Don't worry, there's only a 1 percent chance it will erupt.

Scientists have discovered a lava dome inside an underwater volcano in Japan that could potentially kill up to 100 million people if it were to erupt.

A team from the Kobe Ocean-Bottom Exploration Center (KOBEC) found the dome approximately 30 miles south of the Satsuma Peninsula in Kagoshima Prefecture, local news outlet The Mainichi reported. The dome measures about 2,000 feet high and about 6 miles in diameter.

“Although the probability of a gigantic caldera eruption hitting the Japanese archipelago is 1 percent in the next 100 years, it is estimated that the death toll could rise to approximately 100 million in the worst case scenario,” Professor Yoshiyuki Tatsumi, head of KOBEC and a magma specialist, told The Mainichi.

This Japanese supervolcano is not the only one with the potential to cause widespread damage, or even send an entire region into volcanic winter. A supervolcano inside Yellowstone National Park has the strength to spew ash across most of the continental U.S.

Yellowstone's supervolcano last erupted 600,000 years ago. A study from the University of Arizona found that while a volcanic eruption is not likely to occur soon, residents will have much less time to prepare than previously thought.

“It’s shocking how little time is required to take a volcanic system from being quiet and sitting there to the edge of an eruption,” study co-author Hannah Shamloo told The New York Times.