John Miller
A mushroom cloud is a distinctive mushroom-shaped cloud of debris, smoke, condensed water vapour, and radioactive fission products resulting from a large explosion. They are most commonly associated with nuclear explosions, but any sufficiently energetic detonation or deflagration can produce a similar effect. Mushroom clouds can also be caused by powerful conventional weapons, volcanic eruptions, or impact events. The formation of a mushroom cloud undergoes several phases, from the initial fireball and fission to the rise and stabilization phase, and finally, the distribution of airborne particles by wind, gravity, and precipitation.
| Characteristics | Values |
|---|---|
| Definition | A distinctive mushroom-shaped flammagenitus cloud of debris, smoke, and usually condensed water vapour resulting from a large explosion |
| Formation | A mushroom cloud can be created from any massive release of heat, especially a nuclear explosion |
| Colour | The cloud is initially red or reddish-brown, due to the presence of nitrous acid and oxides of nitrogen. It then turns white, due to the water droplets |
| Composition | Small particles of radioactive fission products and weapon residues, water droplets, and larger particles of dirt and debris |
| Duration | Depending on weather conditions, a mushroom cloud can persist in the atmosphere for about an hour until winds and air currents disperse it |
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What You'll Learn
Formation
A mushroom cloud is a distinctive mushroom-shaped cloud that is often associated with nuclear explosions. However, it is important to note that mushroom clouds can also be formed by other types of large explosions or even natural events such as volcanic eruptions.
The formation of a mushroom cloud involves several distinct phases. In the early moments of an explosion, a fireball forms, and fission products mix with material aspirated from the ground or ejected from the crater. This initial phase typically lasts around 20 seconds, with the condensation of evaporated ground occurring most intensely during fireball temperatures between 3500 and 4100 Kelvin.
As the fireball rises, it creates a vacuum, which is immediately filled with smoke, debris, and condensed water vapour, forming the visible central column of what will become the mushroom cloud. The colour of the cloud at this stage is typically red or reddish-brown due to the presence of nitrous acid and oxides of nitrogen.
During the rise and stabilization phase, which can last from 20 seconds to 10 minutes, the hot gases continue to rise, and early large fallout is deposited. The fireball increases in size and cools, and the vapours condense to form a cloud containing solid particles of weapon debris and small water droplets derived from the air sucked into the rising fireball. The cloud's shape is influenced by local atmospheric conditions and wind patterns.
In the late-time phase, which can last until about two days after the explosion, the airborne particles are distributed by the wind, deposited by gravity, or scavenged by precipitation. The mushroom cloud can persist in the atmosphere for about an hour until winds and air currents disperse it.
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Composition
A mushroom cloud is a distinctive mushroom-shaped cloud of debris, smoke, and usually condensed water vapour resulting from a large explosion. They are best known for their appearance after nuclear detonations, but any sufficiently energetic explosion or deflagration will produce a similar effect. They can be caused by powerful conventional weapons, including thermobaric weapons, or by natural events such as volcanic eruptions.
The formation of a mushroom cloud is due to 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. This draws up a central column of smoke, debris, condensed water vapour, or a combination of these, to form the "mushroom 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 water droplets.
The cloud continues to rise and flatten, forming the rounded cap of the mushroom. The ascent stops once the mass of hot gases reaches its equilibrium level, and the cloud begins to flatten into the characteristic mushroom shape, often assisted by surface growth from decaying turbulence. The height reached by the cloud depends on the heat energy of the explosion and the atmospheric conditions. If the cloud reaches the tropopause, about 6-8 miles above the Earth's surface, it will spread out. If there is sufficient energy remaining, a portion of the cloud will ascend into the more stable air of the stratosphere.
The mushroom cloud shape can also be formed by supercell storm clouds, which can swirl as high as 55,000 to 70,000 feet above the ground and are topped by a spreading cloud mass called an anvil. If the updraft is strong and narrow enough, it can resemble a mushroom cloud.
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Causes
Cloud mushrooms, also known as clump-forming mushrooms or multiceps mushrooms, are a type of fungus that gets their name from their distinctive cloud-like appearance. This unique look is caused by the dense clustering of their fruit bodies, which often form large, fluffy masses. These mushrooms are characterized by their ability to form multiple, interconnected fruit bodies that grow and fuse together, creating a cloudy or cotton-like mass. While there are several species of cloud mushrooms, one of the most common is Multiceps multiceps, which is widely distributed across various regions. Now, let's delve into the causes that contribute to the formation and characteristics of these fascinating fungi:
Cause: Genetic Predisposition
The distinctive characteristics of cloud mushrooms can be attributed to their genetic makeup. These fungi possess a unique genetic predisposition that encourages the formation of multiple, closely spaced fruit bodies. This genetic trait is responsible for the dense clustering that gives cloud mushrooms their signature appearance. The genes regulate the development of the mushroom's mycelium, promoting the growth of multiple primordia (initial mushroom structures) in close proximity.
Cause: Dense Mycelial Growth
The mycelium, which is the vegetative part of the fungus, exhibits dense and vigorous growth. The mycelial strands grow closely packed together, forming a thick, intertwined network. This dense mycelial growth provides the structural foundation for the formation of multiple fruit bodies in close proximity. The intertwined mycelium allows for the exchange of nutrients and signals between the developing mushrooms, influencing their coordinated growth and fusion.
