On Aug.1, scientists with the USGS Hawaiian Volcano Observatory snapped this photo of the Kilauea Volcano and the small, green patch of water at the bottom of its crater.

Hawaii's Kilauea volcano, which just quieted down after a 30-year active stint, harbors a previously unknown patch of water at the bottommost part of its crater, according to the U.S. Geological Survey. And it might have the potential to trigger explosive eruptions in the future.

A couple of weeks ago, a helicopter pilot flying over Kilauea noticed a small, green patch at the bottom of the volcano's crater. The pilot alerted his friend of the mysterious find, who then told his friend, Don Swanson, scientist emeritus at the Hawaiian Volcano Observatory, part of the U.S. Geological Survey (USGS).

On Aug. 1, scientists from the observatory flew over the site and confirmed that what they were seeing was in fact water. This is the first time water has been found to exist on the volcano. [Photos: Fiery Lava from Kilauea Volcano Erupts on Hawaii's Big Island]

More recent observations revealed that the patch of water actually consisted of three separate ponds, the largest of which is between 36 and 46 feet (11 to 14 meters) wide — with unknown depths, Swanson said.

The ponds most likely formed from groundwater seeping in through cracks in the rocks, Swanson said. Last year's large, damaging eruptions led to the collapse of the floor of the crater at the top of the volcano; the crater is now more than 1,000 feet (300 meters) deeper than what it was before the eruption. With this new access to groundwater, the ponds will likely continue to grow, he said.

"We have no reason to think that the ponds won't coalesce and grow into something that maybe would be large enough to be called a lake," Swanson told Live Science. "This is assuming that no eruption destroys it, of course."

An eruption could vaporize the water, which could be carried away as a steam cloud, he said. But if this doesn't happen, and the ponds keep growing larger, they could cause explosive eruptions, as the fast-rising magma rapidly heats that water into steam, Swanson said.

Such steam would then expand, break up the magma into tiny pieces called volcanic ash and eject them into the air, he said. What's more, if the magma was already filled with gas bubbles, they would also expand and help drive the explosion.

Either scenario could occur, and a combination of both could even arise, he said.

"We don't see anything in our monitoring data that might suggest an eruption is imminent," Swanson said. "One will certainly occur again — there's almost no doubt about that." Kilaeau has always been stir-crazy, and throughout its history, it has gone through periods of explosive and nonexplosive, slower eruptions. It's been in this relatively calmer state for the past couple hundred years.

"Although the explosion potential is there, it's very unlikely that it's going to be in the near term, because there's so little water in the ponds now," Swanson said. "What we're talking about is long term," or years before this would be of concern.

Originally published on Live Science.