Science

Archaeology: ‘Mass grave’ was buried under volcanic ash 1000 miles from eruption

Yellowstone supervolcano has been the source of intense research by scientists for many decades. It has blown its top three times in history in what have been described as “supereruptions”: eruptions that are approximately 1,000 times more powerful than the Mount St Helens eruption of 1980 which is often considered the most disastrous volcanic eruption in US recorded history. While there are no signs Yellowstone will erupt any time soon, scientists regularly analyse the potential effects of a blast given the scale of previous eruptions.

Volcanic ash is made of tiny particles of jagged rock, minerals and volcanic glass, sometimes so fine that it can be inhaled.

Breathing in large amounts of volcanic ash can cause a person to suffocate, which is the most common cause of death from a volcano.

To investigate the effects of what happens to those who inhale volcanic ash, archaeologists have found a perfect case study in Nebraska.

Michael Voorhies, a palaeontologist and earth scientist, made a breakthrough discovery in the Seventies which was detailed in the 2004 Naked Science documentary ‘Super Volcanoes’.

He explained: “I was prospecting for fossils here and came across this volcanic ash bit.

“Right at the bottom of the ash bit was the skull of a baby rhinoceros sticking out.”

It proved the start of an incredible discovery as beneath ten feet of ash stood an ancient waterhole — a snapshot in time from a Yellowstone hotspot eruption 10-12 million years ago.

Filled with the skeletons of horses, camels and rhinos, the waterhole was in a remarkable state of preservation.

One rhino was still bearing her unborn foetus, while other animals retained the contents of their last meal.

The documentary’s narrator said: “The mass grave contained over 200 animals. All died within days of each other.”

Scientists tested the ash, and were shocked to find that it had come from a now-extinct volcano almost 1,000 miles (1609 kilometres) — from the Bruneau-Jarbidge caldera in present-day Idaho, which overlaps the Yellowstone hotspot.

A hotspot is an unusually hot area in the mantle, beneath the Earth’s crust. The intense heat causes the mantle in that region to melt, and volcanic plumes rise up, breaking through the crust to form a volcano.

The ash saw animals within 100 miles (160.9km) of the blast die of suffocation and burn in pyroclastic flows, while animals further away died of slow suffocation as they were blanketed in ash.

Their bones showed that they had died of lung failure as a result of ash inhalation.

The smaller animals with smaller lung capacities died first, with the larger animals surviving just a matter of hours or days longer.

Explaining how the animals would have died, Mr Voorhies said: “The ash is so fine that it drifts easily in the wind.

“So it probably took maybe six or seven hours for the ash to get to Nebraska from the volcano.”

He added that the ash is so fine that it makes dust easily capable of getting into both human and animal lungs.

Unlike normal fossils, every single bone found was covered in a strange white substance — the sign of new bone growth.

The narrator said: “It’s a classic sign that an animal has died of the rare lung ailment known as Marie’s disease.

“As the lungs fail, the skeletal system goes out of control, rapidly depositing new bone on top of old.

“It reveals that the animals died a slow and painful death, as their lungs, choked by ash, started to fail.

“It caused their bones to grow thicker. Racked with pain, they were drawn to the waterhole, where they died, all within a month of the eruption.”

The site is now a National Natural Landmark, having been awarded such status in 2006.

Specially constructed walkways allow tourists to watch palaeontologists at work during the summer season.

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