Emma Wilson
Mushroom clouds are distinctive mushroom-shaped clouds that form after a large explosion. They are most commonly associated with nuclear explosions, but any sufficiently energetic detonation or deflagration will produce a similar effect. The clouds are formed by the sudden formation of a large volume of lower-density gases at any altitude, causing a Rayleigh-Taylor instability. The cloud reaches its maximum height after about 10 minutes and may continue to be visible for about an hour or more before being dispersed by the wind. The brightness of the glow decreases rapidly with elapsed time since the detonation, becoming barely visible after a few tens of seconds. The distance from which a mushroom cloud is visible depends on various factors such as the size of the explosion, the height of the burst, and atmospheric conditions.
| Characteristics | Values |
|---|---|
| Height | 20,000 feet |
| Time to reach maximum height | 10 minutes |
| Visibility duration | 1 hour or more |
| Colour | Red or reddish brown initially, changing to white |
| Composition | Solid particles of weapon debris, small drops of water, dirt, and debris |
| Shape | Mushroom-shaped |
| Cause | Nuclear explosion, powerful conventional weapons, volcanic eruptions, impact events |
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What You'll Learn
What causes a mushroom cloud?
A mushroom cloud is the result of a large explosion, often associated with a nuclear explosion. However, any sufficiently energetic detonation or deflagration will produce a similar effect. They can be caused by powerful conventional weapons, including large thermobaric weapons. Some volcanic eruptions and impact events can also produce natural mushroom clouds.
Mushroom clouds are the result of the sudden formation of a large volume of lower-density gases at any altitude, causing a Rayleigh-Taylor instability. The buoyant mass of gas rises rapidly, resulting in turbulent vortices curling downward around its edges. This forms 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 explosion initially expands in a spherical shape, but as it rises, the hot air is cooled by energy radiation, and the shape changes from a sphere to a violently rotating spheroidal vortex. The speed of rotation slows as the fireball cools and may stop entirely during later phases. The vapors condense to form a cloud containing solid particles of weapon debris and small drops of water derived from the air sucked into the rising fireball. The cloud continues to rise and flatten, forming the rounded cap of the mushroom.
The height reached by the mushroom cloud depends on the heat energy of the explosion and the atmospheric conditions. If the cloud reaches the tropopause, it will tend to spread out. However, if there is sufficient energy remaining, a portion of the cloud will ascend into the more stable air of the stratosphere. The cloud attains its maximum height after about 10 minutes and is then said to be "stabilized". It continues to grow laterally, producing the characteristic mushroom shape. The cloud may persist in the atmosphere for about an hour before being dispersed by winds and merging with natural clouds in the sky.
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How long is a mushroom cloud visible for?
A mushroom cloud is the result of a thermonuclear explosion, or any massive release of heat, such as from a volcano or a large explosion. The iconic cloud shape is formed when a large volume of lower-density gases is suddenly released at high altitudes, causing a Rayleigh-Taylor instability. The mass of gas rises rapidly, forming turbulent vortices that curl downwards around its edges, creating a vortex ring that draws up a central column of smoke, debris, condensed water vapour, or a combination of these elements. This forms the "'stem" of the mushroom cloud.
The brightness of the glow surrounding the head of the mushroom cloud decreases rapidly, becoming barely visible after a few tens of seconds. The cloud reaches its maximum height after about 10 minutes and is then considered "stabilized". It continues to grow laterally, producing the characteristic mushroom shape. The cloud may persist for about an hour or more before being dispersed by the wind and merging with other natural clouds in the sky. The fallout may appear as dry, ash-like flakes, or as particles too small to be visible, deposited by rain.
The colour of the cloud is initially red or reddish-brown due to the presence of nitrous acid and oxides of nitrogen. As the fireball cools and condensation occurs, the colour changes to white, mainly 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 carried up by the afterwinds.
The fallout from a nuclear explosion can pose long-term hazards due to the presence of residual radiation from long half-life fission products such as Sr-90 and Cs-137. Within 24 hours after the burst, the fallout gamma radiation level drops significantly, but the primary fallout hazard is gamma radiation from short-lived radioisotopes, which represent the bulk of the activity.
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What does a mushroom cloud look like?
A mushroom cloud is a distinctive mushroom-shaped 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 large thermobaric weapons. Some volcanic eruptions and impact events can produce natural mushroom clouds.
Mushroom clouds result from the sudden formation of a large volume of lower-density gases 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 the "stem" of the mushroom cloud, and it may contain smoke, debris, condensed water vapour, or a combination of these.
The initial colour of some radioactive clouds can be red or reddish-brown, due to the presence of nitrogen dioxide and nitric acid, formed from initially ionised nitrogen, oxygen, and atmospheric moisture. In the high-temperature, high-radiation environment of the blast, ozone is also formed. The reddish hue is later obscured by the white colour of water/ice clouds, the dark colour of smoke and debris, and the condensation of the fast-flowing air as the fireball cools. The ozone gives the blast its characteristic corona discharge-like smell.
