Hawaii’s Kilauea volcano could be bracing for another dangerous eruption after a pond of water was discovered inside its summit crater.

Last year, Kilauea, which had been erupting continuously for nearly 35 years, spewed lava that destroyed hundreds of homes on the Big Island.

Researchers with the US Geological Survey have now confirmed the presence of water at the bottom of the Halema’uma’u crater, which was previously home to a lava lake.

This is the first time in recorded history that water has been discovered on the floor of Kilauea’s crater.

“I am a bit surprised that water could accumulate to make a lake at Kilauea because the rocks are so permeable,” Michael Manga, professor of Earth and planetary science at the University of California, Berkeley, wrote in an email. “I would have guessed that the lake water would drain.”

Researchers say the presence of water could have different effects on Kilauea.

“Until we have a better understanding of where the water is coming from, it’s difficult to forecast what could happen next,” Janet Babb, a geologist with the Geological Survey’s Hawaiian Volcano Observatory, wrote in an email.

Babb does not believe that anything unusual will happen in the next weeks or months, but she says it’s likely that lava will return to Halema’uma’u. Lava could enter the crater to form another lava lake, or it could react violently with the water and create explosions if the lava rapidly rises through the water.

“Water plus heat (from magma/lava) makes steam, and steam can expand tremendously, which can break up lava into small bits and hurl them into the air,” Babb wrote. “However, there is no evidence that an explosion, under the current conditions, would increase risk to public safety (i.e., any explosion would be small).”

According to the Geological Survey, explosive eruptions can occur when the magma column drops below water table (the level below in which the ground is saturated with water), groundwater interacts with hot rocks, or steam pressure builds and then explodes.

The most powerful explosions at Kilauea since the early 19th century came in 1924, when groundwater came into contact with hot rocks, generating powerful explosions caused by steam.

“When magma comes in contact with lake water the explosions can be more energetic and more explosive,” Manga said.

If lava were to rapidly rise, that would be a much bigger concern.

“Lava fountains are driven by rapidly ascending lava and gas,” Babb said. “If lava fountains erupt through water, steam is produced, which helps drive the fountains higher.”

Kilauea alternates between explosive and effusive (slower, steady lava flows) periods, but with the added presence of water, the next explosive period could result in a massive collapse of the caldera floor.

“Kīlauea remains an active volcano, and it will erupt again,” the Geological Survey wrote in a report July 31. “Although we expect clear signs prior to the next eruption, the time frame of warning may be short.”

Correction: A previous version of this story misstated how a lava lake could form.