Parts of Yellowstone National Park have been sectioned off after a newly formed thermal feature violently erupted scolding hot muck.
The unexpected eruption saw a section of the park in Wyoming, USA showered with a blistering mixture of water, soil and sinter - mineral deposits that are precipitated from hot springs.
Geysers that have been inactive for the last five years are also warming up and throwing scalding water around, which is a further sign that the park's hydrothermal systems are playing up.
Geysers are a type of hot spring with a pipe-like hole in the ground that connects to a subsurface reservoir of water.
Molten rock buried several miles inside the Earth's crust heats the water to boiling point, which builds pressure in the chamber and forces water towards the surface.
The remaining water begins to steam and eventually builds enough force to eject scorching hot water into the air.
The eruption happened on Geyser Hill, near the famous Old Faithful geyser.
Michael Poland, a research geophysicist and scientist-in-charge at the Yellowstone Volcano Observatory, told Live Science: "The activity seems to have started on May 24. These hydrothermal systems are incredibly dynamic - the one constant is change."
After two weeks of turmoil things are now cooling down but Mr Poland warns there is still some 'restlessness' there.
He added that Geyser Hill will probably return to its previous state but the new feature could remain intermittently active so park rangers may have to reroute the boardwalk.
Mr Poland said: "You can think of the system a bit like the plumbing in an old house. The pipes are corroded and might contain lots of mineral deposits, and small changes in pressure within the system can cause leaks to form."
Mr Poland said the unrest could be due to an 'awful' lot of snow in Yellowstone in the past year which has resulted in more excess water in the subsurface.
He added: "All of these factors together can influence how geyser and hot spring systems behave, and change over time."
In September 2018 there were similar incidents of violent eruptions including the Ear Spring geyser which ejected 80 years' worth of human trash.
