Emily Johnson
The mushroom cloud shape that is synonymous with atomic explosions is caused by the physics of the blast. A nuclear explosion vaporises everything inside its fireball, including soil and water, which is carried upwards. This creates a mushroom cloud, which attains its maximum height after about 10 minutes. The upward flow of air after the explosion is what causes the mushroom cap to form. The blast also pushes almost all matter away, creating a vacuum that must collapse. The blast wave edge forms high-pressure air, and as the explosion dies down, this high pressure rushes back in to fill the vacuum. This pushes the mushroom cloud higher, forming the stem of the mushroom. The blast wind at sea level may exceed 1,000 km/h (600 mph; 300 m/s). The effects of a nuclear blast include severe burns, cancer, and death.
| Characteristics | Values |
|---|---|
| Height | The height of a mushroom cloud depends on the heat energy of the weapon and the atmospheric conditions. The mushroom cloud produced by the Tsar Bomba explosion extended 40 miles into the atmosphere, with a width of 60 miles at its apex and 25 miles at its base. The mushroom cloud over Nagasaki, Japan, was described as reaching a height of 45,000 feet. The mushroom cloud produced by the Hiroshima explosion in 1945 rose to more than 60,000 feet in 10 minutes and to a cruising altitude of 10,000 meters in 30 seconds. |
| Shape | Mushroom clouds are formed due to Rayleigh-Taylor instability, which occurs when a fluid of lower density pushes on a fluid of higher density, causing the interface between them to become unstable and resulting in the mushroom shape. |
| Color | The initial color of the cloud can be reddish-brown due to the presence of nitrogen dioxide and nitric acid. As the fireball cools, the color changes to white due to the formation of water droplets, similar to an ordinary cloud. |
| Composition | The cloud contains highly radioactive particles, primarily consisting of fission products and weapon debris aerosols. |
| Duration | A mushroom cloud may remain visible for about an hour or more before being dispersed by the wind and merging with natural clouds in the sky. |
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What You'll Learn
- The height of a mushroom cloud depends on the heat energy of the weapon and atmospheric conditions
- The cloud reaches its maximum height after about 10 minutes and is then considered stabilized
- The fireball from an H-bomb rises so high that it hits the tropopause
- The Tsar Bomba's mushroom cloud extended 40 miles into the atmosphere
- The atomic bomb cloud over Nagasaki rose to a total of 45,000 feet
The height of a mushroom cloud depends on the heat energy of the weapon and atmospheric conditions
The iconic mushroom cloud produced by an atomic bomb is a result of complex interactions between the heat energy of the weapon and atmospheric conditions. Within the first 30 seconds of the blast, the cloud can rise to a significant height, as evidenced by the cloud over Hiroshima in 1945, which surpassed the cruising altitude of the plane that dropped the bomb within half a minute. This rapid ascent is due to the Rayleigh-Taylor instability, where the hot detonation gases and heated air are propelled at high velocity into the colder air above, resulting in an unstable interface between the two fluids of different densities.
The height of the mushroom cloud is influenced by the heat energy of the weapon. As the fireball rises, it cools, and the vapors condense to form a cloud containing weapon debris and water droplets. The phase change releases latent heat, further heating the cloud and driving it to higher altitudes. The stabilization altitude, or the point at which the cloud stops rising, depends on the temperature and dew point profiles in the air. If the cloud reaches the tropopause, a boundary between the troposphere and the stratosphere, it tends to spread out laterally. However, if the cloud retains sufficient energy, a portion of it may continue ascending into the stratosphere.
Atmospheric conditions also play a crucial role in determining the height of the mushroom cloud. The updraft created by the explosion can generate "afterwinds," which pull dirt and debris from the Earth's surface into the cloud. The presence of moisture in the atmosphere can lead to the formation of nitrogen dioxide and nitric acid, resulting in the reddish hue initially observed in the cloud. As the fireball continues to cool, the color changes to white due to the condensation of water droplets.
The maximum height of the mushroom cloud is typically reached within about 10 minutes, after which it is considered "stabilized." However, it may remain visible for an hour or more before being dispersed by the wind and merging with natural clouds. The height of these clouds can be immense, with the atomic bomb cloud over Nagasaki reaching a height of 45,000 feet, and the Tsar Bomba test explosion producing a mushroom cloud over 37 miles (60 kilometers) high.
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The cloud reaches its maximum height after about 10 minutes and is then considered stabilized
Mushroom clouds are clouds of smoke and debris that form following an explosion. They are not unique to nuclear explosions, but the mushroom clouds produced by atomic bombs are particularly notable due to their enormous size. These clouds form due to the sudden release of a large volume of lower-density gases, which causes a Rayleigh-Taylor instability. This instability results in the upward curling of turbulent vortices, forming a temporary vortex ring that draws up a central column, which may include smoke, debris, condensed water vapour, or a combination of these elements, thus creating the iconic "mushroom stem".
The height of the mushroom cloud is influenced by the heat energy of the weapon and the atmospheric conditions. The cloud continues to rise until it reaches an altitude where it is no longer of lower density than the surrounding air, at which point it stabilises and begins to disperse. This stabilisation phase typically occurs within the first 10 minutes after the explosion, and the cloud may continue to grow laterally, forming the characteristic mushroom shape.
The speed at which the cloud rises slows down over time. For example, the mushroom cloud that formed after the Hiroshima bombing in 1945 rose to over 60,000 feet within the first 10 minutes, with an initial upward expansion of 333 m/s that slowed to an average of 100 m/s after the first 10 minutes. The height of this cloud can be contrasted with that of the atomic bomb detonated over Nagasaki, which reached a total height of 45,000 feet.
