THOUSANDS of miles of red hot magma is waiting to burst from the world’s most dangerous volcano, experts in Britain have revealed.

Yellowstone super volcano in Wyoming, US, has laid dormant for 70,000 years with its chancing of blowing being slim – until now.

Boffins have now found 11,000 cubic miles of magma is sitting in underground reservoirs that are acting like “sponges” and are ready to burst into the atmosphere.

So much of it spewing into the air could block out sunlight and trigger a nuclear winter or even a mini ice age.

An international team of geologists found the most powerful eruptions are triggered by a slow drip feed of magma from large reservoirs deep within the Earth’s crust into smaller reservoirs closer to the surface.

These large reservoirs draw in hot magma from the Earth’s mantle and exist as large volumes of partially molten rock that are able to store magma like a sponge.

By conducting a number of numerical simulations of this process, the experts discovered that these large reservoirs are crucial to generating the largest volcanic eruptions on Earth.

But, fortunately, the team – including boffins from Cardiff University – also showed that these large reservoirs can take millions of years to form, hence why "super-eruptions" happen so rarely.

Yet worryingly, Yellowstone is believed to have seen super eruptions at intervals of two million, 1.2 million and 640,000 years ago, meaning another one could be due any time.

Co-author of the study Dr Wim Degruyter, from Cardiff University’s School of Earth and Ocean Sciences, said: “Our current understanding tells us that hot magma can be injected from the Earth’s lower crust into colder surroundings near the surface.

"At this point, the magma can either erupt or cool down to such a point that the magma solidifies and an eruption does not occur.

“Up until now, this theory hasn’t been able to explain how the magma can maintain its heat in these near-surface reservoirs and thus produce extremely powerful eruptions.

“Our study has shown that the key to this is much larger reservoirs deeper below the surface that are able to slowly increase the temperature in the upper part of the crust such that it becomes more amenable to the storage of magma.

"When the crust has become fully mature, giant reservoirs are able to form in the upper crust and thus we see extremely powerful eruptions.”

Previous research revealed that a deeper magma body connects to a magma reservoir in the upper part of the crust underneath Yellowstone, which spreads across the sates of Wyoming, Montana and Idaho.

The deeper magma body sits 12 to 28 miles below the surface and it’s believed that the hot molten rock could fill the 1,000-cubic-mile Grand Canyon 11.2 times.

It is believed that the last super eruptions at Yellowstone were fed by the volcanic plumbing system that sits beneath it.

Dr Degruyter added: "Our calculations appear to agree with the observations that have been made at Yellowstone.”