Siberia’s “gateway to the underworld” is already massive.

But, new research shows that it continues to grow, with the Batagaika Crater growing by 35 million cubic feet (1 million cubic meters) every year. The growth is caused by the constantly thawing ground around the crater. When the frozen ground melts, the walls of the crater cave in more, causing it to grow even larger. The crater, which was first discovered in 1991 when a section of hillside collapsed in the Yana Uplands of northern Yakutia in Russia, has seen layers of permafrost completely exposed to the constantly warming air. This “gateway to the underworld” is located within some of the oldest permafrost in the world. It has also been called “the mouth to hell” because of its massive size.

As more of this deeper ground is exposed, the rising temperatures are able to melt more and more of the layers beneath. It’s a terrifying truth that has raised some huge concerns about the ongoing climate change issues surrounding the state of our world. Rapid permafrost thawing is a huge issue that has unleashed some interesting discoveries, including the revival of an ancient zombie virus frozen for over 40,000 years. With the permafrost continuing to thaw, though, the rate of expansion for the gateway to the underworld may increase, as well.

If that happens, it will continue the ongoing chain reaction of causing even more permafrost to thaw, which may release more bacteria that the world hasn’t seen for thousands upon thousands of years. Considering this stretch of land has likely been frozen for up to 650,000 years, there’s no telling what secrets it might hold. The study featuring these findings is available in the journal Geomorphology, and it helps us better understand the way that the crater is changing.

Sure, not all climate change is caused by humankind.

But, with humanity’s actions around the world steadily adding to the pressure, it is unlikely we’ll see the crater stop growing anytime soon.