Laura Smith
On 6 August 1945, the world witnessed the first-ever atomic bomb attack when the Little Boy bomb was dropped on Hiroshima, Japan. The attack, which occurred at 8:16 am, resulted in a mushroom cloud that rose to over 60,000 feet in about ten minutes. The cloud, visible from 30,000 feet above, was captured in a rare photograph discovered in a former Japanese elementary school. This photo, taken within 2 to 5 minutes of the blast, offers a glimpse into the immediate aftermath, showcasing the distinct two-tiered cloud as seen from Kaitaichi, six miles east of Hiroshima's centre.
| Characteristics | Values |
|---|---|
| Date | 6 August 1945 |
| Height | 40,000-60,000 feet (over 12 km) |
| Cause | Nuclear explosion |
| Type of explosion | Atomic bomb |
| Death toll | 70,000+ |
| Type of cloud | Mushroom-shaped flammagenitus cloud |
| Composition | Debris, smoke, condensed water vapour |
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What You'll Learn
- The Hiroshima mushroom cloud rose to over 60,000 feet in 10 minutes
- It was caused by the first atomic bomb, nicknamed Little Boy
- The cloud was two-tiered, visible from 400 miles away
- The explosion instantly killed 70,000 people, with more dying later
- Nuclear experts dispute the 'mushroom cloud' label for the smoke plume
The Hiroshima mushroom cloud rose to over 60,000 feet in 10 minutes
On 6 August 1945, the US aircraft Enola Gay dropped an atomic bomb on Hiroshima, Japan. This was the first time an atomic bomb was used in warfare. The explosion instantly killed over 70,000 people and destroyed two-thirds of the city.
The bomb, nicknamed Little Boy, exploded in the sky directly above Shima Hospital. Within a fraction of a second of the detonation, the temperature at ground level exceeded 7,000 °C (12,600 °F). A powerful blast wave scoured the landscape, and a massive mushroom cloud rose to a height of more than 60,000 feet in about ten minutes.
The mushroom cloud is a distinctive mushroom-shaped flammagenitus cloud of debris, smoke, and usually condensed water vapour resulting from a large explosion. The effect is most commonly associated with a nuclear explosion, but any sufficiently energetic detonation or deflagration will produce a similar effect. They can be caused by powerful conventional weapons, including thermobaric weapons.
The Hiroshima mushroom cloud was visible from a distance of nearly 400 miles. There are very few photographs of the cloud from the vantage point of the ground. One such photograph was discovered in a former Japanese elementary school in 2015. The photograph was taken from Kaitaichi, six miles east of Hiroshima's centre.
Nuclear experts have debated whether the Hiroshima mushroom cloud was, in fact, a mushroom cloud. Some claim that the image shows billowing smoke from a raging firestorm rather than a mushroom cloud.
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It was caused by the first atomic bomb, nicknamed Little Boy
The mushroom cloud over Hiroshima was caused by the detonation of the first atomic bomb, nicknamed "Little Boy". This bomb was created by the Manhattan Project, a highly classified project during World War II, and was the first nuclear weapon used in warfare. It was dropped on the Japanese city of Hiroshima on August 6, 1945, by the Boeing B-29 Superfortress "Enola Gay", resulting in widespread death and destruction.
"Little Boy" was a gun-type fission weapon that used enriched uranium -235 to power its explosive reaction. The design involved firing one sub-critical uranium projectile at another through a gun barrel, causing them to collide and form a critical mass that initiated a highly explosive fission reaction. This reaction released a massive amount of energy, with an explosion radius of approximately 1.3 kilometres, causing catastrophic damage to the city.
The mushroom cloud that formed over Hiroshima is a distinctive result of a large explosion, particularly associated with nuclear detonations. The cloud rapidly rose to over 60,000 feet in about ten minutes, towering even over the Enola Gay, which was flying at 30,000 feet. The city of Hiroshima was engulfed in thick black smoke and the immediate effects of the blast caused immense destruction and loss of life.
The photograph discovered in a Japanese elementary school provides a rare glimpse of the two-tiered mushroom cloud shortly after the explosion. It captures the unique shape of the cloud, which resulted from the Rayleigh-Taylor instability formed as the hot gases rose and changed shape due to atmospheric friction. The stem of the mushroom cloud is formed by the downward vortices and the afterwinds that draw in dirt and debris from the ground.
The "Little Boy" bomb was named by scientists involved in the Manhattan Project, possibly alluding to its predecessor design, the "Thin Man". The development and use of "Little Boy" marked a significant turning point in history, ushering in the Atomic Age and demonstrating the unprecedented destructive power of nuclear weapons. The bombing of Hiroshima had far-reaching consequences, leading to the establishment of organisations like the Atomic Bomb Casualty Commission to study the radiation effects and track injuries among survivors.
