Laura Smith
On 6 August 1945, the US detonated an atomic bomb over Hiroshima, Japan. The blast instantly killed or grievously wounded 80,000 people, with over 100,000 more dying from its effects in the coming months. The mushroom cloud rose to over 60,000 feet in about ten minutes. This article will explore the size and impact of the Hiroshima mushroom cloud, which was a harbinger of a new world of devastating nuclear weapons.
| Characteristics | Values |
|---|---|
| Height | 60,000 feet |
| Time taken to reach the height | 10 minutes |
| Time of bombing | 8:16 a.m. on August 6, 1945 |
| Number of people killed instantly or grievously wounded | 80,000 |
| Total number of deaths | 150,000-246,000 |
| Time taken for the fireball to reach its maximum size | 1 second |
| Maximum diameter of the fireball | 900 feet (274.32m) |
| Temperature on the ground | 7,000 degrees Fahrenheit (3871 Celsius) |
| Speed of the blast wave | 984 miles per hour (1583.59 kph) |
| Distance of Enola Gay from Hiroshima when it felt the shock waves | 18.5 km (11.5 mi) |
| Distance of the photographer from the hypocenter | 4 kilometers |
| Time taken by the photographer to capture the image after the explosion | 15 minutes |
| Height of Tsar Bomba cloud, the largest atomic test | 40 miles |
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What You'll Learn
The cloud rose to 60,000 feet in 10 minutes
On August 6, 1945, the world witnessed the first-ever atomic bomb attack when the Little Boy bomb was dropped on Hiroshima, Japan. The mushroom cloud that formed after the explosion rose to a height of 60,000 feet in about ten minutes. To put that into perspective, the plane that dropped the bomb, the Enola Gay, was flying at 30,000 feet, and yet the mushroom cloud rose above it.
The immense size of the cloud is a testament to the unprecedented nature of the atomic bomb. The blast wave travelled at 984 miles per hour in all directions, demolishing over two-thirds of Hiroshima's buildings. The heat from the explosion caused third-degree burns within a wide radius, and the pressure blast blew in windows and tipped over stoves.
The cloud's rapid ascent and massive size were not the only terrifying aspects of the explosion. The fireball reached a diameter of 900 feet, and temperatures on the ground soared to 7,000 degrees Fahrenheit, melting buildings and vaporizing human and animal tissue. The radiation released by the bomb claimed countless lives, with many succumbing to its effects within a week.
The aftermath of the bombing was captured in a rare photograph discovered in a former Japanese elementary school. This image, taken from Kaitaichi, six miles east of Hiroshima's centre, provides a glimpse of the distinct two-tiered cloud formed by the explosion. It serves as a stark reminder of the devastation wrought by the atomic bomb, which claimed the lives of between 150,000 and 246,000 people, most of whom were civilians.
The Hiroshima bombing, along with the subsequent Nagasaki bombing, remain the only uses of nuclear weapons in armed conflict. The immense destruction and loss of life they caused ushered in a new era of warfare, where the potential for catastrophic destruction on a massive scale loomed over the world. The mushroom cloud that rose over Hiroshima symbolised the unprecedented power of nuclear technology and the profound impact it would have on humanity's future.
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The fireball reached 900 feet in diameter
On August 6, 1945, at 8:16 a.m., the world's first atomic bomb attack took place over Hiroshima, Japan. The uranium bomb, nicknamed "Little Boy", was dropped from the B-29 Superfortress "Enola Gay" at an altitude of 31,060 feet (9,467 m).
One second after the detonation, the fireball reached its maximum size of 900 feet (274.32 m) in diameter. The extreme heat and pressure generated by the explosion caused the air to behave like a fluid, with the less dense, expanding fireball rising rapidly through the atmosphere. This upward movement of hot air created a spherical cap bubble, similar to the principle behind a hot-air balloon.
As the fireball ascended, it cooled and condensed, forming the distinctive mushroom cloud shape. The rising column of hot air drew cooler air from the surrounding area, creating strong "afterwinds" that fed the growing cloud. This process resulted in the formation of a Rayleigh-Taylor instability, where the boundary between the hot, buoyant gases and the cooler surrounding air became unstable, leading to the characteristic two-tiered structure of the mushroom cloud.
The mushroom cloud over Hiroshima rose to an altitude of over 60,000 feet in about ten minutes. The Enola Gay, which had been circling at 30,000 feet about 30 seconds after the explosion, soon found itself beneath the towering cloud. The city of Hiroshima was engulfed in thick black smoke, with over two-thirds of its buildings demolished by the blast wave.
The immense size of the fireball and the subsequent formation of the mushroom cloud were testament to the unprecedented power of the atomic bomb. The blast wave travelled at 984 miles per hour (1,583.59 km/h) in all directions, vapourising human and animal tissue, melting buildings, and causing widespread destruction. The effects of the bomb extended beyond the immediate blast radius, with radiation and heat affecting a wide area.
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The blast wave travelled at 984 mph
On August 6, 1945, at 8:16 a.m., the world's first atomic bomb attack took place over Hiroshima, Japan. The blast wave travelled at 984 miles per hour, demolishing over two-thirds of Hiroshima's buildings in a massive, expanding firestorm. The bomb, nicknamed "Little Boy," detonated at a height of about 1,900 feet above the city.
