World's largest acidic geyser wakes up in Yellowstone from six-year slumber

The world's largest acidic geyser is putting on a show again, erupting for the first time in six years after a quiet hiatus, officials at Yellowstone National Park say.

The Echinus Geyser - located in the park's famous Norris Geyser Basin - had been in slumber since 2020, and it's unknown whether the eruptions will continue into the summer.

Researchers say geysers can sometimes become active for a month or two before falling dormant again.

"Geysers are always turning on and off. That's Yellowstone being Yellowstone!", the US Geological Survey wrote on X.

A geyser is a spring of water which has been heated geothermally, and which erupts at various rates.

It is formed from a tube-like hole that goes down into the Earth's surface and is filled with water. When the water at the bottom, which is near molten rock called magma, heats in the tube it begins to boil and is forced upwards and erupts.

After eruption, the water slowly goes back down into the tube. Then the process starts again.

The Echinus Geyser used to erupt at regular intervals, which is why viewing platforms were built around it.

In the 1970s, the geyser would erupt regularly at 40 to 80 minute intervals. In the decades after, the eruptions would sometimes last up to 90 minutes, blasting water as high as 75ft (23m) into the air.

The eruptions "could be vertical or inclined, occasionally soaking onlookers with warm water".

But the eruptions became less consistent, with only one recorded in 2018, one in 2019 and two in 2020.

The eruptions resumed on 7 February, and have now returned to 2017-era rates. These eruptions have lasted for up to three minutes, with water heights reaching up to 30ft.

It's unknown whether the geyser will continue to erupt during the busy summer tourist season.

"It's probably not too likely given the geyser's tendency to wake up for a month or two before going back to sleep, and there were no eruptions during the last few days of February so it might already have gone quiet," researchers say.

The Echinus Geyser gets its name from the rocks that surround it, which resemble sea urchins - a type of echinoderm.

It is unique, since most acidic geysers break down over time as the acid eats through the rock that funnels water towards its spout.

But it hasn't broken down because "the acid is not concentrated", according to the park.

"Rather, it's a bit like orange juice or vinegar," the USGS said in a statement on Monday.

"Acid geysers are rare because acidic water can break down the rock that makes up a geyser's plumbing system," the USGS explains.

"At Echinus Geyser, however, the composition is due to mixing between acidic gases and neutral waters, and the acidity is not sufficient to eat away at the rock."