Sarah Brown
Mushroom clouds are the result of a massive release of heat, such as a nuclear explosion, and are characterised by their distinctive mushroom shape. The effect is caused by the formation of a large volume of lower-density gases at any altitude, resulting in a Rayleigh-Taylor instability. The hot gas rises rapidly, creating turbulent vortices that curl downward, forming a temporary vortex ring that draws up a central column of smoke, debris, condensed water vapour, or a combination of these elements. The initial colour of the cloud is reddish-brown due to the presence of nitrogen dioxide and nitric acid, but as the fireball cools, it turns white due to the condensation of water droplets. The cloud continues to rise and stabilise, eventually reaching its maximum height and forming the rounded cap of the mushroom.
| Characteristics | Values |
|---|---|
| Formation | Mushroom clouds are formed by large explosions, particularly nuclear explosions. They can also be caused by powerful conventional weapons, volcanic eruptions, and impact events. |
| Appearance | The cloud is characterized by a mushroom-like shape, with a rounded cap and a central column or stem. The stem is formed by the upward movement of smoke, debris, and condensed water vapor. |
| Color | Initially, the cloud is 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. |
| Height | The cloud reaches its maximum height in about 10 minutes and is considered stabilized. It may continue to grow laterally, persisting in the atmosphere for about an hour before being dispersed by winds. |
| Phases of Formation | Early time (first ~20 seconds): fireball formation and mixing of fission products with ground material. Rise and stabilization phase (20 seconds to 10 minutes): hot gases rise, and early large fallout occurs. Late time (until ~2 days later): airborne particles are distributed by wind, gravity, and precipitation. |
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What You'll Learn
Any large explosion can form a mushroom cloud
Mushroom clouds are most commonly associated with nuclear explosions. However, any sufficiently energetic detonation or deflagration will produce a similar effect. This means that any large explosion can form a mushroom cloud.
Mushroom clouds can be caused by powerful conventional weapons, including thermobaric weapons such as the ATBIP and GBU-43/B MOAB. They can also be formed by natural events, such as volcanic eruptions or impact events. For example, an artist in 1782 painted an image of what seemed to be a massive explosion resembling a mushroom cloud during the Franco-Spanish attack on Gibraltar.
Mushroom clouds are formed by the sudden creation of a large volume of lower-density gases at any altitude, resulting in Rayleigh-Taylor instability. The buoyant mass of gas rises rapidly, forming turbulent vortices that curl downward around its edges. This creates a temporary vortex ring that draws up a central column of smoke, debris, condensed water vapour, or a combination of these elements to form the "mushroom stem".
The formation of a mushroom cloud occurs in several phases. Initially, a fireball forms, and fission products mix with the material aspirated from the ground or ejected from the crater. This is followed by the rise and stabilization phase, where hot gases rise, and early large fallout is deposited. Finally, the late-time phase occurs, where airborne particles are distributed by wind, deposited by gravity, or scavenged by precipitation. The shape of the cloud is influenced by local atmospheric conditions and wind patterns.
The height and appearance of a mushroom cloud depend on the explosive yield of the bomb and the altitude of the detonation. When a bomb explodes, energy is released in all directions, initially forming a sphere of hot air. However, due to buoyancy, the middle column of the sphere rises faster, creating a vacuum that draws in smoke and debris, forming the characteristic mushroom shape.
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The explosion must occur under Earth's gravity
The formation of a mushroom cloud is dependent on Earth's gravity. The explosion must occur under Earth's gravity for the cloud to take its distinctive mushroom shape. This is because, without gravity, the explosive's by-product gases would remain spherical. Under Earth's gravity, a large volume of lower-density gases is formed at any altitude, causing a Rayleigh-Taylor instability. 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. This central column is made up of smoke, debris, condensed water vapour, or a combination of these, forming the "mushroom stem".
The stem of the mushroom cloud is formed when the detonation altitude is low enough for afterwinds to draw in dirt and debris from the ground below. The ascent of the gases stops once it reaches its equilibrium level, and the cloud begins to flatten into the characteristic mushroom shape, often assisted by surface growth from decaying turbulence.
The mushroom cloud can be created by any massive release of heat, such as a nuclear explosion, a volcanic eruption, or a large conventional explosion. Nuclear weapons are usually detonated above the ground to maximise the effect of their spherically expanding fireball and blast wave. The fireball, a hot, bright spherical mass of air and gas, rises through the atmosphere, creating a vacuum in its wake. This vacuum is immediately filled with smoke and debris, forming the central column of what will become the mushroom cloud.
The fireball continues to rise and soon reaches a point in the atmosphere where the air is dense enough to slow its ascent. The weight and density of the air flatten the fireball and its trailing smoke, causing it to widen and form the rounded cap of the mushroom. The cloud continues to rise as it flattens, and the upward movement and cooled fireball contribute to the formation of the mushroom cloud.
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The cloud is formed by smoke and debris
A mushroom cloud is formed by smoke and debris, 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 outcome. These explosions can be caused by powerful conventional weapons, including thermobaric weapons, or even natural events like volcanic eruptions.
