Deep in the basement beneath Chernobyl's destroyed Reactor 4 lies a mass of black lava-like material shaped roughly like an elephant's foot. This is the 'Elephant's Foot' - about 2 meters wide, weighing several tons, formed when the reactor's nuclear fuel melted through the floor and mixed with concrete, sand, and other materials during the 1986 disaster. In the months after the explosion, the Elephant's Foot was so radioactive that spending 30 seconds in its presence would cause dizziness and fatigue. Five minutes would kill you within days. It may be the most dangerous object on Earth - and it's still there, slowly decaying in the ruins of the world's worst nuclear accident.
On April 26, 1986, a safety test gone wrong caused Reactor 4 at Chernobyl to explode. The graphite moderator caught fire. The nuclear fuel, at temperatures exceeding 2,000°C, melted through the reactor vessel. This superheated mass - called corium - poured through the floor.
The corium encountered concrete, sand (thrown by helicopters to smother the fire), and other materials. It melted through multiple floors, forming flows and puddles of radioactive lava. When it finally cooled and solidified, it left behind formations of extraordinary danger. The largest and most famous was the Elephant's Foot.
The Elephant's Foot was discovered in December 1986 by workers exploring the basement of Reactor 4's destroyed building. Located in a corridor beneath the reactor hall, the black, glassy mass emerged from a crack in the wall. Its shape vaguely resembled an elephant's foot - hence the name.
Approaching it was suicide. Radiation levels at its surface exceeded 10,000 roentgens per hour. Even at distance, the radiation was intense enough to fog camera film. The first photographs were taken by sending cameras on long poles into the corridor, or by mounting them on remote-controlled robots that often failed in the intense radiation.
The Elephant's Foot is composed of a material scientists call Chernobylite - a type of corium specific to this disaster. It contains uranium dioxide from the reactor fuel, zirconium from fuel rod cladding, concrete from the building, sand, graphite, and various other materials that melted together.
The mass is not uniform. Different regions have different compositions and radioactivity levels. The surface has a glassy texture from rapid cooling. The interior remains partially crystalline. Analysis has been difficult because samples are deadly to collect. Scientists know more about the surface of Mars than about the interior of the Elephant's Foot.
In 1986, the Elephant's Foot emitted approximately 10,000 roentgens per hour. An exposure of 500 roentgens is typically fatal. Standing next to the Elephant's Foot for 30 seconds would cause severe radiation sickness. Five minutes would be lethal within a week. Even the brief exposures needed to photograph it were dangerous.
Over time, radioactive decay has reduced the danger. By 2001, emission had dropped to about 300 roentgens per hour - still lethal with prolonged exposure but no longer instantly deadly. Today, the radiation continues to decline, but the Elephant's Foot remains extraordinarily dangerous and will be for centuries.
The Elephant's Foot cannot be removed. It is too large, too heavy, and too dangerous to transport. It will remain in place as long as the destroyed reactor remains, slowly crumbling as radiation damages its crystalline structure. Over thousands of years, it will decay into less hazardous materials.
The New Safe Confinement - a massive steel shelter completed in 2016 - now covers the entire destroyed reactor and its contents, including the Elephant's Foot. The shelter is designed to last 100 years, buying time to develop methods for dealing with the radioactive remains. The Elephant's Foot, the most deadly souvenir of humanity's worst nuclear accident, will outlast everyone alive today. It is a reminder that some mistakes cannot be undone.
Chernobyl (51.39N, 30.10E) lies in northern Ukraine, 100km north of Kyiv. Boryspil International Airport (UKBB) is 130km southeast. The Exclusion Zone surrounding the plant is visible from the air as an area of abandoned villages and regrown forest. The New Safe Confinement structure is clearly visible covering Reactor 4. The area remains off-limits except for guided tours. The Elephant's Foot is deep underground and not visible.