On April 26, 1986, a nuclear reactor melted down at the Chernobyl power plant in Ukraine. The accident, which, according to the Environmental Protection Agency (EPA), was caused by unauthorized testing, was one of the first and worst nuclear meltdowns in history. Now, nearly 30 years later, a large, lava-like puddle of radioactive material called the “Elephant’s Foot” is still burning beneath the reactor.

According to Nautilus, exposure to the Elephant’s Foot can cause a series of strange and horrifying ailments. For example, 30 seconds of exposure can cause dizziness and fatigue up to a week later. At two minutes of exposure, your cells start to hemorrhage, and by five minutes your lifespan shrinks to about two days, making the Elephant’s Foot one of the deadliest waste products on Earth.

So, what is it exactly? The Elephant’s Foot is made of a substance called corium, which is basically the melted portion of the reactor’s core, reports Forbes. When Chernobyl melted down, its core burned through the reactor and turned into molten corium. This waste material cooled in the basement of the reactor and formed something that resembles an elephant’s foot. When it was first discovered, back in 1986, about 30 seconds of exposure was enough to kill a person.

To understand how dangerous the Elephant’s Foot was, back when it was first found, researchers  had to wheel in cameras and equipment to make take readings while hiding at a safe distance. The formation is still studied today to see how its radiation levels drop over the years.

The picture above was taken about 10 years ago. However, the strange formation is still actively burning into the concrete under the melted down reactor. If the Elephant’s Foot burns down enough to hit ground water, it has the potential to cause a massive explosion or, as Nautilus warns, could poison a large amount of water with radioactive materials.

(h/t Nautilus, Forbes)