon-14 dating.

Yucca Mountain information center concept

The plans for the Yucca Mountain warning markers are a bit different. Twenty-five foot monuments are intended to be inscribed with text and pictographs warning visitors of the dangers below, as well as a series of nine-inch markers embedded in the earth. Surrounding the area will be several large information-center monuments in the shape of the universal radiation symbol.

Other creative suggestions have been put forward for these warning markers, some of them coming from outside of the official panels. For instance, one individual suggested planting genetically-engineered blue cacti at the site to indicate its importance. Another suggested leaving significant human remains above-ground at the site, to frighten off any who might stumble across it. Still others advised against erecting any warning monuments at all, worrying that the markers themselves⁠— if not properly interpreted⁠— may rouse the curiosity of their discoverers enough that they might explore further, to disastrous ends.

In any case, WIPP is not scheduled to be sealed until the year 2038, and Yucca Mountain may be operating well into the 24th century; so humanity still has a little time to contemplate its warning to the future.