The highest mushroom cloud ever produced by a nuclear detonation was the Tsar Bomba, which extended 40 miles into the atmosphere, with a width of 60 miles at its apex and 25 miles at its base. While the height of a mushroom cloud is impressive, it is important to note that the smallest particles within the cloud can reach the stratosphere and remain there for extended periods, posing potential hazards.
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The fireball from an H-bomb rises so high that it hits the tropopause
The fireball from an H-bomb rises rapidly, creating a powerful updraft that is filled by the surrounding air and dust. This fireball is an extremely hot and highly luminous spherical mass of air and gaseous weapon residues, which occurs within less than one millionth of a second of the weapon's detonation. It is tens of millions of degrees, as hot as the interior of the sun, and causes the complete disintegration of molecules and atoms.
The fireball rises very quickly, expanding spherically from the centre. It is initially formed by gamma rays from the nuclear processes preceding the explosion, which superheat the surrounding air and material. The majority of the energy that forms the fireball is in the soft X-ray region of the electromagnetic spectrum, produced by the inelastic collisions of high-speed fission and fusion products.
The mushroom clouds can rise to tens of thousands of feet in minutes. In Hiroshima in 1945, the mushroom cloud rose to more than 60,000 feet within the first 10 minutes. Within the first 30 seconds, it had risen 10,000 meters, which was over the cruising altitude of the plane that dropped the bomb.
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The Tsar Bomba's mushroom cloud extended 40 miles into the atmosphere
The Tsar Bomba was a Soviet thermonuclear bomb, and the largest nuclear weapon ever detonated. It was exploded over Novaya Zemlya Island in the Arctic Ocean on 30 October 1961 and produced the most powerful human-made explosion ever recorded. The Tsar Bomba mushroom cloud extended 40 miles into the atmosphere, seven times higher than Mount Everest. The cloud was about 67 km (42 mi) high, or 60 km (37 mi) high according to another source. The top of the cloud had a width of 59 miles (95 km) and the base a width of 25 miles (43 km). The Tsar Bomba mushroom cloud was visible 800 km (500 mi) from the explosion site.
The Tsar Bomba explosion was an ultra-high-power low-air nuclear explosion. The flare was visible at a distance of more than 1,000 km (620 mi) and was observed in Norway, Greenland, and Alaska. The blast wave circled the globe three times, with the first circuit taking 36 hours and 27 minutes.
The bomb was set to detonate at 13,000 feet and was dropped from a height of 34,000 feet. It exploded about 2.5 miles (4 km) above the ground, producing a mushroom cloud. The resulting damage was massive. Severny, an uninhabited village 34 miles (55 km) from ground zero, was levelled, and buildings more than 100 miles (160 km) away were reportedly damaged. It is estimated that the heat from the blast would have caused third-degree burns up to 62 miles (100 km) distant.
The Tsar Bomba was a three-stage hydrogen bomb with a final design by Soviet physicist Andrei Sakharov. The weapon weighed 27 tons, with a length of 26 feet (8 metres) and a diameter of about 7 feet (2 metres). The Tsar Bomba yielded approximately 50 megatons of TNT, though initial data suggested a yield of 58.6 Mt. The bomb was a modification of an earlier project, RN202, and was ordered by Nikita Khrushchev as a show of strength in response to America's nuclear weapons possessions.
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The atomic bomb cloud over Nagasaki rose to a total of 45,000 feet
Mushroom clouds are distinctive mushroom-shaped clouds of debris, smoke, and condensed water vapour that form after large explosions. They are most commonly associated with nuclear explosions, but any sufficiently energetic detonation or deflagration will produce a similar effect. Nuclear weapons are usually detonated above the ground to maximize the effect of their spherically expanding fireball and blast wave.
The formation of a mushroom cloud is due to the sudden release of large amounts of energy, creating a very hot bubble of gas that interacts with the cooler surrounding air, making it less dense. This hot fireball rises very rapidly, creating a powerful updraft that is then filled by the surrounding air and dust, forming the cloud. The buoyant mass of gas rises rapidly, resulting in turbulent vortices curling downward around its edges, forming a temporary vortex ring that draws up a central column, possibly with smoke, debris, condensed water vapour, or a combination of these, to form the "mushroom stem".
The eventual height reached by the cloud depends on the heat energy of the weapon and the atmospheric conditions. The cloud continues to rise until it reaches an altitude where it is no longer of lower density than the surrounding air; at this point, it stabilizes and begins to disperse, drifting back down, resulting in fallout. In the case of nuclear explosions, this stabilization altitude is rather high in the atmosphere, normally in the ozone layer or the tropopause, the boundary between the troposphere and the stratosphere. The cloud attains its maximum height after about 10 minutes and continues to grow laterally to produce the characteristic mushroom shape.
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Frequently asked questions
Mushroom clouds can rise to tens of thousands of feet in minutes. The highest recorded mushroom cloud was produced by the Tsar Bomba, which extended 40 miles into the atmosphere.
Mushroom clouds are caused by Rayleigh-Taylor instability, which occurs when a fluid of lower density pushes onto a fluid of higher density. This results in the interface between the two fluids becoming unstable and any small irregularity at the interface growing larger.
The eventual height of a mushroom cloud depends on the heat energy of the weapon and atmospheric conditions. If the cloud reaches the tropopause, it tends to spread out. However, if there is sufficient energy remaining, a portion of the cloud will enter the stratosphere.
A mushroom cloud typically reaches its maximum height in about 10 minutes, after which it is considered stabilized. It will continue to grow laterally, producing the characteristic mushroom shape.
No, mushroom clouds are not unique to atomic explosions. Any large explosion can produce a mushroom cloud, and they can also be observed in everyday phenomena, such as pouring milk into coffee.
