It’s been hundreds of thousands of years since the last eruption of the supervolcano that lurks beneath Yellowstone National Park.
Scientists have long worked to piece together what occurred during the ancient eruption, in efforts to better predict what could happen when it blows again.
Now, a study on volcanic ash found in seafloor sediments in California’s Santa Barbara Basin has revealed the cataclysmic event 630,000 years ago was not one, but two super-eruptions.
The eruptions, separated by 170 years, launched massive amounts of ash and sulfur dioxide, reducing the amount of sunlight reaching Earth’s surface and effectively plunging the planet into two distinct volcanic winters.
It’s been thousands of years since the last eruption of the supervolcano that lurks beneath Yellowstone National Park. A study on volcanic ash found in seafloor sediments has revealed the event was not one, but two super-eruptions. Artist’s impression pictured
BUILDUP TO ERUPTION
In a recent study, researchers analysed rocks from Yellowstone’s Lava Creek Tuff – a fossilised deposit of ash from Yellowstone’s last supereruption.
Their analysis revealed trace crystals in the ash which contained details of temperature, pressure and water beneath the volcano.
Dr Christy Till, an author of the study, said: ‘We expected that there might be processes happening over thousands of years preceding the eruption.’
But instead, the crystals revealed a rise in temperature and a change in composition that occurred on a rapid time scale.
This suggests that the last eruption occurred just decades after an injection of fresh magma beneath the volcano.
‘We discovered here that there are two ash-forming super-eruptions 170 years apart and each cooled the ocean by about 3 degrees Celsius,’ said UC Santa Barbara geologist Jim Kennett.
The researchers found two layers of volcanic ash in the seafloor sediments off the coast of Southern California contain the chemical fingerprint of the most recent Yellowstone super-eruption.
They also analyzed sediments that hold a geological record of ocean and climate changes over thousands of years.
This revealed there were two separate super-eruptions – and, they occurred at a time the planet was warming out of an ice age, the researchers say.
The Santa Barbara Basin is steadily fed by sediment from the land, with an influx of about one millimetre per year.
And, the ocean is highly productive, with nutrients upwelling from deeper waters.
Tiny foraminifera shells that sank to the sea floor were thus buried and preserved in this area.
As they contain temperature-dependent oxygen isotopes, analyzing these shells can reveal the sea surface temperatures from when the creatures lived.
The team compared this with the volcanic ash record, revealing there were two separate events – each of which drove dramatic climatic changes, temporarily causing Earth to cool.
Each of these events occurred abruptly – and, lasted longer than it should have, the researchers say.
Yellowstone National Park spans the midwestern US states of Wyoming, Idaho and Montana (pictured)
THE YELLOWSTONE EARTHQUAKE SWARM
At the beginning of October, researchers confirmed an ongoing earthquake swarm at Yellowstone is now one of the biggest ever, with 2,475 tremors recorded since it began in in June.
Records show that 115 earthquakes were reported in the western part of the national park during September alone.
The largest swarm ever to occur at Yellowstone took place in 1985, with more than 3,000 events over a three month period.
Experts at the US Geological Survey (USGS) released the data as part of a monthly update.
Of the 115 quakes, 78 were part of an ongoing swarm six miles north of West Yellowstone.
The biggest event in the swarm last month was magnitude 2.3, which occurred at 6.59pm Mountain Time (8.59pm ET / 1.59am Sep 4 BST).
This may have been the result of sea ice and snow cover, which would have reflected sunlight, or a change in ocean circulation.
‘We see planetary cooling of sufficient magnitude and duration that there had to be other feedbacks involved,’ Kennett said.
‘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.’