Recently circulated video footage shows massive clouds rising over several Iranian cities, particularly Tehran, resembling the well known mushroom shape commonly associated with nuclear blasts. This has led some observers to speculate that the scenes may be linked to a nuclear detonation. But does the image alone justify such conclusions?
The mushroom cloud has become embedded in public consciousness as a near certain sign of a nuclear explosion. Physics, however, offers a more precise explanation. The mushroom shape is not a uniquely nuclear signature. Rather, it is a natural outcome of fluid dynamics, specifically what is known as the Rayleigh Taylor instability.
In other words, a mushroom cloud is a general physical phenomenon that can result from various types of explosions or large scale fires, nuclear and non nuclear alike, provided the necessary conditions are present.
The Rise of the Cloud
At the heart of the phenomenon lies thermal buoyancy. When a powerful explosion or an intense fire occurs, it forms a sphere of extremely hot gas with a lower density than the surrounding air.
This density difference generates a buoyant force that propels the hot gas rapidly upward, forming a rising column. As it ascends, the column draws in surrounding air, dust, and water vapour, increasing in size and complexity. This stage resembles the formation of thunderstorm clouds, though on a faster and more violent scale.
As the hot column continues to rise, it reaches more stable atmospheric layers or an altitude at which its density balances with the surrounding air. At that point, it begins to expand horizontally rather than continuing purely vertical ascent.
The central core slows, while the outer edges continue to roll outward. This creates a broad cap atop a relatively narrow stem, producing the characteristic mushroom shape. Shear vortices along the edges of the column play a significant role in shaping and curling the cloud, giving it its distinctive appearance.
Other Types of Explosions
A nuclear explosion releases an immense amount of energy within fractions of a second, producing a fireball with extraordinary temperatures and pressures.
This vast energy generates a powerful and coherent buoyant column that rapidly ascends to great heights, which is why the classic mushroom form appears so prominently in nuclear detonations. Yet the same physical principles apply to other types of explosions. The difference lies mainly in scale and clarity, not in the underlying mechanism.
Large chemical explosions, such as those involving ammunition depots, fuel tanks, or high energy industrial materials, can also generate mushroom shaped clouds if the released energy is sufficiently intense and concentrated over a short period.
This was observed, for example, in the Beirut port explosion several years ago. Although it was a chemical blast rather than a nuclear one, the immense force produced a visible mushroom cloud due to its sheer power.
In such cases, the size of the explosive material, the speed of combustion or decomposition, and the amount of dust or smoke available to be lifted all influence how clearly the mushroom form appears.
Explosive volcanic eruptions can also eject columns of superheated ash and gases high into the atmosphere. If the column is strong enough, it may expand at the top and form a structure resembling a mushroom.
Even without an explosion, massive forest fires can produce strong thermal updrafts that create clouds known as pyrocumulus or pyrocumulonimbus. These clouds may take on a mushroom like appearance when rapidly rising hot air expands at higher altitudes. In such instances, the source is not a shockwave from an explosion but sustained and intense heat release.
Nuclear Indicators
Scientifically speaking, a mushroom cloud cannot be considered conclusive evidence of a nuclear explosion. Reliable distinction depends on other indicators, such as the intensity of the initial flash, shockwave patterns, radiological measurements, and the composition of any subsequent fallout. Visual similarity alone can be misleading if isolated from broader evidence.
As of 1 March 2026, there is no documented and verified evidence of a nuclear detonation inside Iran.
The most relevant reference comes from reports citing the International Atomic Energy Agency on 28 February 2026, which stated that it had not detected any radiological traces associated with the recent strikes. This weakens the hypothesis of a nuclear explosion or any publicly detectable radioactive contamination.
A nuclear detonation typically leaves signatures that are difficult to conceal, including radiological indicators, detection of noble gases such as xenon through monitoring networks in neighbouring countries, or distinctive seismic signals if the explosion occurs underground. To date, there are no indications that such markers have been observed.
