The two eruptions took place 630,000 years ago and 170 years apart, a study of ash in the seafloor has revealed.
Scientists previously believed there had been one single blast in prehistoric California.
The cataclysmic explosion sent ash and sulphur pouring into the sky blocking the sun and causing the entire planet to cool.
University of California Santa Barbara geologist James Kennett said: “We discovered here that there are two ash-forming super-eruptions 170 years apart and each cooled the ocean by about 3 degrees Celsius.”
The discovery was made after research found two distinct layers of ash on the seafloor of the Santa Barabara Basin.
The sediment also contained key information about the temperature of the sea during this period which took a drive following the Yellowstone eruptions.
It is predicted that the cooling was intensified by snow and ice reflecting the sun’s warms out into space.
Prof Kennett said: “We see planetary cooling of sufficient magnitude and duration that there had to be other feedbacks involved.
“It was a fickle, but fortunate time.
“If these eruptions had happened during another climate state we may not have detected the climatic consequences because the cooling episodes would not have lasted so long.”
The US cities at risk of destruction from a Yellowstone super-eruption have been mapped.
Fears are growing a huge eruption is due, 630,000 years after the last blast sent debris flying hundreds of miles across America.
A modern eruption of the Yellowstone volcano, however, would explode over a very different America, with tens of millions of people now living on the land once covered with lava and ash.
These US cities are at risk in the event of another huge Yellowstone volcanic eruption.
Denver City is the biggest city at direct risk of a major blast, located around 500 miles to the south-east of the volcano.
In millennia past, the area had been covered by up to three feet of ash, which moved at “hurricane speeds” and boasted terrifyingly-hot temperatures as it flew across the country.
Doctor Hank Heasler, park geologist at Yellowstone, said: “This ash when it comes up is maybe about 2,000 degrees Fahrenheit.
“So very hot and then it moves laterally at hurricane force winds and that’s what causes a wide zone of destruction.”