Experts at Yellowstone National Park claim to have seen the Steamboat Geyser erupt on the evening of Thursday, March 15.
The activity has sparked fears among volcano watchers amid concerns the supervolcano, located about 15 miles south of the geyser, is due to erupt.
Jacob Lowenstern, former scientist in charge of the Yellowstone Volcano Observatory, told the Casper Star and Tribune: “As you get hotter and hotter and deeper and deeper, the permeability and ability of water to move around shuts off. There’s not a whole lot of connectivity of the reservoirs once you get deep.”
But to make the situation even more terrifying, there has been 11 earthquakes in the region since the geysers blew – more evidence of the subsurface action in the magma pits.
The strongest of the earthquakes was a 2.2 magnitude tremor which hit at 17.30 local time on March 18.
The other earthquakes have hovered around the magnitude 1 mark.
Typically, when there are tremors around a volcano, it is a sign the magma is recharging and could lead to an explosion.
Some who live in the US took to social media site Twitter to express their fears that the volcano is set to erupt.
Christian Meador wrote: “Is anyone else scared about the fact Yellowstone is a super volcano that could erupt any day now and effect the whole continent?”
D Hamilton added: “The worlds largest active super volcano may erupt at Yellowstone.”
The Yellowstone Caldera supervolcano last erupted 700,000 years ago but experts say it should blow every one million years or so.
If the Wyoming volcano were to erupt an estimated 87,000 people would be killed immediately and two-thirds of the USA would immediately be made uninhabitable.
The large spew of ash into the atmosphere would block out sunlight and directly affect life beneath it creating a “nuclear winter”.
The massive eruption could be a staggering 6,000 times as powerful as the one from Washington’s Mount St Helens in 1980 which killed 57 people and deposited ash in 11 different states and five Canadian provinces.
If the volcano explodes, a climate shift would ensue as the volcano would spew massive amounts of sulphur dioxide into the atmosphere, which can form a sulphur aerosol that reflects and absorbs sunlight.