'Mushroom cloud' spotted in Siberia

Residents of the Kemerovo Region were frightened by an unusual, mushroom-shaped cloud, reminiscent of a nuclear explosion. The distinctive cloud appeared in the sky at about 6 p.m. on Sunday, witnesses posted on social media. The phenomenon could be observed for about 40 minutes, until the cloud dissipated.

Some eyewitnesses were alarmed by the scene. "When I saw this cloud, I was stunned; it was scary, to be honest," @ksenia_pkp wrote on Instagram. Some users suggested that the cloud could have formed as a result of a powerful explosion at a nearby coal mine.

But Russian media quickly published a statement from law enforcement agencies refuting rumors about accidents in the region.

"There are no reports of fires or explosions recorded in the area, and the 'mushroom' hanging over the city is a regular rain cloud," Life television reported, citing a law enforcement source.

"What we can see in the photos leads us to agree with the conclusions of the emergency services that this is, indeed, a rather peculiarly shaped cumulus cloud," Pavel Konstantinov, head of the meteorological department of Moscow State University's Meteorological Observatory, told RBTH.

The appearance of such a cloud can be explained by the difference in temperatures at the surface and at a higher altitude, he said. "This happened either because it was abnormally hot in this spot nearer the ground, or it was abnormally cold higher up in the atmosphere," Konstantinov said. "Due to the temperature difference, the air lower down instantly began to rise."

The formation of such a cumulus cloud is fundamentally similar to the process that forms a nuclear mushroom cloud, the expert explained.

"A nuclear explosion is super convection: The surface becomes so hot that the air begins to go up at a very high speed, because it is lighter than cold air," Konstantinov said.

"These are the processes that form clouds like this, with varying degrees of intensity. But if a mushroom cloud is very large, a simple cumulus cloud is much lower and does not look so frightening."

In contrast to a nuclear mushroom, the Kemerovo cloud poses no threat. "This is a rare, interesting phenomenon, but it is absolutely safe," the expert said.

This article originally appeared at Russia Beyond the Headlines.