It is interesting you bring this up. For in my science class, we discussed this recently. Apparently, the explosion was caused by Adam Tessla i think it was, though I am unsure that is his first name. Anyway, Tessla was an American inventor and brilliant man who made a huge electric death ray of sorts that used enourmous capacitors to harness and contain the power taken from lightning. Mind you, this was in 1908. He received no recognition for his inventions and such, while at the same time, Matthew Perry I think it was, made the first trip to the North Pole on a steel ship with all the world watching him. Tessla was jealous and attemped to bounce the electromagnetic energy waves off of the ionosphere and blast the North Pole. As you may or may not know, the ionosphere constantly changes it's altitude. Tessla attempted to calculate the angle at which to bounce the waves but did so incorrectly because he thought the ionosphere was lower than it was. Therefore, his calculations landed the enormous amount of energy directly at Tunguska, Russia. This would accurately explain the phenomena of no crater, no debris, and no other substances found similar to other events of the like, yet, the sky lit up for days because the air was superheated. The effects of the explosion you probably know so i won't get into it.
Now, I'm young and gullible

, but this seems a good explanation as any to decipher this phenomena. Please correct me if I'm wrong.