The intense radiation in the first seconds after the blast may cause an observable aura of fluorescence—a blue-violet-purple glow of ionized oxygen and nitrogen out to a significant distance from the fireball, surrounding the head of the forming mushroom cloud. This light is most easily visible at night or under conditions of weak daylight. The brightness of the glow decreases rapidly with elapsed time since the detonation, becoming barely visible after a few tens of seconds. Nuclear mushroom clouds are often accompanied by short-lived vapour clouds, known as "Wilson clouds", condensation clouds, or vapour rings.
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Are there natural mushroom clouds?
Mushroom clouds are most commonly associated with nuclear explosions. They are formed by the sudden release of a large volume of lower-density gases at high altitudes, 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 of smoke, debris, and condensed water vapour to create the iconic "mushroom stem".
However, mushroom clouds are not exclusive to nuclear explosions. They can also occur naturally through powerful volcanic eruptions and impact events, such as the collision of large meteorites with the Earth. In 1798, Gerhard Vieth published an illustrated account of a cloud in the neighbourhood of Gotha, Germany, that resembled a mushroom in shape. This cloud was interpreted as an irregular meteorological phenomenon and was believed to have caused a storm with rain and thunder.
Volcanoes, in particular, can create mushroom-shaped plumes that closely resemble those produced by nuclear blasts. The 1980 eruption of Mount St. Helens generated a massive mushroom cloud visible for miles. The cloud comprised ash, rock, and steam, and its shape depended on the volcano's contents and the nature of its eruption. Some volcanic mushroom clouds are tall and skinny, while others are short and wide.
While less common, certain meteorological phenomena can also create mushroom-like shapes. Supercell storms, for instance, can sometimes generate clouds that resemble mushroom clouds. These storms, which are the strongest type of thunderstorm and are capable of producing tornadoes, can form clouds that reach heights of 55,000 to 70,000 feet. If the updraft is strong and narrow enough, it can resemble a mushroom cloud, as observed in the case of the "Doomsday" cloud over Siberia.
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How high can a mushroom cloud get?
A 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. The height of a mushroom cloud depends on several factors, including the size and yield of the explosion, the altitude of the detonation, and the environmental conditions present at the time.
In general, the height of a mushroom cloud is influenced by the amount of energy released during the explosion, which creates a buoyant mass of gas that rises rapidly. The ascent continues until the mass of hot gases reaches its equilibrium level, at which point the cloud begins to flatten and take on the characteristic mushroom shape. The larger and more energetic the explosion, the greater the volume of lower-density gases produced, and the higher the cloud will rise.
The highest a mushroom cloud can get is influenced by the altitude of the detonation. A detonation that occurs high above the ground may produce a mushroom cloud without a stem, as the ground acts as a backstop for the blast to push against. At very high altitudes, the lower air density allows the hot gases to expand more easily in all directions, resulting in a more spherical cloud shape.
The environmental conditions, such as air pressure, temperature, and humidity, also play a role in determining the height of a mushroom cloud. Higher-yield explosions cause intense updrafts, where air speeds can reach 300 miles per hour (480 km/h). The entrainment of higher-humidity air, combined with the associated drop in pressure and temperature, contributes to the formation of the characteristic stem and cap of the mushroom cloud.
The largest 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. This massive cloud was the result of an extremely powerful explosion, equivalent to around 50 megatons of TNT.
In summary, the height of a mushroom cloud depends on various factors, including the size and yield of the explosion, the altitude of the detonation, and the surrounding environmental conditions. The interplay between these factors determines how high a mushroom cloud can rise before it stabilizes and begins to dissipate.
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Frequently asked questions
A mushroom cloud can be seen from up to 5.6 km away, as observed from a tower on Bikini Island after the underwater Baker nuclear explosion in 1946. The cloud may continue to be visible for about an hour or more before being dispersed by the wind.
A mushroom cloud forms due to the sudden creation of a large volume of lower-density gases at high altitudes, causing a Rayleigh-Taylor instability. The mass of hot gases rises rapidly, resulting in 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 to form the "stem".
The colour of the cloud is initially red or reddish-brown due to the presence of nitrous acid and oxides of nitrogen. As the fireball cools and condensation occurs, the colour changes to white, mainly due to the formation of water droplets.
No, although the effect is most commonly associated with nuclear explosions, any sufficiently energetic detonation or deflagration can produce a similar effect. Powerful conventional weapons, large thermobaric weapons, some volcanic eruptions, and impact events can also create natural mushroom clouds.
A mushroom cloud reaches its maximum height in about 10 minutes, after which it stabilizes and continues to grow laterally to form the characteristic mushroom shape.
