This is a picture of the first moments of a nuclear explosion taken in 1952. The blast radius at this moment is less than 20 meters wide.
There are so many extraordinary things about this photo. First off the fact that they had a camera in the 1950's capable of such insanely high speed frame rates (they created a movie from this) that it was capable of 1,000,000 frames per second. In many ways that is more impressive than the nuclear bomb itself.
Second the fact that you can see, in real time, a nuclear explosion as it happens. Those spikes at the bottom are called the "rope trick effect" which is caused by the support cables inside or holding up the bomb. The light radiation is so intense it vaporizes anything nearby causing things to explode just from the intensity of the light itself (before radiation has any effect at all). So those spikes are literally just the support cables exploding in the extraordinarily bright light from the bomb.