The formation of a mushroom cloud can be understood in several phases. Initially, a fireball is formed, with fission products mixing with material from the ground or the surrounding environment. This fireball is a hot, bright spherical mass of air and gas, resulting from the release of electromagnetic radiation during a nuclear explosion. The condensation of evaporated ground particles occurs within the first few seconds, particularly when fireball temperatures are between 3500 and 4100 Kelvin.
As the fireball rises, it undergoes a transformation due to atmospheric friction and energy radiation. The bottom of the fireball is cooled first, causing it to change from a sphere to a rotating spheroidal vortex. This creates a Rayleigh-Taylor instability, leading to turbulence and the formation of a vortex that pulls in more air, generating strong "afterwinds."
The rising column of hot gases eventually reaches its equilibrium level, where the ascent stops. At this point, the cloud begins to flatten and expand laterally, forming the iconic mushroom shape. This flattening is facilitated by the weight and density of the cooler air at higher altitudes, which acts on the fireball similarly to how a hot air balloon rises and then flattens as it cools. The smoke and debris sucked into the updraft contribute to the dark colour of the mushroom cloud's stem.
The height and longevity of the mushroom cloud depend on the heat energy of the explosion and the atmospheric conditions. Under favourable conditions, the cloud can reach remarkable heights and remain visible for about an hour or more before being dispersed by winds and merging with natural clouds.
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The cloud's colour changes from reddish-brown to white
A mushroom cloud is the result of a massive release of heat, usually from a nuclear explosion, but it can also be formed by powerful conventional weapons or natural phenomena such as volcanic eruptions. The formation of a mushroom cloud occurs in several phases, with the initial reddish-brown colour of the cloud being one of the first distinctive features.
The reddish-brown hue is caused by the presence of nitrogen dioxide and nitric acid, formed from initially ionized nitrogen, oxygen, and atmospheric moisture. The reddish colour can also be attributed to the presence of nitrous acid and oxides of nitrogen, formed during the explosion. This initial reddish phase is followed by the rise and stabilization phase, where the hot gases rise and early large fallout is deposited.
As the fireball cools and condensation occurs, the reddish-brown colour begins to change. The cooling process is influenced by the local atmospheric conditions and wind patterns, which affect the distribution of the fallout. The characteristic reddish hue is gradually obscured by the formation of water/ice clouds, which have a white colour due to the condensation of water droplets.
The white colour of the cloud is a result of the same physical process that forms ordinary clouds. As the fireball continues to cool, the water vapour condenses into small droplets, giving the cloud its white appearance. This process is similar to the formation of clouds in the Earth's atmosphere through the condensation of water vapour.
Additionally, the mushroom cloud may also take on a dirty brown colour if the explosion occurs on the Earth's surface. In this case, debris and dirt are vaporized and sucked into the explosion, contributing to the brown colour. The brown colour can be observed below the white cloud, forming the stem and cap of the mushroom-shaped cloud.
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The cloud reaches its maximum height after 10 minutes
A mushroom cloud is formed by a massive release of heat from a large explosion. The explosion produces a fireball that rises through the atmosphere, creating a vacuum that is filled with smoke and debris, forming the central column of what will become the mushroom cloud. This is known as the "spherical cap bubble", which rises due to having lower-density gases at its core. As the fireball rises, it changes from a sphere to a violently rotating vortex due to Rayleigh-Taylor instability. This causes turbulence and a vortex that sucks in air, creating strong "afterwinds".
The initial colour of the cloud is reddish-brown due to the presence of nitrous acid and oxides of nitrogen. As the fireball cools, condensation occurs, and the colour changes to white due to the formation of water droplets. The cloud consists of small particles of radioactive fission products, weapon residues, water droplets, and larger particles of dirt and debris. The height reached by the cloud depends on the heat energy of the explosion and the atmospheric conditions.
After the explosion, the cloud enters the "rise and stabilization phase", which lasts from 20 seconds to 10 minutes. During this phase, the hot gases rise, and early large fallout is deposited. The cloud reaches its maximum height at the end of this phase, after about 10 minutes, and is said to be stabilized. It continues to expand laterally, forming the characteristic mushroom shape.
The cloud may remain visible for about an hour or more, depending on weather conditions, before being dispersed by winds and merging with natural clouds in the sky. The formation of a mushroom cloud is not limited to nuclear explosions, as any sufficiently energetic detonation or natural events such as volcanic eruptions can produce a similar effect.
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Frequently asked questions
A mushroom cloud is a cloud of debris, smoke, and condensed water vapour that forms after a large explosion. It is named so because of its mushroom-like shape.
A mushroom cloud is formed when a large volume of lower-density gases is formed at any altitude, causing a Rayleigh-Taylor instability. The buoyant mass of gas rises rapidly, forming a vortex that draws up a central column of smoke, debris, and condensed water vapour.
A mushroom cloud consists of small particles of radioactive fission products, weapon residues, water droplets, and larger particles of dirt and debris. The initial colour of the cloud is reddish-brown due to the presence of nitrogen dioxide and nitric acid. As the fireball cools, the colour changes to white due to the formation of water droplets.
Mushroom clouds are typically associated with nuclear explosions. However, they can also be caused by powerful conventional weapons, volcanic eruptions, and impact events. Any massive release of heat that produces a large explosion under Earth's gravity can form a mushroom cloud.