Cause: Environmental Conditions
Environmental factors play a crucial role in triggering the fruiting process in cloud mushrooms. These fungi typically fruit in response to specific ecological stimuli. For example, changes in temperature, moisture levels, and nutrient availability can induce the mycelium to form primordial and subsequent fruit bodies. Optimal conditions, such as moist, humid environments with adequate nutrient sources, further promote the vigorous growth and fusion of multiple fruit bodies.
Cause: Nutrient Availability and Competition
Cloud mushrooms often thrive in nutrient-rich environments, particularly those with abundant organic matter. The presence of sufficient nutrients encourages the vigorous growth of multiple fruit bodies. Additionally, there may be an element of competition at play. In dense clusters, individual mushrooms compete for resources, light, and space. This competitive environment could contribute to the dense clustering and upward growth of the fruit bodies as they strive for access to essential resources.
Cause: Hormonal and Chemical Signals
Chemical and hormonal signals within the fungus also influence the formation of cloud mushrooms. These signals are involved in coordinating the growth and development of the fruit bodies. Certain chemicals and hormones may promote the clustering of primordia and regulate the fusion process. The exchange of these signals between nearby mushrooms in the dense cluster further enhances their coordinated growth and the characteristic cloud-like appearance.
These causes, influenced by genetics, environmental triggers, and physiological processes, contribute to the unique characteristics and formation of cloud mushrooms. Understanding these factors provides insight into the fascinating world of these clump-forming fungi and their ability to create distinctive cloudy masses in nature.
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Phases
A mushroom cloud is a distinctive mushroom-shaped cloud that is the result of a large explosion. While mushroom clouds are best known for their appearance after nuclear explosions, they can also be caused by powerful conventional weapons or natural events such as volcanic eruptions.
The formation of a mushroom cloud occurs in several distinct phases:
Early Time
The first phase begins with the formation of a fireball, which occurs within the first 20 seconds. During this initial phase, fission products mix with material aspirated from the ground or ejected from a crater, and the evaporation of the ground occurs. This evaporation is most intense during fireball temperatures between 3500 and 4100 K.
Rise and Stabilization
The second phase lasts from 20 seconds to 10 minutes and is characterized by the rise of hot gases and the deposition of early large fallout. The fireball increases in size and cools, leading to the condensation of vapors and the formation of a cloud. This cloud contains solid particles of weapon debris and small water droplets derived from the air sucked into the rising fireball. The color of the cloud is initially red or reddish-brown due to the presence of nitrous acid and oxides of nitrogen.
Late Time
The final phase occurs until about two days later, during which the airborne particles are distributed by wind, deposited by gravity, or scavenged by precipitation. The shape of the cloud during this phase is influenced by local atmospheric conditions and wind patterns. The fallout distribution is typically a downwind plume, but if the cloud reaches the tropopause, it may spread against the wind due to its higher convection speed.
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History
The mushroom cloud is best known for its appearance after nuclear detonations. However, the term "mushroom cloud" was coined in the early 1950s, and mushroom clouds generated by non-nuclear explosions were being described centuries before the Atomic Age. For example, an aquatint by an unknown artist depicted the 1782 Franco-Spanish attack on Gibraltar, showing one of the attacking force's floating batteries exploding with a mushroom cloud. In 1798, Gerhard Vieth published an illustrated account of a cloud in the neighbourhood of Gotha that was "not unlike a mushroom in shape".
The first images of the atomic bomb that were widely circulated in the United States did not place the technology within clear visual paradigms. An aerial image of the Nagasaki mushroom cloud, taken just 15 minutes after the blast, was grainy, off-centre, and devoid of context. It failed to convey the scale of the destruction incurred on the ground beneath it. However, photographs of nuclear tests in the following years were assimilated into a visual network of American domesticity, technological spectatorship, and reverence for nature.
The atomic bombings of Hiroshima and Nagasaki in 1945 produced two of the most infamous mushroom clouds in history. These clouds rose miles into the sky and were visible from great distances. The Nagasaki mushroom cloud was photographed just 15 minutes after the blast, showcasing the terrible power of nuclear weapons. After World War II, many countries tested nuclear bombs, and scientists used these tests to study nuclear explosions and their effects.
The Trinity test, the first-ever nuclear test, represented the first moment in history when human activity came to be on equal terms with natural phenomena. The force from the explosion shattered windowpanes in Silver City, 180 miles away, and its radioactive fallout travelled as far as Indiana. The mushroom cloud from the Trinity test rose more than seven and a half miles into the sky.
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Frequently asked questions
A mushroom cloud is a large cloud of dust that rises into the air in the shape of a mushroom. It is caused by a massive release of heat from a large explosion.
A mushroom cloud is formed when a large volume of lower-density gases is suddenly formed at any altitude. This creates a Rayleigh-Taylor instability, causing a buoyant mass of gas to rise rapidly. The resulting vortex curls 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 "mushroom stem".
A mushroom cloud consists of small particles of radioactive fission products, weapon residues, water droplets, and larger particles of dirt and debris. 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 due to the formation of water droplets.
