Hiroshima’s lost buildings found on beaches

20 May 2019

MUSHROOM-CLOUD

Atomic bomb mushroom cloud

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Huge amounts of material from the destroyed buildings of Hiroshima may have been hiding in plain sight ever since the nuclear explosion, according to new research from the University of California, Berkeley.

Geologists studying sand from beaches in southern Japan spotted tiny glass particles which they believe were formed during the blast from the atomic bomb that was dropped on the city on 6th August 1945.

The glass spheres, most less than a millimetre in size, are typically formed by meteorite impacts.

The energy of a meteorite hitting the Earth can cause temperatures so high that the ground itself melts and droplets are flung up into the atmosphere. As they fall, they cool very quickly and form small rounded pieces of glass.

Geologists expect to find such glasses at the sites of meteorite impacts, but were surprised by their presence in Hiroshima Bay, as this is not an area known to have had many meteorites landing.

“The debris does not at all match the composition of the ground, of the bedrock,” explains Mario Wannier, lead author of the study. Instead, the particles show signs of human-made material - some are fused to specks of rubber, or have traces of concrete or stainless steel.

“Of course, being in the bay of Hiroshima, only a few kilometres away from ground zero, the first and obvious explanation would be the atomic bomb,” says Wannier. “Everything matches the physical model that we have of conditions within the atomic cloud and the resulting formation of glasses.”

The energy produced in the detonation would have been enough to liquify buildings, and pull the droplets upwards into the mushroom cloud before they fell back to the ground.

So far, none of the glass spheres tested have been radioactive.

Similar glasses have been described being formed at nuclear test sites, including at the Trinity test in New Mexico in July 1945, where the desert sand melted into glass known as trinitite. These new particles have been dubbed “Hiroshimaites.”

The group plans to visit Nagasaki, the only other urban area to have suffered an atomic detonation, to see if they can find similar glasses there.

The identification of these glass particles as fallout from Hiroshima gives new opportunity to study exactly what happened to the city. “Scientifically, we can learn what happens to an urban environment when it is destroyed by an atomic bomb - that has never been described before, in the sense of the resulting debris,” Wannier explains.

The question of where the destroyed structures of the city had actually gone was understandably not a priority in the aftermath of the bomb, with focus being to study the levels and effects of the radiation. And yet, the question remained unasked even decades later.

“This is for me the most surprising element of the whole project, given the richness of this material, that we’ve discovered something so obvious that had never had the attention of anybody,” Wannier says.

The glass debris has been found up to 30km away, and is estimated to be thousands of tons in total.

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