The blast wave's incredible speed of 984 miles per hour was due to the immense energy released by the atomic bomb. This energy propagated outwards in all directions, creating a shockwave of compressed air that travelled at supersonic speeds. The force of the blast wave was so powerful that it destroyed buildings, uprooted trees, and threw people and debris into the air. Windows shattered, and stoves used for cooking breakfast were tipped over.
The blast wave was responsible for a significant portion of the destruction caused by the atomic bomb. It created a massive firestorm that swept through the city, igniting buildings, and fuel sources, leading to a conflagration that added to the devastation. The intense heat generated by the blast wave also contributed to the widespread fires that engulfed Hiroshima.
The speed and force of the blast wave instantly killed or grievously wounded 80,000 people. Many of those closest to the hypocenter were vaporized by the intense heat and radiation released by the bomb. Others further away but still within the blast radius suffered horrific injuries, including severe burns and trauma from flying debris. The blast wave's impact extended beyond physical structures and human lives; it also ignited fires that raged across the city, further exacerbating the devastation.
The effects of the blast wave extended beyond the initial detonation. In the aftermath of the explosion, a "'black rain' fell about one to two hours later. This rain was a tarry combination of ash, radioactive fallout, and water, causing severe radiation burns to those exposed. The blast wave also generated a massive mushroom cloud that rose to over 60,000 feet in about ten minutes. This cloud, visible from miles away, was a stark testament to the power of the atomic bomb.
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The Enola Gay was 11.5 miles away
On August 6, 1945, the Enola Gay, a B-29 Superfortress, dropped an atomic bomb on Hiroshima, Japan. The Little Boy bomb was released from 31,060 feet (9,467 metres) and fell for approximately 53 seconds before detonating at a height of 1,968 feet (600 metres) above the city. The Enola Gay travelled 11.5 miles (18.5 kilometres) before it felt the shockwaves from the blast.
The Enola Gay was flown by Colonel Paul W. Tibbets Jr. and accompanied by two other B-29s: The Great Artiste, which carried instrumentation, and a then-nameless aircraft later called Necessary Evil, commanded by Captain George Marquardt, which took photographs. The crew of the Enola Gay consisted of 12 men, including Captain Robert A. Lewis, the regularly assigned aircraft commander, and Captain William S. "Deak" Parsons, the weaponeer and mission commander.
The detonation of Little Boy created a massive, expanding firestorm that demolished over two-thirds of Hiroshima's buildings. The blast wave travelled at 984 miles per hour (1,583.59 kilometres per hour) in all directions, reaching temperatures of 7,000 degrees Fahrenheit (3,871 Celsius). The fireball reached a maximum diameter of 900 feet (274.32 metres) before the mushroom cloud began to form. About 30 seconds after the explosion, the Enola Gay circled back and rose to 30,000 feet, but the mushroom cloud had already risen above them.
The Enola Gay returned safely to its base on Tinian, touching down after 12 hours and 13 minutes. The crew of the Enola Gay was greeted by several hundred people, including journalists and photographers, and Tibbets was presented with the Distinguished Service Cross on the spot. The Hiroshima mission was the first nuclear bombing mission, with Kokura and Nagasaki as alternative targets.
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The 'black rain' fell one to two hours later
On the morning of 6 August 1945, the US dropped an atomic bomb on Hiroshima, Japan. The blast instantly killed or grievously wounded 80,000 people, and over 100,000 more died from its effects in the following months. The bomb left devastation in its wake, with two-thirds of Hiroshima's buildings demolished and the city engulfed in a thick black smoke.
The black rain that fell one to two hours after the detonation was a direct result of the mushroom cloud formed by the explosion. The cloud, which rose to over 60,000 feet in about ten minutes, was composed of three types of clouds produced by the bomb. Firstly, the blast stirred up soil and dust, which were carried upwards by rising air currents heated by the fireball, forming the column or pillar of the mushroom cloud. This cloud rose to 4000 meters. Secondly, the cloud spread out, forming the cap of the mushroom shape. As it spread, the temperature and pressure decreased, causing water vapour in the air to condense into droplets. Finally, the third cloud was caused by the huge fires started by the heat of the bomb.
The black rain fell on a clear day, with the local weather station reporting that the morning was "clear and windless, almost completely calm". The rain was a result of the mushroom cloud, with the blast creating a cloud of soil and dust that rose into the sky and formed the column of the mushroom shape. This cloud contained radioactive fallout, which contaminated the rain. The rain fell in areas outside the city centre, with one resident of Yuki town, northwest of Hiroshima, recalling that her "white blouse turned black" from the rain.
The effects of the black rain were not fully understood at the time, but in 1976, the Japanese government offered health check-ups to people who lived in areas where heavy black rain had fallen. This decision was made in recognition of the potential health impacts of exposure to the radioactive rain. The city of Hiroshima also plans to survey 30,000 citizens who have lived in the city since 1945 to study the psychological effects of exposure to the black rain.
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Frequently asked questions
The cloud rose to over 60,000 feet in about ten minutes.
The bombing took place on 6 August 1945, at 8:16 am.
The bombing killed between 150,000 and 246,000 people, most of whom were civilians.
The aircraft was called the Enola Gay.
The bomb was called "Little Boy".