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The cloud was two-tiered, visible from 400 miles away
The bombing of Hiroshima on August 6, 1945, marked the first use of atomic weapons in war. The U.S. aircraft dropped an atomic bomb on the Japanese city, instantly killing more than 70,000 people out of a population of 343,000 inhabitants. By the end of the year, the death toll had surpassed 100,000, with two-thirds of the city destroyed.
The blast produced a distinctive mushroom cloud, which rose to a height of over 40,000 feet (12 km) in about ten minutes. The cloud was visible from 400 miles away. The two-tiered cloud was observed from Kaitaichi, now part of Kaita, six miles east of Hiroshima's centre. There are very few photographs that capture the cloud from the ground, with most images taken from the Enola Gay as it circled to get a better look at the explosion.
A mushroom cloud is a distinctive mushroom-shaped flammagenitus cloud of debris, smoke, and usually condensed water vapour resulting from a large explosion. They are most commonly associated with nuclear explosions, but any sufficiently energetic detonation or deflagration will produce a similar effect. The buoyant mass of gas rises rapidly, forming turbulent vortices that curl downward, creating a temporary vortex ring that draws up a central column of smoke, debris, or water vapour to form the "mushroom stem".
The Hiroshima mushroom cloud was not the first to be documented. A 1782 attack on Gibraltar by the Franco-Spanish attacking force produced a floating battery explosion with a mushroom cloud. In 1798, Gerhard Vieth published an illustrated account of a cloud in Gotha that was "not unlike a mushroom in shape".
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The explosion instantly killed 70,000 people, with more dying later
On 6 August 1945, the world's first atomic bomb attack took place in Hiroshima, Japan. The bomb detonated over the city at 8:16 a.m., instantly killing 70,000 people. The blast generated a mushroom cloud that rose to over 60,000 feet in about ten minutes. The cloud was a distinctive, mushroom-shaped cloud of debris, smoke, and condensed water vapour resulting from the large explosion. The effect is commonly associated with nuclear explosions.
The immediate aftermath of the blast was captured in a photograph discovered in a former Japanese elementary school. The picture, taken from Kaitaichi, six miles east of Hiroshima's centre, shows the two-tiered cloud. The image is one of the only known photographs capturing the cloud from the ground.
The blast and the resulting radiation had devastating effects on the people of Hiroshima. Many of those who survived the initial explosion later died from radiation exposure. The "black rain" that fell one to two hours after the explosion, a combination of ash, radioactive fallout, and water, caused severe radiation burns. The radiation also affected pregnant women, who experienced higher rates of miscarriage and infant deaths.
The total number of deaths resulting from the Hiroshima bombing is difficult to estimate due to the extensive destruction of civil installations, the state of confusion following the explosion, and the uncertainty of the population before the bombing. However, by the end of 1945, the bombing had killed an estimated 140,000 people in Hiroshima, with many more dying from the long-term effects of radiation exposure, including increased rates of cancer and chronic diseases.
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Nuclear experts dispute the 'mushroom cloud' label for the smoke plume
The Hiroshima bombing generated a towering plume of smoke, rising to over 60,000 feet in about ten minutes. The smoke plume was captured in a rare photograph, discovered in a Japanese elementary school, providing a glimpse of the immediate aftermath of the bombing.
However, nuclear experts dispute the "mushroom cloud" label for this smoke plume. Richard L. Garwin, a noted bomb designer and longtime adviser to Washington on nuclear arms, asserted that the image did not depict a mushroom cloud. Kevin Roark, a spokesman at the Los Alamos weapons laboratory in New Mexico, which created the Hiroshima bomb ("Little Boy"), concurred, describing the image as "a smoke plume from the fires that followed."
Roark's assertion is supported by the scale of the cloud. He argues that if the cloud were nuclear in nature, it would be larger than the one resulting from the most powerful bomb the United States ever detonated, which was a thousand times stronger than Little Boy. Military experts also analysed the shadow of the cloud in the photograph, concluding that the picture was taken by an American plane just before noon, more than three hours after the bomb was dropped. This timing suggests that the original mushroom cloud had long since dissipated, further supporting the argument that the photographed plume was not the mushroom cloud.
While the Hiroshima smoke plume has been a subject of debate, the term "mushroom cloud" is commonly associated with nuclear explosions. The distinctive mushroom shape is formed by the rapid rise of a large volume of lower-density gases, resulting in turbulent vortices that curl downward to form a temporary vortex ring. This upward movement of gases creates a mushroom stem, often containing smoke, debris, and condensed water vapour. Mushroom clouds have been observed and described for centuries, but their association with nuclear explosions is a more recent phenomenon, with the term "mushroom cloud" possibly coined in the early 1950s.
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Frequently asked questions
The mushroom cloud rose to over 60,000 feet in about ten minutes.
The bomb was released from the plane at 9:15 AM local time, and detonated at 9:16 AM.
The plane that dropped the bomb was the "Enola Gay", a B-29 Superfortress.
The bomb dropped on Hiroshima was a uranium bomb nicknamed "Little Boy". It weighed nearly 10,000 pounds and exploded with the force of more than 15,000 tons of TNT.
